User blog:BEJT/Time Travel, Timelines, the Multiverse, and Related Topics: The Marvel Cinematic Universe's Rules

Introduction
Time travel is an incredibly messy thing, and Avengers: Endgame in particular has led to endless debates about the rules in the MCU. Over recent years, the MCU has set about establishing its rules when it comes to time travel, being different to the classic sci-fi film rules of rewriting a timeline. It makes their story approach much fresher, but also comes with massive complications. It has felt like an uncontrollable mess of linked questions and knock-on implications and can really mess with the head. In the end, I decided I had to compile it all and try to get it under control, while making some sense of the questions. Compiling every quote I could find, and intending to add any more as they come, I have tried to strip every quote to the bone and dissect them very thoroughly. Over time, any questions and links between questions that have come to mind I have tried to compile for the blog. I have then taken all the quotes and dissections and sorted them into the questions they pertain to, structuring the questions to answer certain ones first to then help answer further ones. I have then let the blog take me wherever it heads, trying not to bring any personal biases into it, to end up at the best results.

Any particularly important quotes and dissections I have highlighted in bold. Where there are disparities between U.K. English and U.S. English spellings, I have used the characters' nationality's spelling - for example, for Jemma Simmons I use U.K. English, for most characters U.S. English. When writing myself, not in quotes, I use my native U.K. English.

A few notes: Not much of the blog is in bold. I intend to go through and make more key quotes and dissections bold at some point soon. Different parts of the blog were written at different times, some with more time and effort and others more rushed, and learning and improving as I go so earlier-written parts not being as developed. It was not written in order. I hope to strengthen the blog in its weaker sections and make it more consistent at some point soon. While I have tried to be unbiased, I am not sure I have been quite as charitable to certain interpretations as I should be to be fully impartial in some places where bits were written in more of a hurry. Again, I hope to make it more consistent at some point soon. Some slight structural improvements to the order of questions will come at some point soon. Marvel's Runaways involves things relating to time and the future, but has not established any rules yet, so the show does not factor into this blog at the moment.

Quote

 * 1953 Peggy Carter: "That was a difficult winter. A blizzard had trapped half our battalion behind the German line. Steve - Captain Rogers - he fought his way through a Hydra blockade that had pinned our allies down for months. He saved over a thousand men. Including the man who would uh, who would become my husband, as it turned out. Even after he died, Steve was still changing my life."
 * Change of scene.
 * Steve Rogers: "You should be proud of yourself, Peggy."
 * Steve and Peggy look at photos of Peggy with her children, no husband.
 * 2014 Peggy Carter: "Mmm. I have lived a life. My only regret is that you didn't get to live yours."
 * Steve looks concerned.
 * 2014 Peggy Carter: "What is it?"
 * Steve Rogers: "For as long as I can remember, I just wanted to do what was right. I guess I'm not quite sure what that is anymore. And I thought I could throw myself back in and follow orders. Serve. It's just not the same."
 * 2014 Peggy Carter: "You're always so dramatic. Look, you saved the world. We rather... mucked it up."
 * Steve Rogers: "You didn't. Knowing that you helped found S.H.I.E.L.D. is half the reason I stay."
 * 2014 Peggy Carter: "Hey. The world has changed, and none of us can go back. All we can do is our best. And sometimes the best that we can do is to..."
 * Peggy starts coughing.
 * 2014 Peggy Carter: "... start over."
 * Peggy coughs and then her expression goes blank.
 * 2014 Peggy Carter: "Steve..."
 * Steve Rogers: "Yeah?"
 * 2014 Peggy Carter: "Wh-? Y-You're alive! You, you came, you came back!"
 * Steve Rogers: "Yeah, Peggy."
 * 2014 Peggy Carter: "It's been so long. So long."
 * Steve Rogers: "Well, I couldn't leave my best girl. Not when she owes me a dance."

Dissecting

 * 1953 Peggy Carter: "That was a difficult winter. A blizzard had trapped half our battalion behind the German line. Steve - Captain Rogers - he fought his way through a Hydra blockade that had pinned our allies down for months. He saved over a thousand men. Including the man who would uh, who would become my husband, as it turned out. Even after he died, Steve was still changing my life."
 * Peggy says that her husband is a man who was saved by Steve Rogers. However, this is not evidence against Steve Rogers being her husband, as Peggy would lie in such a manner to cover the fact that Steve is her husband, if indeed that is the case, since time-travelled Steve would be keeping his true identity hidden. Since the same writers, Markus and McFeely, wrote both Captain America: The Winter Soldier and Avengers: Endgame, and it is their intention that this is the case, then it is definitely more than possible.
 * Change of scene.
 * Steve Rogers: "You should be proud of yourself, Peggy."
 * Steve and Peggy look at photos of Peggy with her children, no husband.
 * The photos do not include a husband. There could be in-universe reasons for this: Peggy and her husband divorced some time after the 1953 interview, Peggy's husband passed away some time after the 1953 interview, or he simply was not present for the photos. If he passed away or was not present for the photos, it would still be strange that she chooses not to have a photo of him by her, alongside her children, but still. However, the reason, it would seem, was to leave the options open for who they ended up making her husband. The writers then claim that it was their intention to write Avengers: Endgame in such a way that indeed, Steve is the missing husband. This certainly makes sense here, with Peggy not including photos of her husband on her desk since her husband was kept mostly secret and lying low, to make sure no one works it out, and especially so Steve does not see it.
 * 2014 Peggy Carter: "Mmm. I have lived a life. My only regret is that you didn't get to live yours."
 * Steve looks concerned.
 * 2014 Peggy Carter: "What is it?"
 * Steve Rogers: "For as long as I can remember, I just wanted to do what was right. I guess I'm not quite sure what that is anymore. And I thought I could throw myself back in and follow orders. Serve. It's just not the same."
 * 2014 Peggy Carter: "You're always so dramatic. Look, you saved the world. We rather... mucked it up."
 * Steve Rogers: "You didn't. Knowing that you helped found S.H.I.E.L.D. is half the reason I stay."
 * 2014 Peggy Carter: "Hey. The world has changed, and none of us can go back. All we can do is our best. And sometimes the best that we can do is to..."
 * Peggy starts coughing.
 * 2014 Peggy Carter: "... start over."
 * Peggy coughs and then her expression goes blank.
 * 2014 Peggy Carter: "Steve..."
 * Steve Rogers: "Yeah?"
 * 2014 Peggy Carter: "Wh-? Y-You're alive! You, you came, you came back!"
 * Peggy is presented as having Alzheimer's disease. This would mean that she starts to lose shorter term memories, only remembering more embedded memories, further back. People, tragically, start to forget their spouses and other important memories. It has been suggested by some that Peggy being surprised Steve is alive is a point against the idea that Steve was her husband, but it is more than possible that Peggy in this moment does not remember what happened to Steve beyond her grief after losing him.
 * Steve Rogers: "Yeah, Peggy."
 * 2014 Peggy Carter: "It's been so long. So long."
 * Steve Rogers: "Well, I couldn't leave my best girl. Not when she owes me a dance."
 * It is also even possible, from the, "It's been so long. So long," that Peggy has in fact not entirely forgotten Steve was her husband anyway (if indeed he was). Just that she thinks she hasn't seen Steve, her husband, in a very long time, forgetting recent years of memories, and she's surprised and confused to see him in fact for this reason. Either explanation fits, which makes sense, since the writers of both films wrote at least Avengers: Endgame to fit this way, if not also Captain America: The Winter Soldier, depending on how much they had planned the husband reveal when writing c. 2013.

Quote

 * Daisy Johnson: "I can change it."
 * Leo Fitz: "No."
 * Daisy Johnson: "We can reverse-engineer the visions, figure out where this went down, and get there ahead of it."
 * Jemma Simmons: "Save that poor man."
 * Leo Fitz: "You can't. I mean, fourth-dimensionally speaking, is all. If you saw the future, then... that's the future."
 * Daisy Johnson: "I don't want to believe that. I can't explain how it felt, but it was awful. I felt so helpless. I was inches away from him. I have to save him."
 * Lincoln Campbell: "Edwin called in with your name for a reason. Maybe you're meant to change it."
 * Phil Coulson: "And we know what this homeless man, Charles, looks like."
 * Melinda May: "And we're running a search."
 * Phil Coulson: "If Daisy can remember details about the location and we get there in time, we -"
 * Leo Fitz: "Guys, there is no time. She glimpsed the fourth dimension. Time is an illusion. It's how we perceive the fourth dimension. Simmons..."
 * Jemma Simmons: "It's mathematics. He's talking about space-time."
 * Leo Fitz: "How do you-? How can I explain this? Right..."
 * Fitz picks up a wad of paper.
 * Leo Fitz: "We're 3-D, yeah? Okay, but imagine, imagine we lived in a 2-dimensional existence. Flat, just like a piece of paper. We wouldn't be able to conceive of three dimensions, of, of, of a, a cube or... anything that's not 2-dimensional, okay?"
 * Phil Coulson: "Yeah."
 * Leo Fitz: "Right, so, we flat, paper people..."
 * Fitz draws a line along the side of the wad.
 * Leo Fitz: "... would perceive this 3-dimensional cube as many separate 2-dimensional moments. As..."
 * Fitz flicks through the paper wad like a flip book.
 * Leo Fitz: "... time passing, the point on the line traveling through space and time."
 * Jemma Simmons: "But, in fact, the cube, the line, is fixed."
 * Leo Fitz: "Yeah, it's just sitting there. There's no future. There's no past. It just... it just is. And nothing you can do will change that."

Dissecting

 * Daisy Johnson: "I can change it."
 * Leo Fitz: "No."
 * Daisy Johnson: "We can reverse-engineer the visions, figure out where this went down, and get there ahead of it."
 * Jemma Simmons: "Save that poor man."
 * Leo Fitz: "You can't. I mean, fourth-dimensionally speaking, is all. If you saw the future, then... that's the future."
 * Fitz is explaining that time already all exists, fourth-dimensionally speaking. We just happen to be currently perceiving a certain point in the timeline.
 * Daisy Johnson: "I don't want to believe that. I can't explain how it felt, but it was awful. I felt so helpless. I was inches away from him. I have to save him."
 * Lincoln Campbell: "Edwin called in with your name for a reason. Maybe you're meant to change it."
 * Phil Coulson: "And we know what this homeless man, Charles, looks like."
 * Melinda May: "And we're running a search."
 * Phil Coulson: "If Daisy can remember details about the location and we get there in time, we -"
 * Leo Fitz: "Guys, there is no time. She glimpsed the fourth dimension. Time is an illusion. It's how we perceive the fourth dimension. Simmons..."
 * Jemma Simmons: "It's mathematics. He's talking about space-time."
 * Fitz is talking about space-time and how the fourth dimension just already is.
 * Leo Fitz: "How do you-? How can I explain this? Right..."
 * Fitz picks up a wad of paper.
 * Leo Fitz: "We're 3-D, yeah? Okay, but imagine, imagine we lived in a 2-dimensional existence. Flat, just like a piece of paper. We wouldn't be able to conceive of three dimensions, of, of, of a, a cube or... anything that's not 2-dimensional, okay?"
 * Phil Coulson: "Yeah."
 * Leo Fitz: "Right, so, we flat, paper people..."
 * Fitz draws a line along the side of the wad.
 * Leo Fitz: "... would perceive this 3-dimensional cube as many separate 2-dimensional moments. As..."
 * Fitz flicks through the paper wad like a flip book.
 * Leo Fitz: "... time passing, the point on the line traveling through space and time."
 * Jemma Simmons: "But, in fact, the cube, the line, is fixed."
 * This is a good explanation of the space-time continuum and how time is already fixed, with present just being our perception in a current 3-D moment and either side of our current moment being labelled past and future.
 * Leo Fitz: "Yeah, it's just sitting there. There's no future. There's no past. It just... it just is. And nothing you can do will change that."
 * Time already sits the way it was and always will be that way. If you glimpsed the future, then you have glimpsed the future. This turns out true, everything plays out as foreseen, both in this episode and then in the rest of the season leading up to Lincoln's death in Ascension.

Quote

 * Steve Rogers: "When you were spying on me from across the hall..."
 * Sharon Carter: "You mean when I was doing my job."
 * Steve Rogers: "Did Peggy know?"
 * Sharon Carter: "She kept so many secrets. I didn't want her to have one from you."

Dissecting

 * Steve Rogers: "When you were spying on me from across the hall..."
 * Sharon Carter: "You mean when I was doing my job."
 * Steve Rogers: "Did Peggy know?"
 * Sharon Carter: "She kept so many secrets. I didn't want her to have one from you."
 * Peggy kept lots of secrets in her life. It is very possible that her husband's true identity was one of her secrets, keeping him fairly private and lying to cover who he really was, if indeed he was Steve all along.

Quote

 * Ancient One: "We harness energy drawn from other dimensions of the multiverse."
 * Karl Mordo: "Temporal manipulations can create branches in time. Unstable dimensional openings. Spacious paradoxes! Time loops!!! You want to get stuck reliving the same moment over, and over, forever, or never having existed at all?

Dissecting

 * Ancient One: "We harness energy drawn from other dimensions of the multiverse."
 * The different dimensions are parts of the multiverse.
 * Karl Mordo: "Temporal manipulations can create branches in time."
 * Branches in time, whatever that exactly means, can be created when manipulating time.
 * Karl Mordo: "Unstable dimensional openings. Spacious paradoxes! Time loops!!! You want to get stuck reliving the same moment over, and over, forever, or never having existed at all?
 * The rest of the time-related things in Doctor Strange are done without complication. What he does with the Time Stone is merely turn the apple and book backwards and forwards in their personal existence, and then he does the same to the city in Hong Kong, just on a grander scale. There is no actual turning back of time. Then the time loop is fairly clear, Strange flies off then traps himself and Dormammu in a loop while no time is passing outside of their bubble, then once he's done he returns, immediately after he left. So, the time loop described here is not a problem with time travel and changing timelines and things. The meaning behind what Mordo says about "never having existed at all" is unclear, if this implies some rewriting of a timeline (said elsewhere to be impossible) or just that some other mistake he might make when meddling with something as powerful as an Infinity Stone that controls time could erase himself from existence in some manner.

Quote
[...]
 * Deke Shaw: "When? What year?"
 * Phil Coulson: "That monolith was different, wasn't it? We didn't travel through space."
 * Jemma Simmons: "No reason to send a message back to Earth. We're already here."

Dissecting

 * Deke Shaw: "When? What year?"
 * Phil Coulson: "That monolith was different, wasn't it? We didn't travel through space."
 * The unspoken line here is clearly, "We traveled through time." The first monolith purely functioned on transport through space, the White Monolith purely functions on transport through time. This would imply no different universe-shifting of any sort, purely shifting across time.
 * Jemma Simmons: "No reason to send a message back to Earth. We're already here."
 * Simmons realises they don't need to send a message back to where they have come from, since they're already here. This implies that it's the same place as where they left - they never left, just moved through time. It is not some alternate universe, it's their home, decades on. It is possible that Simmons is simply making an assumption that is incorrect, but this nonetheless appears to be the writers communicating this idea.

Quote
[...] [...] [...] [...]
 * Melinda May: "This is Earth."
 * Phil Coulson: "We're in the future!"
 * Jemma Simmons: "It's all destroyed. Coulson, please, tell me it's impossible."
 * Phil Coulson: "I think we can all agree at this point that anything is possible. Glad you're alright. Your guy, Virgil. He didn't tell you anything else about his plan to bring us back from the past?"
 * Deke Shaw: "I'm just still trying to fit all these ideas inside my skull."
 * Phil Coulson: "And you haven't heard anything about a gateway? A rock that transports people?"
 * Deke Shaw: "If I had, do you think I'd still be here?"
 * Jemma Simmons: "There was no second monolith when I landed on Maveth."
 * Melinda May: "So, we'll have to find our own way back."
 * Jemma Simmons: "Well, I'm a biologist, but sure, I can invent time travel."
 * Deke Shaw: "Remember all that deranged garbage that Virgil was always spouting about people arriving from the past? I think you're looking at 'em."
 * Tess: "That's insane."
 * Melinda May: "Doesn't mean it's not true."
 * Jemma Simmons: "We came through a gateway, some sort of temporal shift."
 * Tess: "Stories from when we were kids. Some of the elders swore that a group called S.H.I.E.L.D. would come from the past to help us."
 * Daisy Johnson: "Does that line work in the future?"
 * Deke Shaw: "I guess not."
 * Melinda May: "Fitz would be going out of his mind."
 * Jemma Simmons: "Time is strange. Somewhere out there, he's still fighting. But from our reference point, he's lived his life. Or not."

Dissecting

 * Melinda May: "This is Earth."
 * Phil Coulson: "We're in the future!"
 * Again, it's Earth (the Earth, not another), and they're in the future. And again, the agents could in-universe just be mistaken, but this nonetheless seems to be the writers communicating the idea.
 * Jemma Simmons: "It's all destroyed. Coulson, please, tell me it's impossible."
 * Phil Coulson: "I think we can all agree at this point that anything is possible. Glad you're alright. Your guy, Virgil. He didn't tell you anything else about his plan to bring us back from the past?"
 * They've been brought forward from the past, not another past. Same point about possible mistakes but the writers' intent.
 * Deke Shaw: "I'm just still trying to fit all these ideas inside my skull."
 * Phil Coulson: "And you haven't heard anything about a gateway? A rock that transports people?"
 * Deke Shaw: "If I had, do you think I'd still be here?"
 * Jemma Simmons: "There was no second monolith when I landed on Maveth."
 * Melinda May: "So, we'll have to find our own way back."
 * Jemma Simmons: "Well, I'm a biologist, but sure, I can invent time travel."
 * To get back, they have to travel through time, not back to their previous universe. Same point about possible mistakes but the writers' intent.
 * Deke Shaw: "Remember all that deranged garbage that Virgil was always spouting about people arriving from the past? I think you're looking at 'em."
 * The past again (if Deke is correct, but this nonetheless communicates the writers' intent).
 * Tess: "That's insane."
 * Melinda May: "Doesn't mean it's not true."
 * Jemma Simmons: "We came through a gateway, some sort of temporal shift."
 * This lays it out clearly as a gateway shifting you through time, and only that (if Simmons is correct, but this nonetheless communicates the writers' intent).
 * Tess: "Stories from when we were kids. Some of the elders swore that a group called S.H.I.E.L.D. would come from the past to help us."
 * The past again (if Tess is correct, but this nonetheless communicates the writers' intent).
 * Daisy Johnson: "Does that line work in the future?"
 * The future again (if Daisy is correct, but this nonetheless communicates the writers' intent).
 * Deke Shaw: "I guess not."
 * Melinda May: "Fitz would be going out of his mind."
 * Jemma Simmons: "Time is strange. Somewhere out there, he's still fighting. But from our reference point, he's lived his life. Or not."
 * Fitz (not another Fitz, she's referring to "Fitz", her Fitz) would have lived his life from the point they are at, suggesting this is just the same timeline, decades later (if Simmons is correct, but this nonetheless communicates the writers' intent).

December 1, 2017: Entertainment Weekly - Whedon and Bell Interview
https://ew.com/tv/2017/12/01/agents-of-shield-time-jump-space-spoilers/

Quote
[...] [...]
 * Natalie Abrams: "How far into the future are they?"
 * Jed Whedon: "We'll say definitively how far they're in the future in a few episodes, but the idea is 70 + years in the future."
 * Jeff Bell: "We're X number of years in the future, and this is what this person knows."
 * Natalie Abrams: "Is the driving force of this season whether they can actually prevent the destruction of Earth?"
 * Jed Whedon: "That would be interesting. Yeah, what we're seeing is a horrible future that no one wants to have exist, so the first problem is trying to repair it, but maybe there's a bigger question of "Does it ever need to happen?""
 * Natalie Abrams: "How will Daisy handle knowing she supposedly caused the cataclysmic event that led to the end of the world?"
 * Jeff Bell: "I would say she's going to question everything about herself because she would say, "I didn't do it.""
 * Jed Whedon: ""I don't believe it because I didn't do it.""
 * Jeff Bell: ""I didn't do it, I would remember it if I had done it," but he'll say, "Yeah, but that's because you came to the future, what if you hadn't? The you that didn't, or whatever, could've done that.""

Dissecting

 * Natalie Abrams: "How far into the future are they?"
 * Jed Whedon: "We'll say definitively how far they're in the future in a few episodes, but the idea is 70 + years in the future."
 * Another comment about the future.
 * Jeff Bell: "We're X number of years in the future, and this is what this person knows."
 * Another comment about the future.
 * Natalie Abrams: "Is the driving force of this season whether they can actually prevent the destruction of Earth?"
 * Jed Whedon: "That would be interesting. Yeah, what we're seeing is a horrible future that no one wants to have exist, so the first problem is trying to repair it, but maybe there's a bigger question of "Does it ever need to happen?""
 * The agents are hopeful that it doesn't ever need to happen. This would suggest that when they are successful in The End, they are successful in that regard, somehow making sure it in some way doesn't happen.
 * Natalie Abrams: "How will Daisy handle knowing she supposedly caused the cataclysmic event that led to the end of the world?"
 * Jeff Bell: "I would say she's going to question everything about herself because she would say, "I didn't do it.""
 * Jed Whedon: ""I don't believe it because I didn't do it.""
 * Jeff Bell: ""I didn't do it, I would remember it if I had done it," but he'll say, "Yeah, but that's because you came to the future, what if you hadn't? The you that didn't, or whatever, could've done that.""
 * This gives some further context to the confusing conversation in the next episode. When Deke starts suggesting that they might be a different part of the multiverse, Bell's comment would suggest he specifically means that they've jumped out of the timeline but continued down the timeline where they're supposed to have stayed and then arrived in the future of a timeline where they never left. This is disproved by the rest of the season and the evidence that the agents always go to the future and then return, but still end up destroying the planet. I go into it more in that next episode's discussion.

Quote

 * Daisy Johnson: "How could I split the world apart? My powers aren't that strong. I am not that strong."
 * Deke Shaw: "Maybe not yet, but you will be."
 * Daisy Johnson: "And how do you know that?"
 * Deke Shaw: "Because planet Earth went from smooth to chunky, and Quake is the one who did it."
 * Daisy Johnson: "And you don't think I'd remember that?"
 * Deke Shaw: "Well, actually, not according to the multiverse theory. You probably never heard of it, but in quantum physics, there's a theory that, for every universe, there are infinite parallel universes. So in my universe, you destroyed the planet. Maybe that just hasn't happened in -"
 * Daisy slaps Deke.
 * Daisy Johnson: "So what universe did that just happen in? Mine or yours?"

Dissecting

 * Daisy Johnson: "How could I split the world apart? My powers aren't that strong. I am not that strong."
 * Deke Shaw: "Maybe not yet, but you will be."
 * Daisy Johnson: "And how do you know that?"
 * Deke Shaw: "Because planet Earth went from smooth to chunky, and Quake is the one who did it."
 * Deke here implies that Daisy will go back in time and grow in power, then split the world apart, because that's the way it has always been, so that's what will happen, it just hasn't for her yet.
 * Daisy Johnson: "And you don't think I'd remember that?"
 * The simple response here, and what the conversation so far has suggested will be the response, is that she will go back and then it will happen.
 * Deke Shaw: "Well, actually, not according to the multiverse theory. You probably never heard of it, but in quantum physics, there's a theory that, for every universe, there are infinite parallel universes. So in my universe, you destroyed the planet. Maybe that just hasn't happened in -"
 * Deke switches gears into talking about the multiverse, which would essentially suggest he is wondering whether this is, in fact, not the Daisy who destroyed his world, but rather another universe's Daisy, which doesn't line up with the earlier part of the conversation. Unless he has essentially been saying, "Well, your power is still at a 7 but you're still only 28. I have evidence to suggest that you're going to grow in power over the coming months to a 10, because I know that Quake, by about age 29, is a power level 10, since the Quake in my universe is a power level 10 by about age 29, and you're at the very least very nearly the same person."
 * Still, this is a strange reply to her saying she doesn't remember. The reason is, "You haven't done it, at least yet," regardless of the multiverse - either she just hasn't done it yet from her perspective because she hasn't gone back to 2017 yet, or she just hasn't done it yet from her perspective because she was plucked from a universe at a time before she is set to do it. I guess the reason the conversation heads in this direction is that they can't know that Daisy will get back. So Daisy is essentially saying, "Well, I've just been taken from 2017 with no prospect of return, and I hadn't destroyed the world yet, so, unless you're saying I just happen to have destroyed the world before I left and I don't remember it...", to which Deke is then saying, "Well, sure, you've been plucked from 2017 with no prospect of return, but that doesn't change the fact that Quake destroyed my world, so, assuming you don't get back to 2017, how can Quake have destroyed the world? Well, maybe the answer is that you're a Quake from another universe, so it doesn't change the fact that in my universe's past, my universe's Quake destroyed the world." In which case, it's odd that he is in fact accusing specifically the Quake he's talking to of destroying the world - unless it's just because he's angry at Quake in general for destroying the world and angry at this one too because she's, for all intents and purposes, the same woman who would, in the same circumstances, end up doing the same thing - but also, it means his point is moot, as Daisy does end up going back in time. So we can likely just chalk this up to the characters not knowing they can get back yet, and the writers just finding a way to introduce the multiverse theory.
 * So, all else aside, it's still worth noting that the writers are introducing the multiverse theory here as a "Chekhov's Multiverse", clearly intentionally planted in the dialogue to in some way be part of the whole conundrum.
 * Daisy slaps Deke.
 * Daisy Johnson: "So what universe did that just happen in? Mine or yours?"
 * Deke seems to have essentially just said, "Technically, you might now have done it to my world," so it's a little odd that she slaps him - but it still makes sense, she's angry at him in general for the accusations levied against any version of her being capable of/culpable for the destruction of Earth.
 * The writers essentially confirm here what was already obvious, that if Deke had finished his sentence, he would have said "in your universe yet".

Quote
[...] [...]
 * Kasius: "Despite all I did for these humans, I found them clinging to their gods, their fairy tales, one of which was Quake. The Old Ones, rest their souls they used to tell the story of how S.H.I.E.L.D. would return one day from the past to save them. Now here you are."
 * Kasius: "Sinara is concerned about the prophecy that others from the past might have come, as well."
 * Kasius: "Did you come through time together or separately?"

Dissecting

 * Kasius: "Despite all I did for these humans, I found them clinging to their gods, their fairy tales, one of which was Quake. The Old Ones, rest their souls they used to tell the story of how S.H.I.E.L.D. would return one day from the past to save them. Now here you are."
 * Another comment about the past.
 * Kasius: "Sinara is concerned about the prophecy that others from the past might have come, as well."
 * Another comment about the past.
 * Kasius: "Did you come through time together or separately?"
 * Kasius says they have come through time, not across to another universe (if Kasius is correct, but this nonetheless communicates the writers' intent).

Quote
[...] [...] [...] [...] [...] [...] [...] [...] [...]
 * Leo Fitz: "Where are they?"
 * Enoch: "2-0-9-1. Earth Year 2-0-9-1."
 * Leo Fitz: "Why? Why did you send them through that thing?"
 * Enoch: "To fulfill a prophecy. This speaks of the future. They were needed there."
 * Lance Hunter: "You don't seriously believe all this, do you? A prophecy and a monolith that sends you through time?"
 * Leo Fitz: "Send me through to them."
 * Enoch: "The stone can only be activated from the other end. I only knew when it would open. I have no knowledge of who opened it."
 * Leo Fitz: "You sent my friends into the future."
 * Leo Fitz: "Her father was an Inhuman. Every time he touched someone, he and that person would have a vision of an impending death. And it must have been torturous. So he couldn't have any human contact. Not with his wife. Not with his, not his baby daughter."
 * Lance Hunter: "And they still call these "gifts"?"
 * Leo Fitz: "He saved Daisy. And she was convinced that she could save him, change the future, but -"
 * Lance Hunter: "What's written is written."
 * Polly Hinton: "Her mind has been scattered. Past, present, future it's all the same to her, all mixed up. Sometimes, she doesn't even know I'm her mother."
 * Leo Fitz: "They're in trouble some 70 years in the future, and there's nothing I can do?"
 * Lance Hunter: "They're stuck 70-odd years in the future, and our world's about to end."
 * Polly Hinton: "How does this get Fitz to the future?"
 * Leo Fitz: "It's a cryo-freeze chamber."
 * Lance Hunter: "What?!"
 * Leo Fitz: "Yeah. I'm taking the long way there. Gonna sleep for 74 years."
 * On-screen: "74 years later".

Dissecting

 * Leo Fitz: "Where are they?"
 * Enoch: "2-0-9-1. Earth Year 2-0-9-1."
 * Enoch is direct here. They're in the year 2091. Not another universe's 2091, just 2091. They have been shifted to another year, that's all.
 * Leo Fitz: "Why? Why did you send them through that thing?"
 * Enoch: "To fulfill a prophecy. This speaks of the future. They were needed there."
 * There has been a prophecy of the future in which the agents arrive from 2017, so the events of Episodes 1-4 should indeed be the future, not an alternate future, for them to be prophesied. A prophecy of the future would otherwise not see the agents come from 2017, since that would not be the future.
 * Lance Hunter: "You don't seriously believe all this, do you? A prophecy and a monolith that sends you through time?"
 * The White Monolith is again said to send you "through time", purely time, the same way the previous monolith sent you purely through space.
 * Leo Fitz: "Send me through to them."
 * Enoch: "The stone can only be activated from the other end. I only knew when it would open. I have no knowledge of who opened it."
 * If the White Monolith opens a gateway through time and someone in 2091 opened a connection to 2017, there is no reason it would randomly connect to another universe's 2017. It would just connect to 2017. This again suggests that the White Monolith purely shifted them through time.
 * Leo Fitz: "You sent my friends into the future."
 * Another comment about the future.
 * Leo Fitz: "Her father was an Inhuman. Every time he touched someone, he and that person would have a vision of an impending death. And it must have been torturous. So he couldn't have any human contact. Not with his wife. Not with his, not his baby daughter."
 * Lance Hunter: "And they still call these "gifts"?"
 * Leo Fitz: "He saved Daisy. And she was convinced that she could save him, change the future, but -"
 * Lance Hunter: "What's written is written."
 * As shown in Spacetime, Charles Hinton's power involved seeing the future. Not another future, the future, that then played out. Robin has adopted a power in the same vein, minus the seeing a death part. With Robin seeing events from the near future through to 2091 throughout the season, and her power clearly being to see the future, that plays out, not a possible future or another universe's future, this would again mean that the 2091 we see play out is the future.
 * Polly Hinton: "Her mind has been scattered. Past, present, future it's all the same to her, all mixed up. Sometimes, she doesn't even know I'm her mother."
 * Again, Robin's mind is scattered across the timeline. She sees the past, the present, the future, it doesn't matter, it's all the same. Present isn't relevant, her mind just goes to different points on the timeline. Her mind numerous times goes to the 2091 the agents are involved in, so that's the same timeline's 2091.
 * Leo Fitz: "They're in trouble some 70 years in the future, and there's nothing I can do?"
 * Another comment about the future.
 * Lance Hunter: "They're stuck 70-odd years in the future, and our world's about to end."
 * Another comment about the future.
 * Polly Hinton: "How does this get Fitz to the future?"
 * Another comment about the future.
 * Leo Fitz: "It's a cryo-freeze chamber."
 * Lance Hunter: "What?!"
 * Leo Fitz: "Yeah. I'm taking the long way there. Gonna sleep for 74 years."
 * Again, it's the future of this timeline. Fitz is about to sleep for 74 years so he can wake up in 2091, where he can join his friends, because they're in 2091. Not another 2091. While it's possible that Fitz is mistaken, because they're in an alternate 2091, it shouldn't be possible for Enoch to be wrong, given his knowledge via Robin.
 * On-screen: "74 years later".
 * This confirms it. Essentially, saying "74 years later" is like hitting super fast fast-forward. The show just fast-forwarded through 74 years of the timeline to get to 2091, where the agents are. He got there simply by living long enough (by being frozen). The agents are in 2091, it's that simple. This isn't "74 years later, in another universe", it isn't "now let's switch to focus on another universe's Fitz", it's just the continuation the episode's narrative, following Fitz through.

Quote
[...] [...] [...] [...]
 * Leo Fitz: "You know, I spent 6 months locked up in an off-the-books military prison not to mention 80 years frozen in space all just hoping to find you and here you are. You know, I realized something. The universe can't stop us. 'Cause we've crossed galaxies. We've travelled through time. We've survived the bottom of the Atlantic just so we could be together. Now, a love like that that's stronger than any curse. And you and I we are unstoppable together."
 * Kasius: "In fact, she also traveled through time with the Destroyer of Worlds."
 * Leo Fitz: "How many travelled in time with the Destroyer?"
 * Kasius: "You see, Ben was present when I asked the Destroyer if others had traveled through time with her."
 * Phil Coulson: "We came from the past to save the world."

Dissecting

 * Leo Fitz: "You know, I spent 6 months locked up in an off-the-books military prison not to mention 80 years frozen in space all just hoping to find you and here you are."
 * This is again presented as the Fitz we've been following, not some sudden alternate universe Fitz. And again, yes, if it were a mostly identical parallel universe, he would say the same thing, but it's nonetheless presented by the writers as the Fitz and nothing else.
 * Leo Fitz: "You know, I realized something. The universe can't stop us. 'Cause we've crossed galaxies. We've travelled through time. We've survived the bottom of the Atlantic just so we could be together. Now, a love like that that's stronger than any curse. And you and I we are unstoppable together."
 * The whole sentiment of this quote is that no matter what the universe does to pull them apart, Fitz and Simmons will find their way back to each other. Not that Fitz has been through all of this to reunite with the next best thing, another universe (the main universe)'s Simmons. To propose to and marry what is accidentally another universe's Simmons and not his Simmons. They make their way back to each other no matter what, our Fitz and our Simmons. So, this is all the one universe, the one timeline.
 * Kasius: "In fact, she also traveled through time with the Destroyer of Worlds."
 * Another comment about travelling through time, just time, nothing else (not universes).
 * Leo Fitz: "How many travelled in time with the Destroyer?"
 * Another comment about travelling through time, just time, nothing else (not universes).
 * Kasius: "You see, Ben was present when I asked the Destroyer if others had traveled through time with her."
 * Another comment about travelling through time, just time, nothing else (not universes).
 * Phil Coulson: "We came from the past to save the world."
 * Another comment about the past.

Quote
[...]
 * Alphonso Mackenzie: "Turbo! Man, it's good to see you! How the hell you get in the future?"
 * Leo Fitz: "Uh, the long way."
 * Jemma Simmons: "He needs medical attention. Story time can wait."
 * Alphonso Mackenzie: "Well, not when those stories include time travel."
 * Leo Fitz: "Okay, if you guys really are gonna go fight a bunch of alien warriors, then you might be interested to know that, in the past, I hid a crate of S.H.I.E.L.D. tech in a wall on the base."
 * Alphonso Mackenzie: "Oh, that's what I'm talking about. Thanks, Turbo."
 * Elena Rodriguez: "Where?"
 * Leo Fitz: "Level 3."
 * Alphonso Mackenzie: "Oh..."
 * Elena Rodriguez: "Level..."
 * Alphonso Mackenzie: "... you gotta..."
 * Elena Rodriguez: "... 3?"
 * Alphonso Mackenzie: "... be kidding me."
 * Elena Rodriguez: "You mean the level infested with aliens that suck your blood?"
 * Leo Fitz: "Well, how was I supp- I feel like I'm not getting enough credit here. I have travelled through time and space to find you."

Dissecting

 * Alphonso Mackenzie: "Turbo! Man, it's good to see you! How the hell you get in the future?"
 * Another comment about the future.
 * Leo Fitz: "Uh, the long way."
 * Fitz came the long way to rejoin them. Not rejoin another universe (the main universe)'s version of his friends. They just had different means of travel to get from the same point A to the same point B, not ending up with different universes' versions of each other.
 * Jemma Simmons: "He needs medical attention. Story time can wait."
 * Alphonso Mackenzie: "Well, not when those stories include time travel."
 * Mack assumes Fitz time-travelled the way they did. Another comment about travelling through time, just time, nothing else (not universes).
 * Leo Fitz: "Okay, if you guys really are gonna go fight a bunch of alien warriors, then you might be interested to know that, in the past, I hid a crate of S.H.I.E.L.D. tech in a wall on the base."
 * Again, this is very much presented as just the Fitz we've been following, who we've always followed, through Rewind, putting the tech in the wall, to now. And yes, again, if this were some identical parallel universe he would say the same thing, but there's no reason to assume that when the writers are simply presenting it as just... Fitz.
 * Alphonso Mackenzie: "Oh, that's what I'm talking about. Thanks, Turbo."
 * Elena Rodriguez: "Where?"
 * Leo Fitz: "Level 3."
 * Alphonso Mackenzie: "Oh..."
 * Elena Rodriguez: "Level..."
 * Alphonso Mackenzie: "... you gotta..."
 * Elena Rodriguez: "... 3?"
 * Alphonso Mackenzie: "... be kidding me."
 * Elena Rodriguez: "You mean the level infested with aliens that suck your blood?"
 * Leo Fitz: "Well, how was I supp- I feel like I'm not getting enough credit here. I have travelled through time and space to find you."
 * Again, Fitz has travelled through time and space to find "you", his friends, not a version of his friends from another universe (the main universe).

Quote
[...] [...] [...] [...] [...] [...] [...] [...] [...]
 * Samuel Voss: "It's like her life is a deck of cards shuffled out of order. She's a seer, alright, but nowadays, she can't separate past, present, and future."
 * Phil Coulson: "She's the connection between the two points in time. This is our answer."
 * Melinda May: "The problem is, for her, those two times are indistinguishable."
 * Melinda May: "I asked her why we were taken from the diner."
 * Phil Coulson: "And?"
 * Melinda May: "She said it was the last time we were all seen together."
 * Daisy Johnson: "So, the lady who sees the future says that there isn't one. Super."
 * Daisy Johnson: "The one who sees through time? Probably should've mentioned that."
 * Leo Fitz: "Oh, not the girl's bloody time machine again. It's impossible. You cannot change time. It's fixed."
 * Melinda May: "What if it's not? She's been right about everything else, and for us to even have a chance, you and Simmons have to design the machine."
 * Phil Coulson: "Last time I saw this it sent us to the future. How'd you get a piece of the monolith?"
 * Leo Fitz: "The shard fits into the machine right here."
 * Jemma Simmons: "Maybe that's how it was able to target the monolith across time. This could be our way home."
 * Leo Fitz: "Yeah, but the shard alone isn't enough, we need the whole monolith."
 * Phil Coulson: "It'd be great if Robin could help us fill in the blanks here. Daisy, you knew her first. Maybe you can get through to her."
 * Daisy Johnson: "I can try."
 * Melinda May: "If she helps us get home, maybe none of this ever happens."
 * Jemma Simmons: "This bit here, laser vibrometer. So, it, it measures the resonant frequencies of the monolith piece"
 * Leo Fitz: "And locks onto the frequencies in the monolith through space-time."
 * Leo Fitz: "Nothing we do matters. Because we can't change time."
 * Melinda May: "You don't know that!"
 * Leo Fitz: "Of course I do! Because we've tried! For all I know, we've tried a thousand times! Always ends the same! It's like a record that keeps on skipping, and we are repeating this loop again and again and again!"
 * Melinda May: "Fitz, take a breath!"
 * Leo Fitz: "And every time, Jemma dies. They all die. Robin can't change it. Voss couldn't change it. Even Daisy couldn't change it. She saw the aftermath, and she still destroyed the world."
 * Robin Hinton: "Daisy! Daisy! He has a knife."

Quote

 * Samuel Voss: "It's like her life is a deck of cards shuffled out of order. She's a seer, alright, but nowadays, she can't separate past, present, and future."
 * Again, Robin's powers mean her mind simply jumps around the timeline (like the film Arrival) to different points in her life, out of order. So, when we see Robin in 2017/2018 and she connects to/remembers moments from 2091, that must mean that the 2091 of the main universe is indeed dystopian. Even if, for some reason, the 2091 shown in the first half of the season were that of an alternate universe, that doesn't change the fact that the main universe's future is dystopian, and for it not to be they had to actually, in some capacity, change things - as will be got to later. The reason why some might argue for it being an alternate universe is for it to be that the main universe's timeline just has a nicer future, to link with the idea of not being able to change time - that they just prevented things from going down the same route in their universe. But clearly the future of their universe is dystopian (until they split the timeline) anyway, so the 2091 events from the first half of Season 5 might as well be, considering all the other evidence, the same universe's future and not another one's.
 * Phil Coulson: "She's the connection between the two points in time. This is our answer."
 * Melinda May: "The problem is, for her, those two times are indistinguishable."
 * Again, Robin is a connection between point A and point B in time, not point A in one universe and point B in another. When they return to 2017/2018, Robin is still flitting between the events of 2017/2018 and 2091. They are not distinct for her, they are mixed up, the timeline being mixed up in her head - the one timeline, not mixing up two universes in her head.
 * Melinda May: "I asked her why we were taken from the diner."
 * Phil Coulson: "And?"
 * Melinda May: "She said it was the last time we were all seen together."
 * This further affirms that the specifics of Deke's suggestion to Daisy were based incorrectly on assumptions about not returning to 2017 and just more about introducing the multiverse idea, since Jeff Bell said that what Deke means is perhaps they have been taken to the universe where they never left, but this shows that they were indeed taken from the diner (they're not seen together after since they're underground in the Lighthouse, in hiding).
 * As well as this, May is asking about her and her friends and Robin is recounting the history of this world to answer her question. In other words, these agents were last seen in 2017 of this world, not that another version of these agents were last seen in 2017 and/or that these agents were last seen in 2017 of another world.
 * Daisy Johnson: "So, the lady who sees the future says that there isn't one. Super."
 * Robin sees the future, not another universe's future. So the dystopian 2091 she keeps seeing is the future.
 * Daisy Johnson: "The one who sees through time? Probably should've mentioned that."
 * Robin sees through time, not different universes. So the dystopian 2091 is just another point in time.
 * Leo Fitz: "Oh, not the girl's bloody time machine again. It's impossible. You cannot change time. It's fixed."
 * Fitz reaffirms his stance on time being fixed and unchangeable.
 * Melinda May: "What if it's not? She's been right about everything else, and for us to even have a chance, you and Simmons have to design the machine."
 * The agents are eventually successful, which makes this comment relevant. It is unlikely that the agents were successful but in a completely different way, with the agents being successful, the writers clearly intend for this to be relevant, that May was right: Robin has been right about everything else, with her help, they managed to "change time", finding that time is not "fixed". So their success is through some sort of method of changing time, not just their universe being separate and having a different future.
 * "Change time" also suggest they are in some way making the dystopian timeline less valid after they carve the better future.
 * Phil Coulson: "Last time I saw this it sent us to the future. How'd you get a piece of the monolith?"
 * Another comment about the future.
 * Leo Fitz: "The shard fits into the machine right here."
 * Jemma Simmons: "Maybe that's how it was able to target the monolith across time. This could be our way home."
 * The White Monolith machine, when activated by the True Believers in 2091, targeted the same White Monolith "across time" (in 2017). That's all the White Monolith does, it just connects two points in time, the same way the other monolith connects two points in space. There is no way it could transport you into another universe. The 2091 is the 2091 of the same universe, the same timeline.
 * Leo Fitz: "Yeah, but the shard alone isn't enough, we need the whole monolith."
 * Phil Coulson: "It'd be great if Robin could help us fill in the blanks here. Daisy, you knew her first. Maybe you can get through to her."
 * Daisy Johnson: "I can try."
 * Melinda May: "If she helps us get home, maybe none of this ever happens."
 * May is hopeful that they can prevent this, though this works either way: changing time in some fashion, or making sure it doesn't happen in their universe, if it's a different universe.
 * "None of this ever happens" implies, again, some sort of lessening the validity of this future, even though they are not rewriting the timeline.
 * Jemma Simmons: "This bit here, laser vibrometer. So, it, it measures the resonant frequencies of the monolith piece"
 * Leo Fitz: "And locks onto the frequencies in the monolith through space-time."
 * Again, the White Monolith locks onto another point in the space-time continuum. The universe's space-time continuum. There is no reason it should be able to lock to another point in another universe's space-time continuum.
 * Leo Fitz: "Nothing we do matters. Because we can't change time."
 * Fitz reaffirms his stance again.
 * Melinda May: "You don't know that!"
 * Leo Fitz: "Of course I do! Because we've tried! For all I know, we've tried a thousand times!"
 * This is a slightly odd phrasing, as Fitz is talking about how time cannot be changed and goes on to talk about a loop, implying he is talking about a time loop. Indeed, this chronologically is after his experiences in 2091 (or, if you believe this is an alternate universe, it is after identical events to Fitz's experiences in 2091), including the quotes from the next episode where Fitz comes to decide they are in a time loop, so that is his stance. Yet in a time loop, you technically cannot really count the number of times they have tried, as it's only one, just from a certain perspective it's coming back around an infinite number of times. This quote on its own would somewhat support the theory of a chain of parallel universes rather than a time loop, with him in fact referring to a chain of universes and how there could be a thousand where they've failed so far, who knows exactly? However, in context, it's likely he's simply just using a big number to express the infinite looping nature of a time loop and how from one way of looking at it, they could be on loop 1000, even though that doesn't quite make sense.
 * Leo Fitz: "Always ends the same! It's like a record that keeps on skipping, and we are repeating this loop again and again and again!"
 * Fitz refers to a loop here, which is why it seems like he didn't exactly mean one thousand. The frustration of a loop being that if you are to draw a line and enter into the loop section, you'll just go around and around without ever breaking out, and from that way of looking at it, you could in fact label the number of loops. However, really, they're all just the same one attempt that the line is drawing over again and again.
 * Melinda May: "Fitz, take a breath!"
 * Leo Fitz: "And every time, Jemma dies. They all die. Robin can't change it. Voss couldn't change it. Even Daisy couldn't change it. She saw the aftermath, and she still destroyed the world."
 * Fitz is referring to the 2091 events of the same episode. These 2018-2022 scenes are essentially presented, therefore, as flash-forwards from the agents' perspective (while flashbacks from the timeline's perspective). Fitz is written to be referring to the fact that Voss has shown Daisy what happens (in the 2091 events of this episode), yet she still then went back and, he believes, did it. The implication, it needn't really be said, is that when he's referring to the 2091 events of this episode, he's referring to the 2091 events of this episode, not identical events in another universe. And yes, again, he would say that same thing if it were in fact identical events in another universe, but that's not what the writers at all present.
 * Robin Hinton: "Daisy! Daisy! He has a knife."
 * Robin's mind has gone to 2091, to the events happening in the same episode. Regardless of the interpretation, this scene is in the same universe as the events in 2091 of the same episode. However, this again demonstrates that Robin's powers connect across time and not across universes, which is relevant to other points where her powers are used - unless you are to assume that Robin is seeing the 2091 events of some further parallel universe that played out identically, but again, this is not the way the writers, or indeed the editing, present it.

Quote
[...] [...]
 * Phil Coulson: "For Robin's sake, we need to make sure this world never comes to be."
 * Samuel Voss: "Me and Owen were lockstep in almost everything. Always agreed to pull these people out of the past, but once they got here, we never saw eye-to-eye on that [...] She goes back in time, you already know what will happen."
 * Leo Fitz: "Gravitonium would explain why it's held together."'
 * Jemma Simmons: "And maybe why it was cracked apart."
 * Leo Fitz: "But it being here also means that... It's true. Robin, May it's all true. This is the same design from the Lighthouse, so unless someone else just... happened to come up with the exact same idea... we did this, in the past, after we've lived this moment."
 * Jemma Simmons: "Yeah, the causal loop paradox. We'd only know how to design it because we'd already seen it."
 * Leo Fitz: "Well, we're done for. This is proof."
 * Jemma Simmons: "Uh, I don't know if that's true."
 * Leo Fitz: "Yes, it is. Think about it. There is nothing that we do that matters. This is a bloody time loop. We're doomed to fail."
 * Jemma Simmons: "If we did this, do you know what I see? Proof we make it back."

Dissecting

 * Phil Coulson: "For Robin's sake, we need to make sure this world never comes to be."
 * Again, they are hopeful they can prevent this, but this could fit either way with changing time in some fashion or making sure their universe, if this is a different universe, does not end up the same way.
 * Again, "make sure this world never comes to be" implies that when they are successful in The End, they are in some way making the dystopian timeline less valid.
 * Samuel Voss: "Me and Owen were lockstep in almost everything. Always agreed to pull these people out of the past, but once they got here, we never saw eye-to-eye on that."
 * Another comment about the past.
 * Samuel Voss: "She goes back in time, you already know what will happen."
 * Another comment about travelling through time, just time, nothing else (not universes).
 * Leo Fitz: "Gravitonium would explain why it's held together."
 * Jemma Simmons: "And maybe why it was cracked apart."
 * Leo Fitz: "But it being here also means that... It's true. Robin, May it's all true. This is the same design from the Lighthouse, so unless someone else just... happened to come up with the exact same idea... we did this, in the past, after we've lived this moment."
 * Jemma Simmons: "Yeah, the causal loop paradox. We'd only know how to design it because we'd already seen it."
 * Fitz and Simmons have realised that they've just been given the idea and method of installing gravitonium into Zephyr One, which will then allow them to do it in the past, leading to it being here now to give them to idea, leading to allowing them to do it in the past, etc.. So, they are in a time loop. That's what Fitz is worried about, he's just seen proof they're stuck in a loop.
 * This further suggests a time loop over a chain of universes, not least because Simmons explicitly says "causal loop paradox". The chain of universes interpretation is that the Universe B agents travel from 2017B to Universe A's dystopian 2091, 2091A, before coming back to Universe B's 2017, 2017B, the Earth is destroyed in 2018B, then 2091B is dystopian in the exact same way. Universe C's agents travel from 2017C to 2091B, before coming back to 2017C, the Earth is destroyed in 2019C, then 2091C is dystopian in the exact same way. Universe D's agents travel from 2017D to 2091C, and so on. However, as Fitz is establishing, they get the idea and understanding over the gravitonium from seeing it in 2091, leading them to do it when they get back to 2018, leading to it being there in 2091. But the chain of universes interpretation would mean that the gravitonium has to be installed in the exact same way in Universe A for them to see it in 2091A and get the idea, to then be able to do it in 2018B. But Universe A's agents would never have travelled to another, dystopian universe's 2091, so would never have got the idea or method to install it in that timeline, so it can't be fitted in 2091A for them to learn for Universe B, etc.. This just doesn't fit with a chain, as it requires an initial different universe.
 * This touches on a wider point: The problem of an initial universe. This interpretation requires numerous identical universes, including Universe A, for the agents of Universe B to experience the same 2091 events when they visit 2091A. Except Universe A's agents would have never travelled to a dystopian 2091, so events are, by default, different, let alone the fact that so many events surrounding the destruction of Earth and dystopian future revolve around the fact that the agents got to see the dystopian future. Universe A would have no way of playing out the same way to kick off a chain.
 * Leo Fitz: "Well, we're done for. This is proof."
 * Jemma Simmons: "Uh, I don't know if that's true."
 * Leo Fitz: "Yes, it is. Think about it. There is nothing that we do that matters. This is a bloody time loop. We're doomed to fail."
 * Fitz discusses the time loop they're stuck in, and that due to that, they're bound by predestination.
 * Jemma Simmons: "If we did this, do you know what I see? Proof we make it back."
 * Simmons looks at it the more optimistic way, but it's the same concept. They have to now make it back because in 2017 in the timeline, they made it back. That's just the way it is.

Quote
[...] [...] [...] [...] [...] [...]
 * Deke Shaw: "So, one more time, the machine uses the little piece to trigger the bigger piece through space?"
 * Leo Fitz: "Yeah, or time."
 * Jemma Simmons: "It mirrors the harmonic resonant frequency of photons, which can exist out of space-time."
 * Kasius: "She who predicted they'd come through time. [...] You've never seen the Earth as it was. My father who had better vision than his race who shunned him, called it a hidden blue gem. He and his entire confederacy wanted it for their own. Gather my Inhumans, a fighting force to crush S.H.I.E.L.D.. With them out of the past, my father will then encounter no resistance. Earth waiting for his embrace."
 * Flint: "Yeah, well, still don't know how I'm supposed to build a time machine."
 * Leo Fitz: "It's a portal, not a time machine."
 * 2017 Elena Rodriguez: "Hello? I'm here to help. What's your name?"
 * 2091 Elena Rodriguez: "Elena. It's good to see you."
 * 2017 Elena Rodriguez: "This is a trick."
 * 2091 Elena Rodriguez: "I thought the same thing when I was standing where you are."
 * 2017 Elena Rodriguez: "This isn't real."
 * 2091 Elena Rodriguez: "I wish it were true. An LMD or a Framework illusion - but it's me. I'm you."
 * 2017 Elena Rodriguez: "How? I-"
 * 2091 Elena Rodriguez: "I waited so long to see myself again, still with hope in my eyes."
 * 2017 Elena Rodriguez: "How are you alive?"
 * 2091 Elena Rodriguez: "They killed me, brought me back to take my blood, my DNA, then again and again for years. They revive me when they want, kill me when they don't."
 * 2017 Elena Rodriguez: "What? H-How? How many times?"
 * 2091 Elena Rodriguez: "I held on to the thought of this moment."
 * 2017 Elena Rodriguez: "No. This is wrong."
 * 2091 Elena Rodriguez: "But this time, when they asked me how our team fought back, I tried to give them as little as I could. But I knew you were close. You and Mack. Mack! He's still alive. Hold him for as long as you can."
 * 2017 Elena Rodriguez: "What happens to Mack? What happens?"
 * 2091 Elena Rodriguez: "I practiced so many times what to say. I wanted to be better, save you from the pain. But seeing you - all the pain comes back."
 * 2017 Elena Rodriguez: "You've been here this whole time?"
 * 2091 Elena Rodriguez: "Stuck in the loop. Like you."
 * 2017 Elena Rodriguez: "The loop?"
 * 2091 Elena Rodriguez: "We make it back in time. But then we bring everything that's to come."
 * 2017 Elena Rodriguez: "I, I don't believe that."
 * 2091 Elena Rodriguez: "I know. I don't think I did, either. Until I was on fire, reaching for Mack. And then there was nothing there."
 * 2017 Elena Rodriguez: "Well, you can tell me how to stop it, right? How do we change it?"
 * 2091 Elena Rodriguez: "I'm not sure you can."
 * Deke Shaw: "But none of the time-travelers can go, because you all need to be at the rendezvous when it's turned on, so do the math."
 * 2017 Elena Rodriguez: "Whatever's coming, I'm not afraid to hear it. Tell me how to fight."
 * 2091 Elena Rodriguez: "I want to. I want to help you fix the mistakes. I want to tell you something different than last time. But the more I talk, the more I hear my words echo all over again."
 * 2017 Elena Rodriguez: "It's okay. Take it slow. Just tell me what you remember."
 * 2091 Elena Rodriguez: "I remember feeling helpless. Not being able to change people's choices. His choices."
 * 2017 Elena Rodriguez: "Mack?"
 * 2091 Elena Rodriguez: "No. Coulson."
 * Daisy Johnson: "If I go through that portal, you know it's the beginning of the end."
 * Phil Coulson: "I don't."
 * Change of scene.
 * 2091 Elena Rodriguez: "We made it back home, and we fought to save the world from a future we knew was coming."
 * 2017 Elena Rodriguez: "We have to fight."
 * 2091 Elena Rodriguez: "Of course. But the more we fought, the closer it came."
 * Phil Coulson: "We don't even know you did this."
 * Daisy Johnson: "I was right in the epicenter."
 * Phil Coulson: "I won't let you sacrifice yourself because you're scared of what's to come."
 * Daisy Johnson: "What's to come is the end of everything."
 * Melinda May: "If you can change the future here, you can change it from back home."
 * Daisy Johnson: "But we know this solution works. We can stop this today."
 * Phil Coulson: "No, it's not about today. It's about tomorrow. Even if we solve this problem, the world is never safe. The job goes on. We go on."
 * Change of scene.
 * 2091 Elena Rodriguez: "The team makes one choice, and it ruins everything."
 * 2017 Elena Rodriguez: "A choice to do what?"
 * 2091 Elena Rodriguez: "To save him."
 * 2017 Elena Rodriguez: "What do you mean?"
 * Change of scene.
 * Phil Coulson: "Please."
 * Daisy Johnson: "Maybe I don't go with you. You know it's the right move. Coulson, as an agent of S.H.I.E.L.D., you trained me to fight. Now I'm making my stand, here."
 * Phil Coulson: "May trained you to fight... I need you to lead."
 * 2091 Elena Rodriguez: "Phil Coulson is dying. And you have to let him."
 * 2017 Elena Rodriguez: "Coulson... How? How does he die?"
 * 2091 Elena Rodriguez: "It's already begun. He's sick, and he knows it. We tried to stop it. Loyalty, it cost us the world."
 * 2017 Elena Rodriguez: "You heard all this, and still you couldn't change anything?"
 * 2091 Elena Rodriguez: "I know. Stuck in the loop. But you can forge a different fu- Even as I say the words, I realize I've heard them before."
 * 2017 Elena Rodriguez: "Are you telling me to go back and change the world, or are you warning me that I can't?"
 * 2091 Elena Rodriguez: "You need to go. They're coming."
 * 2017 Elena Rodriguez: "No, not yet."
 * 2091 Elena Rodriguez: "I hope you travel a path to a world I've never seen. Now go."

Dissecting

 * Deke Shaw: "So, one more time, the machine uses the little piece to trigger the bigger piece through space?"
 * Leo Fitz: "Yeah, or time."
 * Jemma Simmons: "It mirrors the harmonic resonant frequency of photons, which can exist out of space-time."
 * Another comment about triggering the piece in 2017 and linking across the space-time continuum, not a different universe or a different space-time continuum.
 * Kasius: "She who predicted they'd come through time."
 * Another comment about travelling through time, just time, nothing else (not universes).
 * Kasius: "You've never seen the Earth as it was. My father who had better vision than his race who shunned him, called it a hidden blue gem. He and his entire confederacy wanted it for their own. Gather my Inhumans, a fighting force to crush S.H.I.E.L.D.. With them out of the past, my father will then encounter no resistance. Earth waiting for his embrace."
 * Another comment about the past.
 * Kasius wants to prevent them from returning to 2017 so he can change time himself, in a different way to what the agents want. If they never get back, his father can win back in the 2010s, and time will be changed in whatever fashion. This does not work if the agents are simply returning to their parallel universe as he would have no way of knowing what his father in that universe is doing in 2017, or if he even exists. It only works through specifically wanting them to not return to the past he is familiar with, meaning they are returning to the past of this universe. And yes, again, Kasius could in-universe be mistaken, but this is what the writers are presenting.
 * Flint: "Yeah, well, still don't know how I'm supposed to build a time machine."
 * Leo Fitz: "It's a portal, not a time machine."
 * I assume the reason Fitz makes this distinction is that it's essentially a portal, a gateway between two points, just two points in time, rather than two points in space. They are not actually travelling in/with the machine like a traditional "time machine".
 * 2017 Elena Rodriguez: "Hello? I'm here to help. What's your name?"
 * 2091 Elena Rodriguez: "Elena. It's good to see you."
 * 2017 Elena Rodriguez: "This is a trick."
 * 2091 Elena Rodriguez: "I thought the same thing when I was standing where you are."
 * 2091 Elena once stood where 2017 Elena is now, she had a conversation with her 2091 self when she was her 2017 self, suggesting a time loop again, that she literally was this 2017 self, though this does not go against the idea of an identical parallel universe she travelled to when she was younger, and there met that universe's 2091 Yo-Yo.
 * 2017 Elena Rodriguez: "This isn't real."
 * 2091 Elena Rodriguez: "I wish it were true. An LMD or a Framework illusion - but it's me. I'm you."
 * 2017 Elena Rodriguez: "How? I-"
 * 2091 Elena Rodriguez: "I waited so long to see myself again, still with hope in my eyes."
 * She knew she was going to see her younger self, which again tells us the agents are in a time loop. If 2091 Elena has lived out her life in her own universe, the one they're in now, distinct from the main universe, then she would have no way of knowing that another universe's 2017 Yo-Yo would join her in the future, because she simply wouldn't know the exact way the future would play out. The only way that would work would be if they still thought it was a time loop and were just mistaken, but things still played out the same anyway. It is much more likely that this is simply a time loop, with Yo-Yo knowing she will see her younger self again.
 * 2017 Elena Rodriguez: "How are you alive?"
 * 2091 Elena Rodriguez: "They killed me, brought me back to take my blood, my DNA, then again and again for years. They revive me when they want, kill me when they don't."
 * 2017 Elena Rodriguez: "What? H-How? How many times?"
 * 2091 Elena Rodriguez: "I held on to the thought of this moment."
 * 2017 Elena Rodriguez: "No. This is wrong."
 * 2091 Elena Rodriguez: "But this time, when they asked me how our team fought back, I tried to give them as little as I could. But I knew you were close. You and Mack. Mack! He's still alive. Hold him for as long as you can."
 * 2091 Elena knows that her 2017 self has limited time left with Mack, that he will die soon. This again should only work if they are in a time loop, as, if the 2017 Elena she's speaking to were to return to her own, distinct universe (the main universe), then there's no reason Mack has to necessarily go on and die. Again, one would have to assume that Yo-Yo is simply mistaken, thinking it's a time loop and also happening to act the exact same way and speak the exact same way to the point where nothing tells her otherwise. The writers are just presenting a time loop.
 * 2017 Elena Rodriguez: "What happens to Mack? What happens?"
 * Not "happened", "happens". 2017 Elena knows this to be in her future, since it happened in 2091 Elena's past, so it should be the same Elena, so all the same one universe and timeline. Yes, again, possible they're making a mistake, but the writers are presenting it as this.
 * 2091 Elena Rodriguez: "I practiced so many times what to say. I wanted to be better, save you from the pain. But seeing you - all the pain comes back."
 * 2017 Elena Rodriguez: "You've been here this whole time?"
 * 2091 Elena Rodriguez: "Stuck in the loop. Like you."
 * 2017 Elena Rodriguez: "The loop?"
 * 2091 Elena Rodriguez: "We make it back in time. But then we bring everything that's to come."
 * Again presented that they're in a time loop. They go back in time and then bring about this future. 2091 Elena says "we", she's referring to them as a collective because she is one of them, not a different universe's version, and "make it"/"then we bring everything" because she's recounting 2017 her's future as she recounts her past, telling 2017 Elena what will happen to her because it's what happened to her. It's a time loop.
 * 2017 Elena Rodriguez: "I, I don't believe that."
 * 2091 Elena Rodriguez: "I know. I don't think I did, either. Until I was on fire, reaching for Mack. And then there was nothing there."
 * 2017 Elena Rodriguez: "Well, you can tell me how to stop it, right? How do we change it?"
 * 2091 Elena Rodriguez: "I'm not sure you can."
 * A time loop that they're not sure it's possible to break out of, like Fitz believes.
 * Deke Shaw: "But none of the time-travelers can go, because you all need to be at the rendezvous when it's turned on, so do the math."
 * Another comment about travelling through time, just time, nothing else (not universes).
 * 2017 Elena Rodriguez: "Whatever's coming, I'm not afraid to hear it. Tell me how to fight."
 * Again, it's coming for 2017 Elena because it's been for 2091 Elena, the future version of herself, not an older version of an alternate her.
 * 2091 Elena Rodriguez: "I want to. I want to help you fix the mistakes. I want to tell you something different than last time. But the more I talk, the more I hear my words echo all over again."
 * This is an indicator of the time loop. No matter what she says, whatever she tries, she finds herself saying the exact same thing she heard when she was her younger self, because it is the exact same thing. If this were a different universe to the one her younger self visited, then she would not be bound to say the same thing she heard, as she's not the same person. She would be able to change even one word, and that would be enough of an indicator that they're not stuck in a time loop. While identical versions of the same character in the same situations might say the same thing, Elena is trying with every word to say something different to what she heard, and wouldn't be unable to. While you might then think that, well, the previous version was also trying to say something different, so she's in the same situation so would try the same thing, this Elena would simply be trying to say something different to the last one, the only one she's aware of, just with the script in her head and all she has to do is say one word differently. She can't, no matter what she does, because it is the exact same conversation, in a time loop.
 * 2017 Elena Rodriguez: "It's okay. Take it slow. Just tell me what you remember."
 * 2091 Elena Rodriguez: "I remember feeling helpless. Not being able to change people's choices. His choices."
 * 2017 Elena Rodriguez: "Mack?"
 * 2091 Elena Rodriguez: "No. Coulson."
 * We go on to then see the frustration Elena goes through as she is unable to change people's choices, like Coulson pushing Daisy to the forefront and trusting her too much. The implication is then that that leads to this Elena, they are the same Elena. Again, yes, possible they're just mistaken, but the writers are presenting it as such.
 * Daisy Johnson: "If I go through that portal, you know it's the beginning of the end."
 * Phil Coulson: "I don't."
 * Change of scene.
 * 2091 Elena Rodriguez: "We made it back home, and we fought to save the world from a future we knew was coming."
 * 2017 Elena Rodriguez: "We have to fight."
 * 2091 Elena Rodriguez: "Of course. But the more we fought, the closer it came."
 * Again, presented as a time loop. No matter what they did, the future was inescapable because it's predestined to be the way they've seen it to be.
 * Phil Coulson: "We don't even know you did this."
 * Daisy Johnson: "I was right in the epicenter."
 * Phil Coulson: "I won't let you sacrifice yourself because you're scared of what's to come."
 * Daisy Johnson: "What's to come is the end of everything."
 * Melinda May: "If you can change the future here, you can change it from back home."
 * May continues to have a less scientific, more hopeful stance, simply taking each event as her current present with an undetermined future. So, in 2091, they are affecting events ("changing" from a certain perspective), so from her perspective, they can just do the same when they're back in 2017.
 * Daisy Johnson: "But we know this solution works. We can stop this today."
 * Phil Coulson: "No, it's not about today. It's about tomorrow. Even if we solve this problem, the world is never safe. The job goes on. We go on."
 * Change of scene.
 * 2091 Elena Rodriguez: "The team makes one choice, and it ruins everything."
 * 2017 Elena Rodriguez: "A choice to do what?"
 * 2091 Elena Rodriguez: "To save him."
 * We see this happen in the final episodes of the season, again implying the time loop is playing out exactly as it was for 2091 Elena, because it's the same events. This specific quote, though, isn't incompatible with the idea of just identical events going on to happen in another universe.
 * 2017 Elena Rodriguez: "What do you mean?"
 * Change of scene.
 * Phil Coulson: "Please."
 * Daisy Johnson: "Maybe I don't go with you. You know it's the right move. Coulson, as an agent of S.H.I.E.L.D., you trained me to fight. Now I'm making my stand, here."
 * Phil Coulson: "May trained you to fight... I need you to lead."
 * 2091 Elena Rodriguez: "Phil Coulson is dying. And you have to let him."
 * 2017 Elena Rodriguez: "Coulson... How? How does he die?"
 * 2091 Elena Rodriguez: "It's already begun. He's sick, and he knows it."
 * 2091 Elena should only be able to know Coulson is already sick and dying if it's a time loop. If this were simply a Coulson from a different universe to hers, then things could very well be different. She knows these things because she's been through them herself when she was the person standing in front of her. Now, yes, it's possible that she is just mistaken into thinking it's a time loop and nothing has indicated otherwise, and it's an identical universe with identical events, so Coulson does indeed happen to be sick. But that's not what the writers are presenting, and as mentioned, it would be highly unlikely that 2091 Elena would not get an indicator that it's not a time loop.
 * 2091 Elena Rodriguez: "We tried to stop it. Loyalty, it cost us the world."
 * Again, we see this event playing out in later episodes, presented as 2091 Elena knowing what will happen because it's happened to her, because it's all the same Elena. Same things about how it's possible for identical events and a mistake, but it's highly unlikely and not how it's presented.
 * 2017 Elena Rodriguez: "You heard all this, and still you couldn't change anything?"
 * 2091 Elena heard what 2091 Elena says when she was 2017 Elena, which is that way because it's a time loop. 2091 Elena didn't just hear another version of Elena in 2091, she "heard all this", as in she heard this conversation. Yes, you can fudge it that she just heard "all of this sort of thing in a very similar way", but the writers are presenting it as being literally the same conversation.
 * 2091 Elena Rodriguez: "I know. Stuck in the loop."
 * Again, in a time loop, not a chain of universes (if Elena is correct, but this nonetheless communicates the writers' intent).
 * 2091 Elena Rodriguez: "But you can forge a different fu- Even as I say the words, I realize I've heard them before."
 * This frustration is a good example of the mechanics of a time loop. Every single word Elena speaks is the same thing she heard when she was younger, because it's the same conversation. She heard herself say "But you can forge a different fu-" and then realise, "Even as I say the words, I realize I've heard them before" and say that aloud, likely realising as she says that that she's heard it before, and so on. She can try every moment to say something different to what she heard but whatever she does, it is unavoidable, because what she saw was this conversation. If what she saw was in another universe, with a chain of universes, then she would be able to break away and say even one word differently, not bound by the fact that it is literally the same conversation.
 * 2017 Elena Rodriguez: "Are you telling me to go back and change the world, or are you warning me that I can't?"
 * This is the dilemma, in summary. Hoping that time can in some way be changed, but semi-resigning to the fact that it's probably not possible and there's no clear method to somehow change it, which would only be this way if it's the same universe and timeline.
 * Again, "change", not just prevent in some other universe.
 * 2091 Elena Rodriguez: "You need to go. They're coming."
 * 2017 Elena Rodriguez: "No, not yet."
 * 2091 Elena Rodriguez: "I hope you travel a path to a world I've never seen. Now go."
 * They hold out a little hope still that maybe, just maybe, something can be done to change things.

Quote
[...] [...] [...] [...] [...] [...]
 * Elena Rodriguez: "Why are we still in the Lighthouse?"
 * Alphonso Mackenzie: "Maybe Flint's monolith didn't work."
 * Melinda May: "So we find him, try again."
 * Leo Fitz: "No, it worked. It takes you through time, but to the same place - I've been here before, with Enoch. We made it."
 * Leo Fitz: "Hunter and I left the Zephyr cloaked just outside of town. I'll show you where it is."
 * Deke Shaw: "I'm from the future."
 * Alphonso Mackenzie: "We're gonna change the future anyway."
 * Daisy Johnson: "You people literally kidnapped us and then took us to another time."
 * Piper: "So, where on Earth were you hiding?"
 * Alphonso Mackenzie: "Well, technically, it was Earth."
 * Elena is carried, her arms just sliced off, like 2091 Elena's had been.
 * Elena Rodriguez: "It's all coming true."

Dissecting

 * Elena Rodriguez: "Why are we still in the Lighthouse?"
 * Alphonso Mackenzie: "Maybe Flint's monolith didn't work."
 * Melinda May: "So we find him, try again."
 * Leo Fitz: "No, it worked. It takes you through time, but to the same place."
 * This is a discussion again about how the White Monolith merely transports you through time. There is no parallel universe involved.
 * Leo Fitz: "I've been here before, with Enoch. We made it."
 * Fitz has been here before. Not an alternate universe's identical version of here, just "here" (if Fitz is correct, but this nonetheless communicates the writers' intent).
 * Leo Fitz: "Hunter and I left the Zephyr cloaked just outside of town. I'll show you where it is."
 * Fitz knows Zephyr One is parked nearby, because he and Hunter parked it. Not that, back in his universe, he and Hunter left the Zephyr cloaked nearby, and luckily this universe's Hunter and Fitz (shown in Rewind) also did the exact same thing. "Hunter and I left the Zephyr." The Zephyr, the Zephyr of this universe, was left by "I", this Fitz (with Hunter). Yes, it's possible Fitz is just mistaken and, luckily, this universe was the same, but that is not what the dialogue has been written to say.
 * Deke Shaw: "I'm from the future."
 * Another comment about the future.
 * Alphonso Mackenzie: "We're gonna change the future anyway."
 * Mack is hopeful that they can change things, but they key word is "change". They are not fighting to prevent the future they saw from playing out in their universe, they are fighting because it is currently going to happen in their universe and they have to change it in some fashion. Yes, Mack may just be mistaken, but the agents, outside of those who do and don't necessarily agree with Fitz that time is fixed, are still nonetheless taking the fact that it is the future and just needs changing as a given. That that is the baseline fact they can at least all agree on.
 * Daisy Johnson: "You people literally kidnapped us and then took us to another time."
 * Another comment about travelling through time, just time, nothing else (not universes).
 * Piper: "So, where on Earth were you hiding?"
 * Alphonso Mackenzie: "Well, technically, it was Earth."
 * It was Earth. The point of the comment is that it wasn't the location that was the problem, it was the time. The location is the same (broadly speaking), it was the same planet, just in the future. Not an a different location as well as a different time, just a different time, so not an alternate universe's Earth in 2091, just Earth in 2091.
 * Elena is carried, her arms just sliced off, like 2091 Elena's had been.
 * Elena Rodriguez: "It's all coming true."
 * Elena is scared about the fact that, already, events are happening to lead to the future they've just been to. Her arms have been sliced off, just as they were for the older version of herself. The worry is the fact that this serves as more proof that time cannot be changed, in a fixed loop.

Quote

 * Elena Rodriguez: "We have to stay and fight. The things I heard in the future they're all coming true. Faster than imagined."

Dissecting

 * Elena Rodriguez: "We have to stay and fight. The things I heard in the future they're all coming true. Faster than imagined."
 * Another comment about the future.
 * Again, things are playing out exactly the way they were always set to play out.

Quote
[...] [...]
 * Alphonso Mackenzie: "So, we need more gravitonium to seal the rift for good, right?"
 * Leo Fitz: "Yeah, but that's something we haven't seen on this side of the future in a long time."
 * Elena Rodriguez: "What I saw, what I heard... that's all happening. There's no future but the one I saw."
 * Jemma Simmons: "No, that's not true. Hey! We can change it. We will change it."
 * Elena Rodriguez: "No. Nothing's gonna change it."
 * Elena Rodriguez: "I'm just trying to not lose faith. We're gonna change things."
 * Jemma Simmons: "That's the spirit."

Dissecting

 * Alphonso Mackenzie: "So, we need more gravitonium to seal the rift for good, right?"
 * Leo Fitz: "Yeah, but that's something we haven't seen on this side of the future in a long time."
 * Another comment about the future.
 * Elena Rodriguez: "What I saw, what I heard... that's all happening. There's no future but the one I saw."
 * Everything is pointing, for Elena, to the fact that time cannot be changed, and that's the future. That's the only future.
 * Jemma Simmons: "No, that's not true. Hey! We can change it. We will change it."
 * Elena Rodriguez: "No. Nothing's gonna change it."
 * Again, the only optimistic stance for the agents is to "change" the future, not to prevent it from happening. It is a given, for all of them, that that is the future, just they're hoping to change it.
 * Elena Rodriguez: "I'm just trying to not lose faith. We're gonna change things."
 * Jemma Simmons: "That's the spirit."
 * Again, they're hoping to "change" things, the fact that it's due to happen as things stand is a given.

Quote
[...]
 * Elena Rodriguez: "Nothing's going to happen to me."
 * Alphonso Mackenzie: "You're damn right nothing's gonna happen to you. Not on my watch."
 * Elena Rodriguez: "No, Mack. Nothing can happen to me."
 * Alphonso Mackenzie: "What's that supposed to mean?"
 * Elena Rodriguez: "Well, think about it. You saw me in the Lighthouse. You know I make it to that point in the future. Nothing can happen to me until then."
 * Alphonso Mackenzie: "You just lost both your arms. That's not nothing."
 * Elena Rodriguez: "But I didn't die."
 * Alphonso Mackenzie: "And the future we saw isn't guaranteed. We're actively working to make sure it doesn't come true, that means you could still die. I could still lose you. What then?"
 * Elena Rodriguez: "Well, then, we would have broken the loop."
 * Jemma Simmons: "It's such a confusing, grey area, but if we are going to change the timeline, we have to do things differently, make harder choices."

Quote

 * Elena Rodriguez: "Nothing's going to happen to me."
 * Alphonso Mackenzie: "You're damn right nothing's gonna happen to you. Not on my watch."
 * Elena Rodriguez: "No, Mack. Nothing can happen to me."
 * Alphonso Mackenzie: "What's that supposed to mean?"
 * Elena Rodriguez: "Well, think about it. You saw me in the Lighthouse. You know I make it to that point in the future. Nothing can happen to me until then."
 * This is another example of the time loop. Elena can't die until at least 2022 because they know she survived until at least 2022. She survived until at least 2022 because she doesn't die until at least 2022. She won't die until at least 2022 because she survived until at least 2022. She survived until at least 2022 because she doesn't die until at least 2022, etc.. This only works in a time loop, as otherwise there is nothing preventing her from dying (not that there's anything preventing her dying per se in a time loop, more just that it's knowledge that she simply won't). She could absolutely just die. It's possible she's merely mistaken, but it's not what the writers are presenting.
 * Alphonso Mackenzie: "You just lost both your arms. That's not nothing."
 * Elena Rodriguez: "But I didn't die."
 * Alphonso Mackenzie: "And the future we saw isn't guaranteed."
 * Mack believes that future is not guaranteed, for whatever reason - that they can change it, or they can prevent it, or something. He is optimistic, though his exact hope is not spelled out here.
 * Alphonso Mackenzie: "We're actively working to make sure it doesn't come true, that means you could still die. I could still lose you. What then?"
 * Elena Rodriguez: "Well, then, we would have broken the loop."
 * The reason this is significant is because it would mean they are no longer bound by predestination if Elena dies sooner than she should. If this were simply a different universe to the 2091 they visited, then if Elena died now, then that would just be a tragedy that has happened in this version of events. However, in a time loop, if Elena dies, that means they're no longer bound by the loop and no longer have no scientific chance of being successful in saving the world. Elena's comment only has significance in a time loop.
 * Jemma Simmons: "It's such a confusing, grey area, but if we are going to change the timeline, we have to do things differently, make harder choices."
 * Again, the agents are taking it as given that the timeline is set this way, that the only hope of a good future is to "change the timeline". There is no question of "But what if we're in a different universe with a chance of making sure things play out differently in this one?"

Quote
[...] [...]
 * Phil Coulson: "We traveled to the future. We saw the aftermath of that program."
 * Hale: "You traveled to the future?"
 * Phil Coulson: "And back."
 * Ruby Hale: "Did you actually travel to the future? 'Cause my mom doesn't believe that."
 * Phil Coulson: "Well aware how crazy it sounds."
 * Ruby Hale: "So, if you really did see the future, then... tell me how I fail."
 * Phil Coulson: "What do you mean?"
 * Ruby Hale: "You told my mom that the Destroyer of Worlds cracks the planet apart, so what did I do wrong?"
 * Phil Coulson: "I hate to burst your apocalyptic bubble, but it wasn't you."
 * Jemma Simmons: "Is something wrong?"
 * Alphonso Mackenzie: "Just that, lately, she's been acting like she's bulletproof, like nothing can stop her."
 * Jemma Simmons: "Well, that is not an uncommon attitude for our team."
 * Alphonso Mackenzie: "No, this is different. Yo-Yo saw herself in the Lighthouse, so now she knows for a fact that she lives far into the future."
 * Jemma Simmons: "So, if Yo-Yo subscribes to Fitz's theory that time can't be changed, then..."
 * Alphonso Mackenzie: "She thinks she can't be killed."
 * Jemma Simmons: "Interesting."

Dissecting

 * Phil Coulson: "We traveled to the future. We saw the aftermath of that program."
 * Another comment about the future.
 * They saw the aftermath of the Destroyer of Worlds program, of what's happening currently. Again, the writers are presenting the 2091 events as the future, not a parallel universe's.
 * Hale: "You traveled to the future?"
 * Phil Coulson: "And back."
 * Another comment about the future.
 * Ruby Hale: "Did you actually travel to the future? 'Cause my mom doesn't believe that."
 * Phil Coulson: "Well aware how crazy it sounds."
 * Another comment about the future.
 * Ruby Hale: "So, if you really did see the future, then... tell me how I fail."
 * Phil Coulson: "What do you mean?"
 * Ruby Hale: "You told my mom that the Destroyer of Worlds cracks the planet apart, so what did I do wrong?"
 * Phil Coulson: "I hate to burst your apocalyptic bubble, but it wasn't you."
 * The significance of this conversation is that the reason it wasn't Ruby was because it was Daisy. If it had been Ruby, then it would have been "you". This again suggests a singular universe and timeline, because if it were another universe, it wouldn't have been "you", the Ruby he's speaking to, anyway (if Coulson is correct, but this nonetheless communicates the writers' intent).
 * Jemma Simmons: "Is something wrong?"
 * Alphonso Mackenzie: "Just that, lately, she's been acting like she's bulletproof, like nothing can stop her."
 * Jemma Simmons: "Well, that is not an uncommon attitude for our team."
 * Alphonso Mackenzie: "No, this is different. Yo-Yo saw herself in the Lighthouse, so now she knows for a fact that she lives far into the future."
 * Elena knows "for a fact" that she survives into the future, since she found out in the future that she survives that long. This implies that the agents know "for a fact" that that is the future, not another universe's future, further negating the point that the agents might simply be mistaken.
 * Jemma Simmons: "So, if Yo-Yo subscribes to Fitz's theory that time can't be changed, then..."
 * They know "for a fact" that they were in the future, and the only way that that would end up not true, that Elena would be vulnerable, would be if they "changed" "time" in some fashion.
 * Alphonso Mackenzie: "She thinks she can't be killed."
 * Jemma Simmons: "Interesting."
 * Simmons is intrigued by this, realising, we later find out, that the science is sound and indeed, she shouldn't be able to die.

Quote
[...] [...] [...] [...] [...] [...] [...]
 * Deke Shaw: "And this place, 80 years from now, I'd survived on moves like that."
 * Jemma Simmons: "Can I pick your brain for a minute?"
 * Deke Shaw: "That's a weird saying."
 * Jemma Simmons: "I was hoping you could tell me more about our future."
 * Deke Shaw: "I mean, you saw it. It sucked."
 * Jemma Simmons: "No, I mean Fitz and me. Do you recall any evidence of major injury, any noticeable scarring, perhaps?"
 * Deke Shaw: "I don't remember you guys at all. I didn't even know your real names. Everyone in S.H.I.E.L.D. changed them when they were getting hunted down. I just knew you as Nana and Bobo. But you guys made it to the Lighthouse."
 * Jemma Simmons: "Good to hear."
 * Deke Shaw: "Mom talked about you a lot, but she never mentioned any health stuff. Pretty sure you were tip-top. You remind me of her. If you want, I could tell you stories about what you're a-"
 * Jemma Simmons: "I think it's best not to know too much. It's enough to know Fitz and I live long enough to create her."
 * Jemma Simmons: "Mack said you believe you can't die."
 * Elena Rodriguez: "I know it sounds crazy, Jemma, bu-"
 * Jemma Simmons: "I don't think it's crazy. I believe it's true."
 * Elena Rodriguez: "I'm glad someone understands."
 * Jemma Simmons: "I don't just mean you."
 * Elena looks at Fitz, and he gives a wry smile, as Jemma is referring to him and herself.
 * Elena Rodriguez: "You guys didn't see yourselves in the future."
 * Jemma Simmons: "No. Deke is our proof. His mother... was our daughter."
 * Elena Rodriguez: "Deke..."
 * Jemma Simmons: "Is our grandson."
 * Elena Rodriguez: "Wow. I'm sorry."
 * Leo Fitz: "Thank you."
 * Jemma Simmons: "No, no, he's really quite sweet."
 * Elena Rodriguez: "Well, it makes as much sense as anything else. So we're the invincible three, huh? Now what?"
 * Elena Rodriguez: "I saw myself alive in the future. I want to use that to help..."
 * Alphonso Mackenzie: "Damn it, Elena! That doesn't make you bulletproof. I thought you let go of that."
 * Elena Rodriguez: "There are things I can't let go of. Things I learned in the future about this team, about Coulson, about you."
 * Alphonso Mackenzie: "I don't want to hear about the future! Look, all I know is, right here, right now, you're in front of me. Safe."
 * Elena Rodriguez: "You can't protect me forever, Mack."
 * Alphonso Mackenzie: "Did you ever stop to think maybe you're alive in the future because I did? No, Fitz stays where he is. And so do you."
 * Polly Hinton: "She can see the future, and I don't even have the power to know what she's feeling."
 * Robin wanders the plane.
 * Polly Hinton: "At least when she would draw, I'd have a window into her world."
 * Daisy Johnson: "Do you remember what her last drawing was?"
 * Polly Hinton: "I have it."
 * Polly hands Daisy the drawing.
 * Polly Hinton: "Do you know what it means?"
 * Daisy has a personal flashback to Robin's death.
 * Daisy Johnson: "I'm not sure."
 * Robin gets to the cockpit, where May is.
 * Robin Hinton: "Mom? Mommy?"
 * She hugs May.
 * Robin Hinton: "I missed you. I told you Flint would get you back!"
 * Melinda May: "You did! You were right."
 * Alphonso Mackenzie: "What the hell is this?"
 * Jemma Simmons: "An experiment. The test of a hypothesis. If that hypothesis is true, you'll see that you should let Fitz out."
 * Alphonso Mackenzie: "I already gave you my answer on that."
 * Jemma Simmons: "Yeah, but we want you to reconsider with all the facts, so, I'm going to prove that I can't be killed."
 * Alphonso Mackenzie: "What, you, too, Simmons? Do you know how all this sounds?"
 * Jemma Simmons: "Like science."
 * Alphonso Mackenzie: "No. Sounds like you're detached from reality."
 * Leo Fitz: "Don't look at me. I don't know what she's doing."
 * Jemma Simmons: "Well, what's an experiment without a little scepticism? So, each of these beakers contain a liquid. Three of them contain water, the fourth holds a phosphoric acid compound used in the hydraulics of Yo-Yo's arms. Highly toxic. One sip will make you sick, I mean, this much will surely kill you."
 * Leo Fitz: "What the hell? Jemma... No."
 * Jemma Simmons: "Yes, Fitz. I wouldn't be doing this if the science wasn't sound. So, without knowing which is which, I will drink three of them, and since I can't be killed, I will happen to consume the three that just hold water."
 * Alphonso Mackenzie: "This is insane."
 * Elena shuffles the beakers.
 * Elena Rodriguez: "No looking."
 * Jemma Simmons: "I'm not looking."
 * Alphonso Mackenzie: "Are you kidd- Simmons! Are you serious?"
 * Elena Rodriguez: "Ready."
 * Alphonso Mackenzie: "Don't do it."
 * Leo Fitz: "He's right. Jemma, J-"
 * Simmons starts drinking from the first beaker.
 * Alphonso Mackenzie: "Don't. Don't. Simm- d-!"
 * Simmons finishes drinking from the first beaker.
 * Alphonso Mackenzie: "Simmons - Simmons, I need you to stop right now!"
 * Simmons starts drinking from the second beaker.
 * Leo Fitz: "N-! Oh, geez."
 * Simmons finishes drinking from the second beaker.
 * Jemma Simmons: "I will now drink the last one. And it will be water."
 * Leo Fitz: "No."
 * Alphonso Mackenzie: "No."
 * Jemma Simmons: "You would shoot me just to keep me from dying?"
 * Alphonso Mackenzie: "No, I - I'll wound you to stop this madness."
 * Jemma Simmons: "No. I don't think you will."
 * Alphonso Mackenzie: "Simmons, please. Please, Simmons, please don't."
 * Leo Fitz: "Jemma!"
 * Simmons starts drinking from the third beaker.
 * Alphonso Mackenzie: "Stop!"
 * Simmons finishes drinking from the third beaker. She gasps, seemingly feeling its effects.
 * Jemma Simmons: "Fitz..."
 * Simmons starts coughing.
 * Leo Fitz: "Jemma?"
 * Simmons falls and starts writhing.
 * Leo Fitz: "Jemma?! Jemma!"
 * Simmons is seemingly dying.
 * Alphonso Mackenzie: "Simmons! Fitz! Fitz, what do I do?!"
 * Leo Fitz: "She needs some alkaloid phosphate to counteract the toxicity!"
 * Alphonso Mackenzie: Okay, well where do I find it?!"
 * Leo Fitz: "I know where it is! Let me out!"
 * Elena Rodriguez: "Let him out! Please, let him out!"
 * Mack lets him out.
 * Leo Fitz: "Hang on, Jemma!"
 * Alphonso Mackenzie: "Hurry up!"
 * Elena speeds Mack into the cell and shuts the door.
 * Alphonso Mackenzie: "Elena, open the door! Now! Open the door! Open the door now! Ele-"
 * Simmons gets up. Mack and Fitz realise she was faking to trick Mack.
 * Leo Fitz: "A heads-up would've been nice. You sca-... Here."
 * Fitz pulls Simmons into a hug.
 * Leo Fitz: "Compliments on the performance, Dame Judi Dench. That's the longest you ever kept a lie going."
 * Jemma Simmons: "It wasn't all a lie, Fitz."
 * Simmons pours out the fourth beaker, and it fizzes on the tray, being the phosphoric acid compound.
 * Jemma Simmons: "I might've chosen that one. I didn't. Because we are invincible."
 * Leo Fitz: "And crazy, apparently."
 * Alphonso Mackenzie: "Let me out of here."
 * Elena Rodriguez: "I'm sorry, Mack. I know you don't understand. But I'm doing this to keep you safe."
 * Alphonso Mackenzie: "You're right. I don't understand."
 * Elena Rodriguez: "If, for some reason, I don't come back, it means..."
 * Jemma Simmons: "We've broken the time loop."
 * Leo Fitz: "You know my feelings on that. It can't be broken."
 * Jemma Simmons: "Oh, is that what you'd tell our daughter, that her world can't be changed?"
 * Leo Fitz: "Maybe. Don't know. Haven't met her yet."
 * Jemma Simmons: "Oh, for goodness' sake."
 * Leo Fitz: "So maybe when I..."
 * Elena Rodriguez: "Guys!"
 * Leo Fitz: "... clear it..."
 * Jemma Simmons: "Can you..."
 * Leo Fitz: "... up..."
 * Jemma Simmons: "... not..."
 * Leo Fitz: "... then..."
 * Elena Rodriguez: Guys! You'll argue on the way. But if you really believe that, Fitz, then it means we're in no dang-"
 * Elena accidentally shoots the gun in her hand in their direction, but it miraculously misses both of them.
 * Elena Rodriguez: "Lo siento [sorry]. Lo siento [sorry], lo siento [sorry]. I'm just getting used to my fingers."
 * Fitz bends to get the gun.
 * Leo Fitz: "I'll get that."
 * Elena Rodriguez: "That was close."
 * Simmons is emboldened by another survival against the odds.
 * Jemma Simmons: "Let's go."
 * May walks to Robin with her sad drawing.
 * Melinda May: "Robin, is this why you had stopped drawing before? Because of what it shows?"
 * Robin shrugs.
 * Melinda May: "We are going to try to make sure that this future never happens, okay? And to do that, we have to find..."
 * Robin Hinton: "Phillip J. Coulson. He can put all the pieces together."
 * Deke Shaw: "Well, once again, my life depends on a crayon drawing of a crazy person, which is... great for me. Is May still with her?"
 * Daisy Johnson: "Yeah. I just cannot imagine bouncing back and forth between the past and the future like that. It sounds terrible."

Dissecting

 * Deke Shaw: "And this place, 80 years from now, I'd survived on moves like that."
 * Deke was surviving in "this place", 73 years from now (he's rounding since it's 8 decades, 2010s to 2090s). So this place, plus 73 years, is the dystopian 2091 where Deke was living, making this the same universe and timeline. If not, then "this place, [73] years from now" would not at all be where Deke was living, a completely different future already, because the future would already be set to be positive. You can't rewrite a timeline as you go, the future is always going to be the way it is, the only hope for "change" is to branch a timeline. So the future, where they stand, is the dystopian 2091 they visited.
 * Jemma Simmons: "Can I pick your brain for a minute?"
 * Deke Shaw: "That's a weird saying."
 * Jemma Simmons: "I was hoping you could tell me more about our future."
 * "Our" future. Not the future of her and Fitz's alternate selves, but just simply her and Fitz's future, which Deke knows about, being from their future.
 * Deke Shaw: "I mean, you saw it. It sucked."
 * What they saw was "our" future, not another future.
 * Jemma Simmons: "No, I mean Fitz and me. Do you recall any evidence of major injury, any noticeable scarring, perhaps?"
 * Deke Shaw: "I don't remember you guys at all. I didn't even know your real names. Everyone in S.H.I.E.L.D. changed them when they were getting hunted down. I just knew you as Nana and Bobo. But you guys made it to the Lighthouse."
 * Jemma Simmons: "Good to hear."
 * Deke Shaw: "Mom talked about you a lot, but she never mentioned any health stuff. Pretty sure you were tip-top. You remind me of her. If you want, I could tell you stories about what you're a-"
 * Jemma Simmons: "I think it's best not to know too much. It's enough to know Fitz and I live long enough to create her."
 * Simmons now knows that they live long enough to have a daughter, because Deke knows they lived long enough to have a daughter, which only works if it's a time loop.
 * Jemma Simmons: "Mack said you believe you can't die."
 * Elena Rodriguez: "I know it sounds crazy, Jemma, bu-"
 * Jemma Simmons: "I don't think it's crazy. I believe it's true."
 * As Simmons was discussing with Mack, when subscribing to the idea that time can't be changed, then Elena cannot die in 2018, because they have knowledge that she survives 2018 in the timeline - only working if that were the same timeline.
 * Elena Rodriguez: "I'm glad someone understands."
 * Jemma Simmons: "I don't just mean you."
 * Elena looks at Fitz, and he gives a wry smile, as Jemma is referring to him and herself.
 * Elena Rodriguez: "You guys didn't see yourselves in the future."
 * Another comment about the future, and how that is what's significant for this idea of not being able to die - that they have to know from the future.
 * Jemma Simmons: "No. Deke is our proof. His mother... was our daughter."
 * Deke's mother is their daughter. Not another Fitz and Simmons', theirs, so he's from the future of this universe and timeline.
 * Elena Rodriguez: "Deke..."
 * Jemma Simmons: "Is our grandson."
 * He's their grandson, not another Fitz and Simmons', theirs, so he's from the future of this universe and timeline.
 * Elena Rodriguez: "Wow. I'm sorry."
 * Leo Fitz: "Thank you."
 * Jemma Simmons: "No, no, he's really quite sweet."
 * Elena Rodriguez: "Well, it makes as much sense as anything else. So we're the invincible three, huh? Now what?"
 * They know themselves to be, in a sense, invincible. Not in the sense that they're physically unable to be killed, but the fact that they simply have the knowledge that they don't die for years to come, meaning they won't die for years to come, so whatever they do, despite the odds, they just must survive. Only works under a time loop.
 * Elena Rodriguez: "I saw myself alive in the future. I want to use that to help..."
 * Another comment about the future.
 * Alphonso Mackenzie: "Damn it, Elena! That doesn't make you bulletproof. I thought you let go of that."
 * As discussed above, Elena knows she won't die, but isn't physically bulletproof. Mack, worried for her, looks at it the latter way.
 * Elena Rodriguez: "There are things I can't let go of. Things I learned in the future about this team, about Coulson, about you."
 * Another comment about the future.
 * Alphonso Mackenzie: "I don't want to hear about the future! Look, all I know is, right here, right now, you're in front of me. Safe."
 * Elena Rodriguez: "You can't protect me forever, Mack."
 * Alphonso Mackenzie: "Did you ever stop to think maybe you're alive in the future because I did? No, Fitz stays where he is. And so do you."
 * Mack's comment about her possibly only surviving because he advised caution is another example of a casual loop paradox, only working under a causal loop. He is positing, if she had listened to him: In 2018, Elena wants to be reckless, which likely would have got her killed. However, Mack cautioned her, which led to her surviving for years. Because she survived for years, she later found out she survived for years. Because she found out she survived for years, in 2018, Elena wants to be reckless, which likely would have got her killed. However, Mack cautioned her, which led to her surviving for years, etc.. He is specifically referring to her being alive in the future, not just that the version of her that they saw perhaps only survived in that universe because of the parallel version of him cautioning her.
 * Polly Hinton: "She can see the future, and I don't even have the power to know what she's feeling."
 * Robin sees the future. Everything she sees, including events from The Last Day in 2018-2022 and all the 2091 events, which she sees, are in the future of this timeline, not another one.
 * Robin wanders the plane.
 * Polly Hinton: "At least when she would draw, I'd have a window into her world."
 * Daisy Johnson: "Do you remember what her last drawing was?"
 * Polly Hinton: "I have it."
 * Polly hands Daisy the drawing.
 * Polly Hinton: "Do you know what it means?"
 * Daisy has a personal flashback to Robin's death.
 * Robin saw her 2091 death from The Last Day, meaning that's in the future of this timeline, not another one. One could argue that it's just her seeing this timeline's version of her death, identical to the one in The Last Day, but in that case it defeats the purpose of the alternate universe theory, specifically intended for the future of this universe to not be dystopian.
 * Daisy Johnson: "I'm not sure."
 * Robin gets to the cockpit, where May is.
 * Robin Hinton: "Mom? Mommy?"
 * She hugs May.
 * Robin is seeing the future, where May becomes her adoptive mother after Polly dies. This again means that the future of this universe is indeed dystopian, so there is then no reason for the dystopian future of the first half of the season to be anything other than this dystopian future, when that's how it's presented. Robin is specifically referring to the 2018-2022 scenes from The Last Day, in the future of this universe.
 * Robin Hinton: "I missed you. I told you Flint would get you back!"
 * Melinda May: "You did! You were right."
 * Robin is referring to when she, experiencing things as her elderly self, told May about Flint in 2091, in The Last Day. Therefore, that is the future of this universe. Again, if arguing that The Last Day was just an identical event in another universe, that would be pointless, since this still proves that the same event happens in this universe's future, therefore defeating the purpose of the argument in the first place, when, if this universe is set to have identical events, the events might as well be just the same ones, in this universe's future, as presented.
 * Alphonso Mackenzie: "What the hell is this?"
 * Jemma Simmons: "An experiment. The test of a hypothesis. If that hypothesis is true, you'll see that you should let Fitz out."
 * Alphonso Mackenzie: "I already gave you my answer on that."
 * Jemma Simmons: "Yeah, but we want you to reconsider with all the facts, so, I'm going to prove that I can't be killed."
 * Alphonso Mackenzie: "What, you, too, Simmons? Do you know how all this sounds?"
 * Jemma Simmons: "Like science."
 * Again, for the same reasons, the science means that they cannot die in 2018. This means it's a time loop. If it were another universe, then knowing they survive through 2018 in that universe wouldn't cause any science to support the idea that they can't die now (if Simmons is correct, but this nonetheless communicates the writers' intent).
 * Alphonso Mackenzie: "No. Sounds like you're detached from reality."
 * Leo Fitz: "Don't look at me. I don't know what she's doing."
 * Jemma Simmons: "Well, what's an experiment without a little scepticism? So, each of these beakers contain a liquid. Three of them contain water, the fourth holds a phosphoric acid compound used in the hydraulics of Yo-Yo's arms. Highly toxic. One sip will make you sick, I mean, this much will surely kill you."
 * Leo Fitz: "What the hell? Jemma... No."
 * Jemma Simmons: "Yes, Fitz. I wouldn't be doing this if the science wasn't sound."
 * Simmons is confident in the science, that it's a time loop.
 * Jemma Simmons: "So, without knowing which is which, I will drink three of them, and since I can't be killed, I will happen to consume the three that just hold water."
 * Jemma only has a (0.25 × 0.33333 × 0.5 + 0.25 × 0.33333 × 0.5 + 0.25 × 0.33333 × 0.5 + 0.25 × 0.33333 × 0.5 + 0.25 × 0.33333 × 0.5 + 0.25 × 0.33333 × 0.5) 25% chance of survival, speaking simply about unfolding events, in picking three of the four beakers, and them all being safe. Except from her perspective, she has a 100% chance of getting that 25% chance outcome because she knows she gets it. It's like getting a glimpse into the future of next week's lottery numbers, a 1 in a million chance simply speaking, but from your perspective, you have a 100% chance of getting that 1 in a million chance. If this were a different universe, then she's just lucky, getting the 25% odds of success. In a time loop, there is more to it, as it's luck from one perspective but certainty from another, and the time loop establishes a paradox wherein she can't die, and it can be looked at the other way around: while yes, she makes it past 2018 in part because she survives here, she also survives here because she has to make it past 2018. It's a "chicken and the egg" situation, does she succeed at her 25% chance which gives her a 100% chance, or does she have a 100% chance meaning she succeeds at her 25% chance? She simultaneously has a 25% chance and 100% chance, rather than just a normal 25% chance.
 * Alphonso Mackenzie: "This is insane."
 * Elena shuffles the beakers.
 * Elena Rodriguez: "No looking."
 * Jemma Simmons: "I'm not looking."
 * Alphonso Mackenzie: "Are you kidd- Simmons! Are you serious?"
 * Elena Rodriguez: "Ready."
 * Alphonso Mackenzie: "Don't do it."
 * Leo Fitz: "He's right. Jemma, J-"
 * Simmons starts drinking from the first beaker.
 * Alphonso Mackenzie: "Don't. Don't. Simm- d-!"
 * Simmons finishes drinking from the first beaker.
 * Alphonso Mackenzie: "Simmons - Simmons, I need you to stop right now!"
 * Simmons starts drinking from the second beaker.
 * Leo Fitz: "N-! Oh, geez."
 * Simmons finishes drinking from the second beaker.
 * Jemma Simmons: "I will now drink the last one. And it will be water."
 * Leo Fitz: "No."
 * Alphonso Mackenzie: "No."
 * Jemma Simmons: "You would shoot me just to keep me from dying?"
 * Alphonso Mackenzie: "No, I - I'll wound you to stop this madness."
 * Jemma Simmons: "No. I don't think you will."
 * Alphonso Mackenzie: "Simmons, please. Please, Simmons, please don't."
 * Leo Fitz: "Jemma!"
 * Simmons starts drinking from the third beaker.
 * Alphonso Mackenzie: "Stop!"
 * Simmons finishes drinking from the third beaker. She gasps, seemingly feeling its effects.
 * Jemma Simmons: "Fitz..."
 * Simmons starts coughing.
 * Leo Fitz: "Jemma?"
 * Simmons falls and starts writhing.
 * Leo Fitz: "Jemma?! Jemma!"
 * Simmons is seemingly dying.
 * Alphonso Mackenzie: "Simmons! Fitz! Fitz, what do I do?!"
 * Leo Fitz: "She needs some alkaloid phosphate to counteract the toxicity!"
 * Alphonso Mackenzie: Okay, well where do I find it?!"
 * Leo Fitz: "I know where it is! Let me out!"
 * Elena Rodriguez: "Let him out! Please, let him out!"
 * Mack lets him out.
 * Leo Fitz: "Hang on, Jemma!"
 * Alphonso Mackenzie: "Hurry up!"
 * Elena speeds Mack into the cell and shuts the door.
 * Alphonso Mackenzie: "Elena, open the door! Now! Open the door! Open the door now! Ele-"
 * Simmons gets up. Mack and Fitz realise she was faking to trick Mack.
 * Leo Fitz: "A heads-up would've been nice. You sca-... Here."
 * Fitz pulls Simmons into a hug.
 * Leo Fitz: "Compliments on the performance, Dame Judi Dench. That's the longest you ever kept a lie going."
 * Jemma Simmons: "It wasn't all a lie, Fitz."
 * Simmons pours out the fourth beaker, and it fizzes on the tray, being the phosphoric acid compound.
 * Jemma Simmons: "I might've chosen that one. I didn't. Because we are invincible."
 * Despite the ruse, the experiment was still happening as intended, and despite the odds, Simmons survived. It's possible that she just survived due to luck (and, as explained above, there's an argument to be made that even in a time loop, she's still technically just surviving due to luck), but it's presented that she survived because that's the science, as she says. She cannot die, due to the time loop.
 * Leo Fitz: "And crazy, apparently."
 * Alphonso Mackenzie: "Let me out of here."
 * Elena Rodriguez: "I'm sorry, Mack. I know you don't understand. But I'm doing this to keep you safe."
 * Alphonso Mackenzie: "You're right. I don't understand."
 * Elena Rodriguez: "If, for some reason, I don't come back, it means..."
 * Jemma Simmons: "We've broken the time loop."
 * Again, there's a significance to one of them dying - a positive, despite the obvious negative - because it is evidence that they actually have a chance to change things. If they were in a different universe, it's just an unfortunate casualty. Sure, if they are in a different universe then clearly they still think they are in a time loop, and therefore would also mistakenly see the same significance, but again this involves assuming mistakes from the characters as well as going against what the writers are presenting.
 * Leo Fitz: "You know my feelings on that. It can't be broken."
 * Fitz reaffirms his stance again, this time instead of saying that time can't be changed, phrasing it that it would mean the time loop cannot be broken. The agents are again taking it as a given that they are in a time loop, the only question being whether they can break it or not.
 * Jemma Simmons: "Oh, is that what you'd tell our daughter, that her world can't be changed?"
 * Leo Fitz: "Maybe. Don't know. Haven't met her yet."
 * Jemma Simmons: "Oh, for goodness' sake."
 * Leo Fitz: "So maybe when I..."
 * Elena Rodriguez: "Guys!"
 * Leo Fitz: "... clear it..."
 * Jemma Simmons: "Can you..."
 * Leo Fitz: "... up..."
 * Jemma Simmons: "... not..."
 * Leo Fitz: "... then..."
 * Elena Rodriguez: Guys! You'll argue on the way. But if you really believe that, Fitz, then it means we're in no dang-"
 * Elena accidentally shoots the gun in her hand in their direction, but it miraculously misses both of them.
 * Again, the group survive despite the even lower odds. Assuming an approximate 5% chance of survival, then to survive this and Simmons' experiment becomes very unlikely without a cosmic factor. Again, with the cosmic factor of the time loop, you end up with a situation of simultaneous 100% chance of survival: do they survives in a scenario with a 5% chance of survival, which gives her a 100% chance, or do they have a 100% chance, meaning they survive in the scenario with a 5% chance?
 * Elena Rodriguez: "Lo siento [sorry]. Lo siento [sorry], lo siento [sorry]. I'm just getting used to my fingers."
 * Fitz bends to get the gun.
 * Leo Fitz: "I'll get that."
 * Elena Rodriguez: "That was close."
 * Simmons is emboldened by another survival against the odds.
 * Jemma Simmons: "Let's go."
 * Again, Simmons feels further emboldened and sure that clearly the science is correct: they are in a time loop, unable to die because of it.
 * May walks to Robin with her sad drawing.
 * Melinda May: "Robin, is this why you had stopped drawing before? Because of what it shows?"
 * Again, Robin, who sees the future, has been seeing things such as her death and other events in the dystopian future. The dystopian future is the future, of this universe.
 * Robin shrugs.
 * Melinda May: "We are going to try to make sure that this future never happens, okay?"
 * "Never happens" would imply actually rewriting time, in the way Fitz has said you can't, as Avengers: Endgame establishes you can't, and as is further disproved by Deke's continued existence. That said, May and Mack take the least scientific stance of the group, and it's likely this is just the way she sees "changing" time, still making more sense under trying to change time in some fashion than purely preventing it from being just in this universe.
 * Melinda May: "And to do that, we have to find..."
 * Robin Hinton: "Phillip J. Coulson. He can put all the pieces together."
 * See April 13, 2018 The Honeymoon for discussion of this.
 * Deke Shaw: "Well, once again, my life depends on a crayon drawing of a crazy person, which is... great for me. Is May still with her?"
 * Daisy Johnson: "Yeah. I just cannot imagine bouncing back and forth between the past and the future like that. It sounds terrible."
 * Again, Robin goes back and forth between the past and the future, meaning the dystopian 2091 is in the future, not a different universe's future, with this universe's future being positive.

Quote
[...] [...] [...] [...] [...]
 * Glenn Talbot: "Where were you?"
 * Phil Coulson: "We were in the future."
 * Deke Shaw: "Well, I thought that I left all this prophecy crap back in the future."
 * Glenn Talbot: "So, this kid's from the future?"
 * Phil Coulson: "Yeah. And in that future, Earth is gone, and the last of humanity is enslaved by alien overlords. [...] There's a young Inhuman who's seen a better future. We're working toward that."
 * Jemma Simmons: "But there's always a chance that we've tried this before."
 * Leo Fitz: "More than a chance. Previous selves probably came here, made all the same decisions still failed to change the timeline.
 * Jemma Simmons: "You spoke to your older self in the future. Did she give you any clues, any specific ways to stop this all from happening again?"
 * Elena Rodriguez: "We didn't have much time. I haven't told anyone this, not even Mack. I didn't want to put this on the team."
 * Leo Fitz: "What?"
 * Elena Rodriguez: "We have to let Coulson die."
 * Jemma Simmons: "What? That - That doesn't make sense."
 * Elena Rodriguez: "The other me, she said, trying to save him is what led to the end."
 * Jemma Simmons: "Please tell me you still believe time can't be changed."
 * Leo Fitz: "You want to debate that now? Isn't - Isn't that why we're here?"
 * Jemma Simmons: "No, Fitz, just tell me it's against the law of physics, I need that right now."
 * Leo Fitz: "The perception of time is an illusion."
 * Jemma Simmons: "Last mag."
 * Leo Fitz: "According to Hermann Minkowski, space-time -"
 * Jemma Simmons: "Oh, you know what? I was wrong, it's not helping!"
 * Jemma Simmons: "Still can't believe we survived."
 * Leo Fitz: "Me neither."
 * Jemma Simmons: "But you were so certain we'd be fine, "time is fixed" and all that."
 * Leo Fitz: "I started having my doubts. Maybe your hopeful nature is rubbing off on me."

Dissecting

 * Glenn Talbot: "Where were you?"
 * Phil Coulson: "We were in the future."
 * Another comment about the future.
 * Deke Shaw: "Well, I thought that I left all this prophecy crap back in the future."
 * Another comment about the future.
 * Glenn Talbot: "So, this kid's from the future?"
 * Another comment about the future.
 * Phil Coulson: "Yeah. And in that future, Earth is gone, and the last of humanity is enslaved by alien overlords. [...] There's a young Inhuman who's seen a better future. We're working toward that."
 * This is interesting, as it hasn't been previously mentioned that Robin can see a better future. She has only been said to be able to see the future. However, with the comment from The Last Day about Robin being right about changing time and in Inside Voices about Coulson putting the pieces together, it would seem that essentially, Robin can only experience (as her mind jumps around in time) the future of the timeline she's in, and can only clearly see the future, but can see glimpses of potential things to change the timeline, involving Coulson.
 * It would seem that the timeline should split in the future. For Robin to be able to see glimpses of changes other than the actual future she properly sees and connects with, these changes should also be in the future of this universe (splitting off).
 * Jemma Simmons: "But there's always a chance that we've tried this before."
 * Leo Fitz: "More than a chance."
 * This would again suggest a time loop, specifically they ("we've") have tried this before, from a certain perspective.
 * Leo Fitz: "Previous selves probably came here, made all the same decisions still failed to change the timeline."
 * Referring to previous selves, however, does lean more in the direction of a chain of universes. However, the fact that Fitz is still talking about wanting to "change the timeline" would suggest just talking about changing events for one universe, one timeline. It's possible that Fitz is just, again, using a figure of speech for the perspective of a time loop repeating itself in iterations.
 * Jemma Simmons: "You spoke to your older self in the future.
 * Her older self, not another version of her.
 * Jemma Simmons: "Did she give you any clues, any specific ways to stop this all from happening again?"
 * Elena Rodriguez: "We didn't have much time. I haven't told anyone this, not even Mack. I didn't want to put this on the team."
 * Leo Fitz: "What?"
 * Elena Rodriguez: "We have to let Coulson die."
 * Jemma Simmons: "What? That - That doesn't make sense."
 * Elena Rodriguez: "The other me, she said, trying to save him is what led to the end."
 * Elena calls 2091 Elena "the other me", suggesting more of a separate person than just her in the future. However, it's very possible she is just speaking loosely, the other Elena who was present in that room.
 * Jemma Simmons: "Please tell me you still believe time can't be changed."
 * Jemma wants a reminder that time can't be changed, because they're in danger, and this would mean again that they cannot die.
 * Leo Fitz: "You want to debate that now? Isn't - Isn't that why we're here?"
 * Again, they are here with the hope that time can "be changed", that they can change it, not just prevent things from playing out similarly in this universe.
 * Jemma Simmons: "No, Fitz, just tell me it's against the law of physics, I need that right now."
 * Leo Fitz: "The perception of time is an illusion."
 * Jemma Simmons: "Last mag."
 * Leo Fitz: "According to Hermann Minkowski, space-time -"
 * Jemma Simmons: "Oh, you know what? I was wrong, it's not helping!"
 * Fitz again states that time is fixed, with Simmons specifically saying to rewrite time would be "against the law of physics".
 * Jemma Simmons: "Still can't believe we survived."
 * Leo Fitz: "Me neither."
 * Jemma Simmons: "But you were so certain we'd be fine, "time is fixed" and all that."
 * Again, they survive despite the odds, caught in a firefight that would almost certainly get at least one of them at least badly injured. But they're fine, the explanation being that, most likely, this is just because they were always going to be fine, because they have to turn out fine. Yes, it's possible that they're mistaken and just happen to survive all of these things, but that's not the way the writers present it, nor is it likely - with Simmons unscathed from consecutive events with a 25% chance of survival, a roughly 22.4% individual chance of survival (if going by the idea of about 5% chance that both her and Fitz are unharmed, then there should be about a 22.4% individual chance each), and then a maybe 10% chance of being unharmed in this firefight, you're looking at a 0.6% chance of Simmons' survival in the last couple of days and she's not even harmed, unless in a time loop, where she has, in a sense, a 100% chance of being OK.
 * Leo Fitz: "I started having my doubts. Maybe your hopeful nature is rubbing off on me."
 * The agents still discuss the possibility that maybe time is not "fixed", with the writers clearly planting all these mentions as factors towards the ultimate solution (not least since it is mentioned again after they succeed). Time is suggested to be changeable in a certain fashion.
 * It is not that time is indeed fixed and they're just in a different universe, it's that time maybe is not exactly fixed, changeable in a certain fashion for their universe.

Quote
[...] [...] [...] [...]
 * Ruby Hale: "Your little trip to the future? Coulson filled me in."
 * Leo Fitz: "You realise that we have a choice to make?"
 * Jemma Simmons: "Yeah. Our hypothesis is being proven. We die, we break the loop. We don't fix this, we stop them."
 * Deke Shaw: "Well, I'm not even gonna be born for another 50 years, so maybe rethink "out there"."
 * Phil Coulson: "Well, let's hope it never happens, but if we can't change things then-"
 * Alphonso Mackenzie: ""Always be prepared," yeah, yeah."
 * Glenn Talbot: "So, this is who all the fuss is about, huh? She can tell the future?"
 * Polly Hinton: "Sort of. She sees a lot, but it's all out of order."
 * Glenn Talbot: "Who is this? And when does this happen?"
 * Polly Hinton: "That's not really how it works."
 * Robin Hinton: "Soon."
 * Glenn Talbot: "Soon... And these? These all come true? We need to act on this."

Dissecting

 * Ruby Hale: "Your little trip to the future? Coulson filled me in."
 * Another comment about the future.
 * Leo Fitz: "You realise that we have a choice to make?"
 * Jemma Simmons: "Yeah. Our hypothesis is being proven. We die, we break the loop. We don't fix this, we stop them."
 * Another comment about being in a loop and wanting to break it, and that if one of them died then it would be broken and they have a chance to save the world, but they don't feel able to allow that to happen.
 * Deke Shaw: "Well, I'm not even gonna be born for another 50 years, so maybe rethink "out there"."
 * Deke is due to be born in 50 years. If they were in a new universe, that would not be the case. Another Deke might be due to be born in 50 years (and in fact wouldn't be, since they change the timeline so that the humans aren't stuck together in the Lighthouse, so it's likely Deke's parents wouldn't meet, but at this point as far as they're aware the future would still be dystopian), but not him. They have to be in the same timeline he is from for Deke to be born in 50 years' time (if Deke is correct, but this nonetheless communicates the writers' intent). It's also clear that Deke, now they have returned to 2017 (now lived through into 2018), has ditched his initial comment about how it might've been another Daisy who destroyed the world since this Daisy had been plucked out of 2017. Since they've returned, there's no need for that, and he just agrees it's the same timeline.
 * Phil Coulson: "Well, let's hope it never happens, but if we can't change things then-"
 * Alphonso Mackenzie: ""Always be prepared," yeah, yeah."
 * Again, they're concerned about whether they can "change things", not make this universe have things play out differently (if Coulson is correct, but this nonetheless communicates the writers' intent)
 * Glenn Talbot: "So, this is who all the fuss is about, huh? She can tell the future?"
 * Polly Hinton: "Sort of. She sees a lot, but it's all out of order."
 * Another discussion of Robin's powers being that she sees things from across the timeline, just out of order. Not that she can see other universes.
 * Glenn Talbot: "Who is this? And when does this happen?"
 * Polly Hinton: "That's not really how it works."
 * Robin Hinton: "Soon."
 * Glenn Talbot: "Soon... And these? These all come true? We need to act on this."
 * Everything Robin says comes true, the timeline of their universe still will be dystopian. The only way it isn't would therefore be if they, later than this, somehow split off into another timeline.
 * Their universe is going to end up dystopian soon, again meaning there is no reason for the 2091 events to have been a different universe, since this universe's future is that dystopia anyway and the main motive for assuming the 2091 they visit is a different universe is to explain the change in events. But the change in events must be some sort of splitting off and not that this universe just turns out differently, as this universe's future is indeed dystopian, only then not being when they in some fashion change it.

Quotes

 * Doctor Strange: "I went forward in time to view alternate futures. To see all the possible outcomes of the coming conflict."
 * Star-Lord: "How many did you see?"
 * Doctor Strange: "Fourteen million, six hundred and five."
 * Tony Stark: "How many did we win?"
 * Doctor Strange: "One."

Dissecting

 * Doctor Strange: "I went forward in time to view alternate futures."
 * It's unclear exactly what Strange means by "alternate futures". The fact that he specifically says "I went forward in time", though, would suggest that it was a physical exploration of these futures, not just a look at different possibilities as the rest of the quote might otherwise suggest. The phrasing would imply some sort of branches after this point in the timeline, but the exact structure and rules are left unclear.
 * Doctor Strange: "To see all the possible outcomes of the coming conflict."
 * "Possible outcomes" would suggest that these are in some way only hypothetical, not actually physically realised in some way. However, coupled with the previous sentence, "I went forward in time to view alternate futures," it would appear more that Strange is saying that he wanted to see the possible outcomes, so he went forward in time to view alternate futures. So the futures themselves are not necessarily hypothetical/not realised physically.
 * Star-Lord: "How many did you see?"
 * Doctor Strange: "Fourteen million, six hundred and five."
 * Tony Stark: "How many did we win?"
 * Doctor Strange: "One."
 * The nature of all these different "alternate futures"/"possible outcomes" raises questions about how exactly the Avengers' success in Avengers: Endgame works. Does it mean that all fourteen million, six hundred and five different futures played out in individual branching timelines and that the films have simply just decided to show the one where things played out well? That would mean that their efforts weren't particularly important, the films essentially just decided to follow the timeline where their efforts paid off and not the millions of other ones were they failed, rather than the Avengers specifically managing, with Strange's help, to make the necessary sacrifices and guide the single universe/timeline to a successful result. The fact that it is presented the latter way would suggest that the other fourteen million, six hundred and four futures in some way did not come to pass, that they are not equally valid timelines out there in the multiverse. The Russos' later comments about this help a little.

Quote
[...] [...] [...] [...]
 * Elena Rodriguez: "Well, we didn't pick you. Coulson made that decision and brought you back when he could have broken that loop right there!"
 * Deke Shaw: "... But not according to the multiverse theory."
 * Leo Fitz: "Hmm, I'm not sure you actually know what "multiverse" means."
 * Deke Shaw: "That every choice we make spins out a different timeline into the cosmos, and right now, there are infinite parallel universes. But I am proof that you can move between them."
 * Leo Fitz: "Or, you are proof that we are in one timeline, in a loop an infinite, intractable, unchangeable loop."
 * Jemma Simmons: "But, if we succeed in ridding the planet of gravitonium, then we break that loop and prevent the Earth's destruction."
 * Deke Shaw: "Which is great, because that definitely won't affect me at all. Look, it's not like I'm just gonna blink out of existence. I lived in one timeline, but now I live in this new one, and I think I'm gonna stay in the one with the sun and tacos and all that, because that's the multiverse, that's science."
 * Leo Fitz: "Or you're a canary in a coal mine."
 * Deke Shaw: "I don't know what either of those things are."
 * Leo Fitz: "We won't know if we're successful at changing the future unless you blink out of existence."
 * Jemma Simmons: "Fitz..."
 * Leo Fitz: "Jemma agrees. She actually wrote a paper on the theory of -"
 * Jemma Simmons: "Nobody knows how it works."
 * Elena Rodriguez: "You need to listen. You saw her, me in the future. I spoke to her. She warned me of all of this."
 * Alphonso Mackenzie: "I don't want to hear it, and I don't want to know."
 * Elena Rodriguez: "She was trying to help us, Mack, to prevent this. To keep me from losing you. She said things that -"
 * Alphonso Mackenzie: "Yeah, and it's making you crazy. This whole future thing has got you all acting crazy. I don't wanna know. I'm just trying to fix the problems right in front of me, not get my mind twisted trying to figure out what comes next."
 * Elena Rodriguez: "We already saw what comes next!"
 * Alphonso Mackenzie: "So you're willing to do anything, no matter who it hurts?! We've been through too much [...] In the future we swore. We swore we wouldn't lose ourselves."
 * Melinda May: "She's following a lead."
 * Phil Coulson: "A lead on what?"
 * Melinda May: A way to keep you alive.
 * Elena Rodriguez: "What?"
 * Phil Coulson: "I don't want that. My orders are very clear about that."
 * Melinda May: "If there's a chance we can save you, don't you think I'd take it?"
 * Phil Coulson: "Right now, we all need saving from our new overlords out there, and our most powerful team member's gone."
 * Elena Rodriguez: "No, no, no, no, no. I killed Ruby for nothing. It didn't matter, it's all happening, right now. Everything she told me."
 * Phil Coulson: ""She" who?"
 * Elena Rodriguez: "This, right here? This is how we lose. I could've warned myself about a lot of things. Ruby, Hale, these aliens... but instead, she told me - Instead, she told me, "Coulson is dying, and we need to let him." I'm sorry, sir. I hated keeping this. I owe you so much. You're my family."
 * Melinda May: "No, you're wrong. Robin said Coulson puts the pieces back together. And you're saying that we should've just left him to freeze to death in the middle of nowhere."
 * Elena Rodriguez: "I have to listen, May [...] She was me. She's lived through this, through the loop, who knows how many times?"
 * Melinda May: "Exactly, you don't know. We haven't lost yet, and as far as we know, they can't get in here, - and until they do [...] you better believe we're gonna do everything possible to keep him alive."
 * Alphonso Mackenzie: "Well, people in the future survive. There must be a way to stop them."
 * Deke Shaw: "No, we didn't stop them."

Dissecting

 * Elena Rodriguez: "Well, we didn't pick you. Coulson made that decision and brought you back when he could have broken that loop right there!"
 * Another comment about the loop, and how they have had opportunities to definitely change things but failed, meaning they are still stuck in the loop.
 * Deke Shaw: "... But not according to the multiverse theory."
 * To be clear, we don't see the preceding part of the conversation. The scene starts mid-conversation.
 * Leo Fitz: "Hmm, I'm not sure you actually know what "multiverse" means."
 * Deke Shaw: "That every choice we make spins out a different timeline into the cosmos, and right now, there are infinite parallel universes."
 * It would seem that Deke's essentially saying, "Okay, I agree with you, you can't rewrite the timeline, but that doesn't mean we're stuck - what if, instead, the multiverse theory is true and we manage to forge a different future, not negating the past one but nonetheless positive."
 * If Deke is correct, different timelines spin out from each timeline, and that's what creates parallel universes. The show later suggests that Deke's multiverse theory was correct, implying this too was correct.
 * With his previous comment no longer relevant, Deke nonetheless sticks to the idea of a multiverse. The show later goes on to suggest that Deke is correct, and therefore this statement is important. It would suggest that the show's stance on the multiverse is simply that all decisions spin out different timelines, and that this is what the multiverse is. Further, that would imply that when the agents manage to "change time", they are essentially at one of these spinning out points, and manage to guide their lives down the good path, and not toward the dystopian.
 * This would align with the time loop, as at every decision point, another version of them might have spun out into a new, better, branch timeline, but the show is following the agents who make the same decisions every time heading toward that dystopian future, and then going around and around in that one through-line of a timeline. And then, when the show follows the agents into a branch not headed for the dystopian future, for those agents, the loop is broken.
 * The nature of them guiding their lives down the good path, however, is unclear. If the multiverse tree is simply just that - a tree - on which one future is dystopian and one is not, then that would suggest that technically, the agents haven't changed things, just the show is choosing to instead follow into that good path, rather than the bad path, which it has otherwise been following when showing events post-2018. However, does raise a question of what extent to which the agents are exactly "successful", the same as with the Avengers and the fourteen million alternate futures. This way around would mean that they are not successful in any particular regard, just that the show and films are choosing to show us the one path where all the decisions went the certain way that was positive, while there's simultaneously many paths where everything ended up horrible. The only way to frame this positively is "But we're following the agents/Avengers who still had to make those sacrifices and the hard decisions. Just because there was always going to be a universe where things turned out OK and we happen to be following it doesn't mean that, from the people in that universe's perspective, they haven't faced the hardships to make their world this way. And if there's just infinite universes spinning off all the time, we essentially shouldn't worry about the ones we're not shown." That's not particularly satisfying though. While it's more acceptable for the agents (despite the comments that they are hoping to make sure this world "never comes to be"), who have at least given the dystopian branch universe some hope with Flint and Tess and done everything they can, while also needing that universe to still exist in some capacity for Deke to exist, it very much lessens the Avengers' victory. Plus, the whole idea of Strange going forward in time is to try to, in whatever capacity, guide things down the good route, not just go, "Well, it's out of her hands now. There will be a universe where things turn out well, and fourteen million, six hundred and four where they don't," and it would be odd for those things to also still play out exactly the same way with Strange having already seen them - if Strange were seeing futures in which he has just been looking at these futures. The Russos' comment about this later on helps.
 * The thing is, Charles and Robin Hinton's powers both involved looking specifically into the future, which doesn't line up with the idea of equally valid branches ahead. It suggests that there is a timeline. There has been a hint, as previously discussed, that Robin's powers might see potential spin-out points, but otherwise her mind jumps across the timeline, until she feels the shift in The End into a new one. This would align better with the idea of "changing" time in The End, or the Avengers' success in Avengers: Endgame, but if Deke is correct, that would mean some sort of disparity between types of branches, with a "main" line that somehow gets shifted in The End and other somehow less important ones. This does not particularly make sense scientifically, so it's possible instead that these other universes are more hypothetical universes that don't come to be unless people manage somehow to break through into them as they're burgeoning, so Deke would have the general gist correct, but not quite there. This would likely be the most satisfying fit to all the statements, especially since a problem with the idea of shifting a "main" line doesn't really make sense, as if you were looking at a diagram of a timeline and could highlight one line, and then the highlight shifts, the diagram would essentially have to be animated, the same way you can only properly draw a 4-D object through animation, except time is already one of the axes on the diagram, so an animation of how this changes would involve some incomprehensible fifth dimension for how time changes over the fifth dimension's unit. Then again, maybe when you're talking about "changing" time, looking at "how time changes over the fifth dimension's unit" is in fact relevant, and with the agents not understanding exactly how they did it, perhaps there is something in that - or the hypothetical line essentially going down the dystopian branch then circling back on itself and through the other branch. Another option is perhaps that these universes all exist and Robin sees the timeline going through the statistically most likely outcomes at each split point, but that returns you to the previously mentioned problems with a tree of lots of equally valid universes.
 * As well as this, if there are numerous branches, why would the White Monolith just send them to one of those futures? And if it didn't, if it send them to all sorts of futures, you would have many versions of the agents all going back in time to the same stem 2017. There must be some sort of idea where there is a future in some regard, and where that can change.
 * With problems with the idea of infinite branches such as Robin's powers, the White Monolith just sending them to one future (if it didn't, you'd get many agents returning to the same 2017), it's possible that the idea of spinning out universes is somewhat separate from the "chang[ing]" of time in The End, being more of an explanation or the existence of the multiverse.
 * Deke Shaw: "But I am proof that you can move between them."
 * Deke saying he is proof you can move between these universes implies that the 2017-2091 jump and the 2091-2017 jump were not jumps between universes, otherwise he wouldn't be different to the others. They would just all be proof, and the agents in particular since they would have travelled first - to get there in the first place. So, when Deke says that he is proof you can move between them, he must be referring to the significance of being in a timeline where you'll never be born, as that's the only difference. This would suggest, therefore, that he believes the timeline they are currently in is already no longer headed for dystopia, for his future, but that that's fine because the dystopia still exists elsewhere in the multiverse tree. If they were now on a new branch from some divergence point c. late 2017/early 2018 since they got back, as it would appear he believes, then that doesn't change anything for Fitz and Simmons (and the others), who were born before the divergence point. It changes for him, because it means the timeline he's headed from is no longer the one they're in. He's proof, essentially, that if you "change time" then someone who theoretically shouldn't exist will not blink away, i.e. that you can safely shift to a world where you don't exist, because it's literally a different world.
 * The thing is, Deke wouldn't need proof you can move between them, by which he seems to mean, as established, proof you can survive outside one you're supposed to exist in. That's not really a problem if you've already established a multiverse existing, as there's no reason you wouldn't still exist if the multiverse existed. It's what he's establishing in the first place, "it could be the multiverse theory (in which case, I'm fine)", and then saying "and I'm proof that then you'd be fine". That's implicit in the first part, and he's not trying to prove any point about how someone would be okay switching timelines if it were a multiverse - I'm sure Fitz would agree, if it were a multiverse, someone would be okay switching timelines. What Fitz isn't sure about is whether there's a multiverse in the first place. So the only way this makes sense is if Deke's using his continued existence as proof of his point, and phrasing it poorly. Essentially saying, "Right now, there are infinite parallel universes instead of one timeline, and I'm proof of that, because I'm still around despite us changing things (having in a sense moved between them)! Plus of course that would show that you can survive in a timeline where you'll never exist, if you were wondering if you would or you wouldn't."
 * Leo Fitz: "Or, you are proof that we are in one timeline, in a loop an infinite, intractable, unchangeable loop."
 * Deke saying he is proof is inaccurate, even if you make the necessary assumptions about what he meant. Fitz points this out, he's only proof if they have already switched hypothetical timelines, but there is no reason to assume they have, so his continued existence could easily just be proof they're in one timeline and won't change things, so he will still be born. Fitz helpfully is pointing out the flaws in Deke's comments, which have been explored above. It would seem that his flawed comments essentially boil down to the fact that he's all too sure he's correct about the multiverse and making (poorly phrased) comments as if that's established as fact. Robin declares the change in events in The End, so Deke is wrong about himself already being proof of surviving outside of your timeline, since he's still on course for his future. It would seem again, that Deke's comments are more just included to seed an idea that will eventually pay off rather than to be fact here and now.
 * Jemma Simmons: "But, if we succeed in ridding the planet of gravitonium, then we break that loop and prevent the Earth's destruction."
 * Again, hoping to break the loop. The loop is a given.
 * Deke Shaw: "Which is great, because that definitely won't affect me at all. Look, it's not like I'm just gonna blink out of existence. I lived in one timeline, but now I live in this new one, and I think I'm gonna stay in the one with the sun and tacos and all that, because that's the multiverse, that's science."
 * This informed the above exploration of what Deke was seemingly trying to say about moving between universes, and how it's safe to shift into a world where you're not supposed to exist, because he believes (seemingly correctly) that you are literally shifting into a different world, not a new version of the world.
 * Deke referring to living in "one timeline" is a little murky, as what he says would imply he just means "section of time", saying he prefers 2018 to the 2091 he's from. But in the wider context of the conversation, and the fact that he says "I'm gonna stay in" this one, it would imply that he believes this one is not headed for dystopia, so the "timeline" thing does probably specifically refer to a timeline and not just a section in time. This would align with, and further support, the idea that he believes they have already shifted into a new branch (as discussed, he seemingly doesn't believe he time-travelled between universes, just has since shifted into a universe different to the one he's from). As discussed, Robin in The End would suggest he is slightly mistaken, but nonetheless has the right idea.
 * Leo Fitz: "Or you're a canary in a coal mine."
 * Deke Shaw: "I don't know what either of those things are."
 * Leo Fitz: "We won't know if we're successful at changing the future unless you blink out of existence."
 * Jemma Simmons: "Fitz..."
 * Leo Fitz: "Jemma agrees. She actually wrote a paper on the theory of -"
 * Jemma Simmons: "Nobody knows how it works."
 * Right now, before the actual destruction of Earth which would obviously show them whether they're successful, if Deke blinked out of existence then they would know that they have successfully changed the future, at least a little - that they've broken out of the time loop (and must be in a universe of just one singular timeline that gets rewritten). If Deke doesn't blink out of existence, as far as they know they might have already changed the future, but by the multiverse theory - so are in a new branch, but they would have no way of knowing. So only if Deke blinks away can they be sure they're successfully changing the future, for now.
 * Elena Rodriguez: "You need to listen. You saw her, me in the future. I spoke to her. She warned me of all of this."
 * Another comment about the future.
 * Elena calls the woman she saw "me", so it's a future her, not another version of her (if Elena is correct, but this nonetheless communicates the writers' intent).
 * Alphonso Mackenzie: "I don't want to hear it, and I don't want to know."
 * Elena Rodriguez: "She was trying to help us, Mack, to prevent this. To keep me from losing you. She said things that -"
 * Alphonso Mackenzie: "Yeah, and it's making you crazy. This whole future thing has got you all acting crazy. I don't wanna know. I'm just trying to fix the problems right in front of me, not get my mind twisted trying to figure out what comes next."
 * Elena Rodriguez: "We already saw what comes next!"
 * They have already seen what's about to happen, so what they saw had happened is what is about happen, it's the future, not another future (if Elena is correct, but this nonetheless communicates the writers' intent).
 * Alphonso Mackenzie: "So you're willing to do anything, no matter who it hurts?! We've been through too much [...] In the future we swore. We swore we wouldn't lose ourselves."
 * Another comment about the future.
 * Melinda May: "She's following a lead."
 * Phil Coulson: "A lead on what?"
 * Melinda May: A way to keep you alive.
 * Elena Rodriguez: "What?"
 * Phil Coulson: "I don't want that. My orders are very clear about that."
 * Melinda May: "If there's a chance we can save you, don't you think I'd take it?"
 * Phil Coulson: "Right now, we all need saving from our new overlords out there, and our most powerful team member's gone."
 * Elena Rodriguez: "No, no, no, no, no. I killed Ruby for nothing. It didn't matter, it's all happening, right now. Everything she told me."
 * Phil Coulson: ""She" who?"
 * Elena Rodriguez: "This, right here? This is how we lose. I could've warned myself about a lot of things. Ruby, Hale, these aliens... but instead, she told me - Instead, she told me, "Coulson is dying, and we need to let him." I'm sorry, sir. I hated keeping this. I owe you so much. You're my family."
 * Again, events are playing out exactly how 2091 Elena told 2017 Elena they would despite everything they try, further implying the time loop.
 * Melinda May: "No, you're wrong. Robin said Coulson puts the pieces back together. And you're saying that we should've just left him to freeze to death in the middle of nowhere."
 * Elena Rodriguez: "I have to listen, May [...] She was me. She's lived through this, through the loop..."
 * It was an older her, who has lived through what she's currently living, because current Elena will be that woman. It's not another Elena.
 * Another comment about the loop.
 * Elena Rodriguez: "... who knows how many times?"
 * Another comment that suggests that a time loop is somehow quantifiable, which it isn't, but presumably just a manner of speaking - a perspective of entering and going around and around - rather than an indication of something else, considering Elena is saying that her older self has lived through the loop over and over, that the one Elena is stuck in the loop - not that it's a different Elena each time in a chain.
 * Melinda May: "Exactly, you don't know. We haven't lost yet, and as far as we know, they can't get in here, - and until they do [...] you better believe we're gonna do everything possible to keep him alive."
 * The agents, as Elena is concerned about, are playing right into the exact future they are trying to avoid by trying to keep Coulson alive.
 * Alphonso Mackenzie: "Well, people in the future survive. There must be a way to stop them."
 * Another comment about the future.
 * Deke Shaw: "No, we didn't stop them."
 * "We", Deke is telling Mack about his experience in response to "the future", so he is from "the future" that Mack is referring to, the upcoming future, not some other future (if the characters are correct, but this nonetheless communicates the writers' intent).

Quote
[...] [...]
 * Deke Shaw: "It's like the universe keeps reminding me that I should never have come back from the future. [...] I lived in the Lighthouse my entire life, only to time travel into the past and still spend every single day of my life inside the freaking Lighthouse. So it's like, even without Kasius around, this place just has this leash that keeps pulling me back in."
 * Phil Coulson: "I know it sounds crazy, but the alien running Earth in the future was a Kasius."
 * Piper: "Prepare to be the first S.H.I.E.L.D. team in space."
 * Alphonso Mackenzie: "In this timeline, maybe."

Dissecting

 * Deke Shaw: "It's like the universe keeps reminding me that I should never have come back from the future."
 * Another comment about the future.
 * Deke Shaw: "I lived in the Lighthouse my entire life, only to time travel into the past and still spend every single day of my life inside the freaking Lighthouse. So it's like, even without Kasius around, this place just has this leash that keeps pulling me back in."
 * Another comment about purely "time travel" and the past, it would seem that Deke does not believe he switched universes in his time travel.
 * Phil Coulson: "I know it sounds crazy, but the alien running Earth in the future was a Kasius."
 * Another comment about the future.
 * Piper: "Prepare to be the first S.H.I.E.L.D. team in space."
 * Alphonso Mackenzie: "In this timeline, maybe."
 * This comment is confusing. Is it supposed to imply that there's another timeline where some other S.H.I.E.L.D. team got there before they did? Because there's nothing suggesting that at any point. I think it might just be Mack getting generally hopeful about multiple timelines.

Quote
[...] [...]
 * Jemma Simmons: "Should work. It's just..."
 * Leo Fitz: "What Yo-Yo said... danger."
 * Jemma Simmons: "Yeah."
 * Leo Fitz: "Well, I've been thinking about that, and her warning was that trying to save Coulson ends the world, right? But what if, what if, what if we don't just try? What happens if we actually succeed? Jemma, what if there's another way to frame this?"
 * Jemma Simmons: "Coulson wasn't there in the future. You're saying we break the loop not by allowing someone to die, but by making sure they live?"
 * Leo Fitz: "What if all we have to do is not fail?"
 * Jemma Simmons: "That's quite an audacious leap... especially from someone who once believed time cannot be changed."
 * Leo Fitz: "Maybe it's time to be audacious."
 * Phil Coulson: "That's the same writing that was in the Lighthouse in the future."
 * Glenn Talbot: "You drew me. You see me in your head, don't you? You ever see me tearing the Earth apart, bringing something up from the ground?"
 * Robin nods.

Dissecting

 * Jemma Simmons: "Should work. It's just..."
 * Leo Fitz: "What Yo-Yo said... danger."
 * Jemma Simmons: "Yeah."
 * Leo Fitz: "Well, I've been thinking about that, and her warning was that trying to save Coulson ends the world, right? But what if, what if, what if we don't just try? What happens if we actually succeed? Jemma, what if there's another way to frame this?"
 * Jemma Simmons: "Coulson wasn't there in the future. You're saying we break the loop not by allowing someone to die, but by making sure they live?"
 * The agents are still trying to find a way to "break the loop", the loop being a given. This one is just a more positive loophole way of breaking the loop, rather than a tragic one.
 * Leo Fitz: "What if all we have to do is not fail?"
 * Jemma Simmons: "That's quite an audacious leap... especially from someone who once believed time cannot be changed."
 * Leo Fitz: "Maybe it's time to be audacious."
 * The hope is that time can be "changed" in some way, not that they're in a different timeline. Their only optimistic outlook is that it is not true that "time cannot be changed".
 * Phil Coulson: "That's the same writing that was in the Lighthouse in the future."
 * Another comment about the future.
 * Glenn Talbot: "You drew me. You see me in your head, don't you? You ever see me tearing the Earth apart, bringing something up from the ground?"
 * Robin nods.
 * Again, Robin has seen the future of the timeline, that this will happen in the timeline, not in another timeline.

Quote
[...] [...] [...]
 * Deke Shaw: "I mean, besides, according to Fitz, if the world doesn't crack open and you break the time loop, I'll just blink out of existence anyway, so it's just one more vacancy, right?"
 * Leo Fitz: "Where's Mack?"
 * Melinda May: "Uh, in the ship. He went to find Polly."
 * Leo Fitz: "May... neither of them make it... Oh, no..."
 * Robin Hinton: "Something's different."
 * Phil Coulson: "And now he's frozen, out in deep space somewhere, no idea he's already solved it."
 * Jemma Simmons: "He'll be a little disoriented. But he'll be so happy to know that time is not fixed. It's a fluid, ever-changing, beautiful thing."

Dissecting

 * Deke Shaw: "I mean, besides, according to Fitz, if the world doesn't crack open and you break the time loop, I'll just blink out of existence anyway, so it's just one more vacancy, right?"
 * Fitz believes there is a singular timeline, so the only way they could break the time loop would be to rewrite time (which he doesn't think is possible, but if it is), thus causing Deke to blink out of existence. Fitz is later shown to be wrong - Deke stays around - but they did break out of the time loop, so this means they didn't rewrite time, Fitz was right about that not being possible, as also discussed in Avengers: Endgame.
 * Leo Fitz: "Where's Mack?"
 * Melinda May: "Uh, in the ship. He went to find Polly."
 * Leo Fitz: "May... neither of them make it... Oh, no..."
 * Neither of them "make it", not neither of them "made it". They are set to not make it, they are set to die, about to die, which they know because they learned from a point in the future that they previously died. Fitz doesn't know that the timeline is changed by this point (as Coulson has given Quake the serum), so from the perspective of assuming they are in the same position they were half an hour ago, then again, up to now, they have been in a time loop, what's about to happen is what happened when they were in the future (just it doesn't actually happen now, because the timeline is changed).
 * Robin Hinton: "Something's different."
 * Robin feels the shift at this point, implying she's been still seeing the dystopian future up until this point but the team have now gone off into a divergent timeline just now. It also, as discussed earlier, would mean that it's a timeline split at this point, and definitely not that this was always going to be the future of this universe.
 * As also discussed earlier, it would also seem that there is some sense of a main timeline or a future you are headed for, and that shifting, suggesting there are not just equally valid branches in a tree, specifically headed for the dystopian branch until this point, like this branch has just been split from the other timeline and wasn't necessarily, at least from some perspective, always due to split from it. Now, theoretically, all the timelines should already exist from a fourth-dimensional perspective, always due to split at the certain points, just only from the characters' perspective do they "go back" and create them. But perhaps there's something in that, that while Robin exists somewhat outside of a three-dimensional existence, she is still experiencing the characters' perspective of the branch timelines not yet being created, or again, there's some sort of fifth-dimensional thing involved where time changes over the fifth dimension's unit.
 * Phil Coulson: "And now he's frozen, out in deep space somewhere, no idea he's already solved it."
 * There are two versions of Fitz around post-May 2018, one 104 years old (not biologically) who has just died, and one who is 30 years old, still out there, frozen. Fitz lived through to 2091, then doubled back on himself so there are simultaneous Fitzes from December 2017. When the timeline splits in May 2018, there are two Fitzes, now separate, unbound. The 104-year-old dies, the 30-year-old is still frozen out in space and can be retrieved.
 * Imagine a piece of string next to a ruler, starting at point "1987.632cm". It continues through to "2091.999cm", where a portal is positioned. The string continues on, through the portal and out the other side, which is next to the string back at "2017.925cm", and the string continues again, side-by-side with its earlier self. Then, at "2018.412cm", a guillotine slices across, as the timeline splits off. The one piece of string is now two, one snipped about 30.8cm into its length, one snipped about 104.9cm into its length. Originally two points on the same piece of string, but now two loose ends, with their own futures, unbound. The 104.9cm one dies almost immediately, but the 30.8cm one is still out there to be found, essentially an old save file of Fitz from 74 years back in his life (but 73.6 of those spent frozen).
 * Another way to look at it is to look at the fork of the timeline. Follow it from the perspective of Fitz's life. His life goes as normal up to his 6 months imprisoned at Blue Raven Ridge. Fitz is then frozen. 6 months later, we hit the fork in the timeline. Going down the bad branch, he continues to be frozen. Going down the good branch, he comes out of freeze, and we get the Season 6 Fitz, who we will continue to be following in the show. The bad timeline, the frozen Fitz is still frozen until 2091. He goes back in time to December 2017. Over 5 months later, we hit the fork in the timeline again. Going down the bad branch, he ends up in the Lighthouse in the 2018-2022 events of The Last Day. Going down the good branch, he dies in an accident as the rubble falls on him. From Fitz's perspective, it's a two-pronged split, and then a further two-pronged split on one of those prongs. From the timeline's perspective, those splits are actually the same one split, with the prongs bending back on themselves. In either timeline, post-May 2018, there are always two Fitzes. In the bad timeline, there's 30-year-old frozen Fitz and 104-year-old Lighthouse Fitz. In the good timeline, there's 30-year-old soon unfrozen Fitz and 104-year-old dead Fitz.
 * Jemma Simmons: "He'll be a little disoriented. But he'll be so happy to know that time is not fixed. It's a fluid, ever-changing, beautiful thing."
 * The agents have found time is "not fixed", "ever-changing". They have in some capacity changed time, not just forged their individual universe, always an entirely separate universe from the dystopian one, a better future than the dystopian one. They have changed events and found time to be fluid, and the way the show presents is that no, you cannot rewrite events, but the next best thing is "spinning off" the universe the way Deke explained, however they did that exactly.

May 18, 2018: TVLine - Whedon, Tancharoen, and Bell Interview
https://tvline.com/2018/05/18/agents-of-shield-recap-season-5-finale-is-clark-gregg-leaving-iain-de-caestecker/

Quote

 * Matt Webb Mitovich: "The Fitz that Coulson hopes Simmons "finds" one day - that's the one who froze himself inside Enoch's ship in the other timeline?"
 * Maurissa Tancharoen: "Yes. He's on his way to save them."
 * Jed Whedon: "He went the long way, so [he and Enoch are] still traveling."

Dissecting

 * Matt Webb Mitovich: "The Fitz that Coulson hopes Simmons "finds" one day - that's the one who froze himself inside Enoch's ship in the other timeline?"
 * Maurissa Tancharoen: "Yes."
 * The question is poorly phrased, as regardless of theory, the Fitz they are currently hoping to find did not freeze himself in another timeline, he just froze himself 6 months ago. It can be assumed that the interviewer in fact means "the one who froze himself and in the other timeline was inside Enoch's ship for 74 years". So, with Maurissa Tancharoen's confirmation, it would also suggest a split in the timeline is the intention (with it being the same Fitz who froze himself, just not the same one at this point to the one who was still frozen in the other timeline) rather than always separate universes (which would mean it isn't at all the same Fitz).
 * Maurissa Tancharoen: "He's on his way to save them."
 * Jed Whedon: "He went the long way, so [he and Enoch are] still traveling."
 * He went the long way to save them, implying it's the same man who, in one timeline, arrived to save them after going the long way. And now, in this timeline, they can go and get him while he's still travelling. It's not an entirely different Fitz, just the same Fitz sent in a different direction from May 2018 on.

May 18, 2018: SYFY WIRE - Whedon, Tancharoen, and Bell Interview
https://www.syfy.com/syfywire/agents-of-shield-bosses-open-up-about-that-tragic-season-finale

Quote

 * Mike Avila: "But you did seem to leave the door open for a possible Fitz return, judging by what Jemma was talking with Coulson about in the aftermath."
 * Jed Whedon: "Right. Everybody got zapped to the future, and zapped back, plus Fitz. But Fitz traveled to the future the long way. He basically slept in cryo-freeze for 80 years. So there are technically two Fitzes in this timeline, so we just killed one of them."

Dissecting

 * Mike Avila: "But you did seem to leave the door open for a possible Fitz return, judging by what Jemma was talking with Coulson about in the aftermath."
 * Jed Whedon: "Right. Everybody got zapped to the future, and zapped back, plus Fitz.
 * Another comment about the future.
 * Jed Whedon: "But Fitz traveled to the future the long way. He basically slept in cryo-freeze for 80 years. So there are technically two Fitzes in this timeline, so we just killed one of them."
 * Describing how Fitz doubled back on himself, leaving two Fitzes around. The use of "this timeline" then seemingly is used to explain how they have two disconnected Fitzes around now they're in this timeline, rather than being the one Fitz at two different points in his life as before. Then the older one died.

November 27, 2018: Marvel's Avengers: Infinity War: The Cosmic Quest Volume Two: Aftermath
Page 96, page 169, page 170

Quote
[...] [...]
 * Felix Desta: "Do you think the Aether might be a Radical Quantum Selector?"
 * Darcy Lewis: "But the Aether isn't a stone... it's like a... blood cloud?"
 * Jane Foster: "Correct. And there's a reason for that. The Aether is the Reality Stone. While it was inside me, I experienced only a fraction of its abilities. Its shapeless form can possess a host body and give the body unlimited strength and unpredictable power. We knew that. But in its solid form, it can create illusions and twist our perceptions."
 * Felix Desta: "Then it is a Radical Quantum Selector! Hugh Everett III, the super-famous physicist, proposed that there are an infinite number of parallel universes out there. A lot of them would be similar to your own, while others could be totally different. Simply put, any reality you can think of? It exists. Sounds to me as if the Aether functions like a Radical Quantum Selector that allows its wielder to access these alternate realities and manifest them into our physical universe."
 * Jane Foster: "The green Time Stone allows its wielder to go backward or forward in time, changing whatever they see fit."

Dissecting

 * Felix Desta: "Do you think the Aether might be a Radical Quantum Selector?"
 * For context later.
 * Darcy Lewis: "But the Aether isn't a stone... it's like a... blood cloud?"
 * Jane Foster: "Correct. And there's a reason for that. The Aether is the Reality Stone. While it was inside me, I experienced only a fraction of its abilities. Its shapeless form can possess a host body and give the body unlimited strength and unpredictable power. We knew that. But in its solid form, it can create illusions and twist our perceptions."
 * Felix Desta: "Then it is a Radical Quantum Selector! Hugh Everett III, the super-famous physicist, proposed that there are an infinite number of parallel universes out there.
 * This is presented as if Desta has hit on the truth, implying that indeed, there are an infinite number of parallel universes. Parallel would imply never meeting - that there are entirely separate universes (not referring to ones that branch from each other).
 * Felix Desta: "A lot of them would be similar to your own, while others could be totally different. Simply put, any reality you can think of? It exists. Sounds to me as if the Aether functions like a Radical Quantum Selector that allows its wielder to access these alternate realities and manifest them into our physical universe."
 * An interesting description of how the Aether works, and "alternate realities" = "parallel universes".
 * Jane Foster: "The green Time Stone allows its wielder to go backward or forward in time, changing whatever they see fit."
 * Maybe it is possible to rewrite the singular timeline, but only through the use of the Time Stone, since Infinity Stones essentially have control over the universe and the ability to break physics.

Quote
[...] [...] [...] [...] [...]
 * Tony Stark: "Quantum fluctuation messes with the Planck scale, which then triggers the Deutsch proposition. Can we agree on that?"
 * James Rhodes: "If we can do this - you know, go back in time - why don't we just find baby Thanos, you know, and...?"
 * Rhodes mimes choking baby Thanos.
 * Smart Hulk: "First of all, that's horrible..."
 * James Rhodes: "It's Thanos!"
 * Smart Hulk: "... And secondly, time doesn't work that way. Changing the past doesn't change the future."
 * Scott Lang: "We go back, we get the stones before Thanos gets them... Thanos doesn't have the stones! Problem solved!"
 * Clint Barton: "Bingo."
 * Smart Hulk: "That's not how it works."
 * Clint Barton: "Well that's what I heard."
 * Smart Hulk: "Wait, by who? Who told you that?"
 * James Rhodes: "Star Trek, Terminator, Time Cop, Time After Time..."
 * Scott Lang: "Quantum Leap!"
 * James Rhodes: "... A Wrinkle in Time, Somewhere in Time..."
 * Scott Lang: "Hot Tub Time Machine!"
 * James Rhodes: "Hot Tub Time Machine! Bill & Ted's Excellent Adventure, basically any movie that deals with time travel..."
 * Scott Lang: "Die Hard!... No, that's not one."
 * James Rhodes: "... This is known."
 * Smart Hulk: "I don't know why everyone believes that but that isn't true. Think about it: if you travel to the past, that past becomes your future, and your former present becomes the past which can't now be changed by your new future."
 * Nebula: "Exactly."
 * Scott Lang: "... So Back to the Future ' s a bunch of bulls**t?"
 * Ancient One: "If I give up the Time Stone to help your reality I'm dooming my own."
 * Bruce Banner: "With all due respect, alright, I - I'm not sure the science really supports that."
 * The Ancient One conjures a magic timeline, with the six Infinity Stones circling it.
 * Ancient One: "The Infinity Stones create what you experience as the flow of time. Remove one of the stones..."
 * The Ancient One swipes the Time Stone from the line, and a black line splits from the magic timeline.
 * Ancient One: "... and that flow splits. Now this may benefit your reality, but my new one, not so much. In this new branch of reality, without our chief weapon against the forces of darkness, our world would be overrun. Millions will suffer. So tell me doctor, can your science prevent all that?"
 * Bruce Banner: "No... but we can erase it. Because once we're done with the stones, we can return each one to its own timeline at the moment it was taken, so..."
 * Bruce takes the Time Stone the Ancient One swiped aside.
 * Bruce Banner: "... chronologically, in that reality..."
 * Bruce replaces the Time Stone, and the black line disappears.
 * Bruce Banner: "... it never left."
 * Steve takes four vials of Pym Particles from Hank Pym's office.
 * Smart Hulk: "And remember, you have to return the stones to the exact moment you got 'em or you're gonna open up a bunch of nasty alternative realities."
 * Steve Rogers: "Don't worry Bruce... clip all the branches."
 * Steve Rogers: "Well, after I put the stones back..."

Dissecting

 * Tony Stark: "Quantum fluctuation messes with the Planck scale, which then triggers the Deutsch proposition. Can we agree on that?"
 * The dissection of this quote can be found under July 20, 2019, the Time Travel in the Quantum Realm San Diego Comic-Con 2019 panel.
 * James Rhodes: "If we can do this - you know, go back in time - why don't we just find baby Thanos, you know, and...?"
 * Rhodes mimes choking baby Thanos.
 * Smart Hulk: "First of all, that's horrible..."
 * James Rhodes: "It's Thanos!"
 * Smart Hulk: "... And secondly, time doesn't work that way. Changing the past doesn't change the future."
 * You can't just rewrite time in the way many films do time travel.
 * It's interesting that he says "changing the past", not "visiting the past". It implies that time can be changed if you go back in time, not just visited in a causal loop/bootstrap paradox. However, when you make a change it doesn't impact this timeline, for whatever reason.
 * Also interestingly about the fact he says "changing the past" and not "visiting the past", Bruce is already confident you can change the past. This could be because he already knows that the Infinity Stones are involved in meddling with time and so they'll be capable of changing things, but the way he and Nebula agree and the scene is done feels more like, "These guys are more scientifically knowledgeable so they know about changing the past." This would imply that you are capable of changing time anyway.
 * Scott Lang: "We go back, we get the stones before Thanos gets them... Thanos doesn't have the stones! Problem solved!"
 * Clint Barton: "Bingo."
 * Smart Hulk: "That's not how it works."
 * Clint Barton: "Well that's what I heard."
 * Smart Hulk: "Wait, by who? Who told you that?"
 * James Rhodes: "Star Trek, Terminator, Time Cop, Time After Time..."
 * Scott Lang: "Quantum Leap!"
 * James Rhodes: "... A Wrinkle in Time, Somewhere in Time..."
 * Scott Lang: "Hot Tub Time Machine!"
 * James Rhodes: "Hot Tub Time Machine! Bill & Ted's Excellent Adventure, basically any movie that deals with time travel..."
 * Scott Lang: "Die Hard!... No, that's not one."
 * James Rhodes: "... This is known."
 * Smart Hulk: "I don't know why everyone believes that but that isn't true."
 * This is all them discussing again the idea that you can't just rewrite time in the way science fiction films often suggest.
 * Smart Hulk: "Think about it: if you travel to the past, that past becomes your future..."
 * When you travel to 2012, that chunk of the past you are now living in is now in your present and future.
 * Smart Hulk: "... and your former present becomes the past."
 * 2023 is now in your personal past.
 * Smart Hulk: "Which can't now be changed by your new future."
 * Just by being in 2012, nothing you do can change your personal past of your 2023.'
 * "New future" is interesting: As in it's literally a new future that has been changed, or just this is your "new future" because time is realigned from your perspective in the way Smart Hulk just laid out about how the past becomes your future? Either way though doesn't particularly matter because if it's the latter, it's just a continuation of what he's been saying about the adjustment of 2023 now being in your past etc., and if it's the former then he's saying that when you have changed time, you are now in a new timeline - something that is not disputed. It's what can allow you to change time/cause a new timeline that's in question.
 * The only problem with not clearly knowing which way Hulk means by "new future" is that, if he is referring to a literal new future of an alternate timeline, then, while the conversation is still predicated on changing time nonetheless, he does in his explanation say "If you travel to the past", as if that were what would happen regardless, not just in the scenario of someone changing time. In that case, Hulk could be seen to be saying that if you travel to the past, you create an alternate timeline. But there's several assumptions involved there and ultimately, it's not possible to know what Hulk means - he seems to just be talking about a shift in perspective, anyway. This scene appears to more just be about establishing the "You can't rewrite time" rule than the rules of creating alternate realities.
 * Indeed, Banner's comments about how the main timeline can't be changed by your new future apply in either sense. "Because you are just in the timeline, in a time loop" or "Because you aren't in that timeline anymore".
 * Nebula: "Exactly."
 * Scott Lang: "... So Back to the Future ' s a bunch of bulls**t?"
 * Just another affirmation of the classic sci-fi rules of rewriting time being wrong.
 * Ancient One: "If I give up the Time Stone to help your reality I'm dooming my own."
 * Either they are already in different realities or she's saying that it would create a different reality if she gave up the Time Stone, and thus doom her reality that he's leaving behind.
 * Bruce Banner: "With all due respect, alright, I - I'm not sure the science really supports that."
 * The Ancient One conjures a magic timeline, with the six Infinity Stones circling it.
 * Ancient One: "The Infinity Stones create what you experience as the flow of time. Remove one of the stones..."
 * The Ancient One swipes the Time Stone from the line, and a black line splits from the magic timeline.
 * Ancient One: "... and that flow splits."
 * This is fairly self-explanatory. Remove a stone from its timeline and the timeline splits in two. You have a branch of two timelines.
 * Specifically said that the flow of time "splits", in two as shown.
 * It is not stated that this is the only way the flow can split, though it is implied considering alternate timelines are crucial to the film and this is the only time their creation is mentioned.
 * If this is not the only way the flow can split, then it is possible that they are already in a branch timeline, and are then causing that timeline to split - so a branch on a branch, potentially meaning that the erasing brought up later is just erasing bad branches on the already-existing branches, and not just erasing the whole branch from the main timeline.
 * Infinity Stones being the only way in this film to create new timelines would make scientific sense, since travelling through time alone should only keep you in a causal loop - if you travel back to 2012, then in 2012, you were there. The Infinity Stones, a wholly fictional construct with the power to manipulate the flow of time as the Ancient One explains, would make sense as a way to break this.
 * The Ancient One doesn't actually refer to time travel, so why would removing an Infinity Stone specifically be the only "time travel rules"? Well, if Infinity Stones are the only things causing timeline splits, that doesn't mean they're the only time travel rules. The rules would still be there, just be "you can't really change time", and then the Infinity Stones are just a rule in general which happens to, in this instance, pertain to time travel since it is the method through which the Infinity Stones would be removed from the timeline.
 * Ancient One: "Now this may benefit your reality, but my new one, not so much."
 * The orange line is Bruce's reality, the main reality as we call it. But in removing a stone, he leaves behind that dark "new" reality with the Ancient One in it, and it causes her problems.
 * If this were just a split on what is already a branch, then that would mean Bruce's reality is not the orange line, it's neither line. Granted she doesn't say the orange line is Bruce's, but it's implied. More important is her saying "my new one", implying that she, as she is speaking to Bruce, will be left behind in a dark timeline, and not that she will be split into two timelines, with one version in the okay timeline and just one not. This implies that removing the stone will not cause a further branch than the branch already happening, she will be stuck in the bad timeline, so since the removal of the Stone does split the timeline, that branch being something already happening would mean the split should be because of the stone, and not a split from arrival and a further split from the stone, as there's only one split.
 * Realities = branches in the flow of time.
 * Ancient One: "In this new branch of reality, without our chief weapon against the forces of darkness, our world would be overrun. Millions will suffer."
 * The timeline branch is a branch of reality. So perhaps "reality" is the totality of branches - the tree of timelines - but also each branch of the timeline is a mini reality. Or it's just her way of saying branch reality.
 * Ancient One: "So tell me doctor, can your science prevent all that?"
 * Bruce Banner: "No... but we can erase it."
 * They cannot prevent the suffering that would happen by removing the stone. However, they can erase the suffering from existence.
 * Bruce Banner: "Because once we're done with the stones, we can return each one to its own timeline at the moment it was taken."
 * So each stone would be returned to each branch timeline. At the moment it was taken - presumably means the exact moment the Avengers disappear to return to 2023 with the stones in hand.
 * There is no precedent for being able to navigate the alternate timelines in the film, like travelling back to 2012 and then forward down the offshoot timeline to where the stone left, so it might be the case that the exact moment they got there would be some sort of volatile point where the branch timelines start to break away due to the Infinity Stones being removed from that bubble, and they're putting them back to eliminate the bubble from forming into a full timeline.
 * If it is not as simple as stopping a volatile point, you have to make assumptions about being able to navigate the branch timelines.
 * If Steve does literally have to return the stones within the locations, we should note that Bruce doesn't say the exact place. Steve presumably could, for example in 2014, show up nearby on Morag at the exact moment Rhodey leaves.
 * Bruce Banner: "So..."
 * Bruce takes the Time Stone the Ancient One swiped aside.
 * Bruce Banner: "... chronologically, in that reality..."
 * Again using "reality" to mean timeline. I believe that reality as a whole is the tree of timelines, but each branch timeline is a reality.
 * Bruce replaces the Time Stone, and the black line disappears.
 * Bruce Banner: "... it never left."
 * The stone is always present in the timeline.
 * It would seem from the return journeys that it's okay to have two of the same stone present at once since Steve takes them all and drops them off one-by-one instead of returning for each.
 * The black line disappearing is interesting. They are "eras[ing]" the suffering from existence rather than preventing it. Returning the stones to their time but the timelines continuing would mean they are merely preventing it. The black line dissipates, it disappears, it's erased. Returning the stones has to in some way erase some dark splinter timeline.
 * It would seem that the timeline became volatile as they removed the stones, but in returning them there was never a moment where the stones were gone, so the timeline doesn't split. The leaving almost creates a dark splinter timeline, but it's erased by the returning of the stones.
 * A way of fudging this comment, if you want to accept that the branches continue, is to take it that they are still in fact preventing the suffering, but in a different manner. That the Ancient One is asking, "What, are you going to fly around to all these places and stop all the suffering that would be caused?" ("prevent" suffering practically), and Bruce is responding, "No, we'll just stop the suffering from ever happening" ("erase" the suffering from ever having to happen, which is still preventing but can, in a sense, be seen as erasing). But this still does not align with the black splinter line dissipating.
 * Bruce saying "that reality" refers to the Ancient One talking about "this new branch of reality". So when he says in that reality it never left, accompanied with the dark line disappearing, he is seemingly essentially saying, "In that reality it never left, so that reality actually in the end doesn't ever exist." The dialogue on its own can be taken to mean, "In that new reality, it at least still always has an Infinity Stone," still meaning there's a new reality, just it's not Infinity Stone-less - but in conjunction with the timeline diagram, it's got to be erased, otherwise it would just be the dark line becoming orange as well.
 * If it's only removing Infinity Stones in this film that makes the timeline split, how do you account for the fact that time is nonetheless changed by their actions before you remove an Infinity Stone? After all, the events in 2012 and 2014 are simply incompatible with the original timeline. It's not like until the stone is removed then they are stuck in a causal loop and time is the same as it always was, because certain things happen that cannot have happened, and what would've happened in the main timeline at the time the stones are removed, minutes later, in the new one? The 2023 versions of the characters who had been coexisting in the timeline just... disappeared? The first answer might be to say that it's not removing the stones from the time stream that makes the difference, but removing them from their intended place in space-time. But then you still have the problem of the Power Stone, which hasn't been moved yet when Rhodey knocks Quill out, and also still the question of what happened to the 2023 versions of the characters in the original timeline when the stones get moved, having been there for a few minutes. The other option is to essentially look at time somewhat in the scientific way where it's all laid out already and we're just moving through it. Since Infinity Stones get removed, it makes beach one a branch timeline, and therefore was always going to be a branch timeline from the moment they arrived.
 * The removal of an Infinity Stone theoretically should indeed be somehow solidifying everything since arrival as a splinter timeline. The removal of an Infinity Stone definitely, explicitly splits the flow of time, so if the removal of an Infinity Stone were to only cause time to split at the point it were removed, you would end up with the Avengers being present in that time, and then a split when they go back leaving a timeline without an Infinity Stone, and a timeline still with it. Except, how? The Avengers going back is what removes the stone from the timeline, so you would have to have the split occur, say, the moment they hit the button to return, so in one version of events they disappear and in one they do not. So, why? Does it just not work? Why wouldn't it? And in that case, you also end up with versions of the Avengers abandoned in time (unless you end up with the timelines erased, but if timelines are indeed erased it is said to be the ones without Infinity Stones, so if there are also branch timelines with Infinity Stones, you wouldn't be erasing this) which is bizarre. You could question whether perhaps, because it's not actually said that it would be one timeline with stones and one without, maybe both timelines are missing a stone. That solves your stranded Avengers problem, except it is shown that removing an Infinity Stone creates one dark branch of reality specifically dark because it's missing an Infinity Stone, not that it poisons both timelines. Overall, this suggests that some sort of system where it would make everything since arrival an alternate timeline, thus meaning you were always in an alternate timeline since you arrived. Why the Infinity Stones would in some sense "choose" to do that is unclear, but if they didn't, it wouldn't fit with what the film presents, so this is just a possible necessary assumption. Tying in with Marvel's Agents of S.H.I.E.L.D., it would make sense that, in either case, if you are a time-traveller you somehow make the timeline after you arrive back in time volatile, less stable (after all, Marvel's Agents of S.H.I.E.L.D.: Season 6 shows that, for example, Deke Shaw is in a sense detectable as someone out of their natural time/universe, there is some sort of trace), and can take advantage of that or by removing an Infinity Stone cause that to be a split. The timeline, say, is like a piece of wood that has become weaker from the moment of arriving back, and if then a big nail is suddenly hammered in further down (Infinity Stone is removed), the wood will split, stretching back through the weaker wood to the point where it stopped being strong (back to arrival). This is not particularly making some sort of excuse for this version of removing an Infinity Stone somehow being different, since there does not seem to be any other way of removing an Infinity Stone anyway other than moving it to a different universe, so it would just be the rules of removing an Infinity Stone.
 * As explained, there is a problem with the idea that removing an Infinity Stone would somehow split the timeline only from the point in time when it is removed. As well as suggesting some sort of making everything since arrival into an alternate timeline, this also goes against the idea of the timeline already splitting on arrival, since it would require the timeline to somehow split again on that branch, which does not seem plausible.
 * Steve takes four vials of Pym Particles from Hank Pym's office.
 * Steve is shown to take four vials of Pym Particles from Hank Pym's office (and possibly more off-screen), despite only needing two: one for him, one for Tony. There is a possibility that this is foreshadowing, shown because it is Steve taking a pair of vials to later allow himself to jump to the 1940s to live with Peggy, then back to 2023, having made his decision by this point. With the nature of film-making to often seed things like this as a subtle detail to pick up on, it is very possible. In-universe, Steve may have many other reasons for taking more than two vials of Pym Particles. He could be taking several to simply have spares just in case something goes wrong or has gone wrong for any of the others on their missions, because it doesn't make a difference and could be vital. He could be taking several to then allow them to get back and return each of the Infinity Stones, in case they don't manage to bring everyone - including Hank Pym - back. He could be taking two extras in case he needs one to get back from living with Peggy, not sure if he needs it or not. And the thing is, if it were him taking two extras for his intention to live with Peggy, it isn't particularly necessary. Their intention is to bring Hank back, and then they will have an infinite supply of Pym Particles. If they don't successfully bring everyone back, it is hard to believe that Steve would still retire and go off to live with Peggy in the past. So if he's only going to retire if they bring Hank back, then he needn't get Pym Particles there and then - again, it would have to be a "just in case, because why not?", like any other reason he could take more than two, unless Steve did plan to retire even if they fail, or he didn't want to ask for extra back in 2023 so people didn't know about his intention. The nature of film-making would slightly lean it toward the idea of Steve being in an alternate timeline with Peggy, but there are many reasons why it could be anything.
 * If following the theory that this is for Steve to go and live with Peggy and then get back, then it would imply that - if Steve knows what he's doing - he would get back with a Pym Particle, i.e. through the Quantum Realm, rather than any other medium.
 * Smart Hulk: "And remember, you have to return the stones to the exact moment you got 'em or you're gonna open up a bunch of nasty alternative realities."
 * If Steve doesn't get them back to exactly where they were, it leaves a moment where a timeline is Infinity Stone-less and timelines will start branching. Hence a moment in the timeline without all six different Infinity Stones leads to a split in the timeline/reality.
 * This quote begs the question: Would he be opening up specifically nasty realities (as in when he puts back the stones he's making sure that that there are specifically no nasty alternative realities, not that there are no alternative realities whatsoever), or just opening up realities, which could be nasty (he's making sure no realities which are nasty are left behind, just okay ones)?
 * This should mean Steve does not create realities by travelling back. If every time you travel back you create a new timeline from where you arrive, then Steve would create a branch on every branch he's visiting, meaning he's just creating a new okay timeline but nonetheless leaving behind a nasty alternative reality.
 * Steve Rogers: "Don't worry Bruce... clip all the branches."
 * So he's getting rid of branches. He's clipping them. He's not just rectifying them. This matches the fact that Bruce specifically says that you cannot prevent the suffering, but can "erase" it.
 * The fact that he's clipping all the branches would imply that he's erasing all the branches which could otherwise potentially have been nasty, not just erasing the nasty branches and leaving some others. This was part of Bruce's promise to the Ancient One.
 * If the timelines are not all erased, there is a problem with the possibility that the Avengers have just started a disastrous, innumerable chain of timelines. After all, at least the 1970 and 2013 timelines almost certainly have Thanos' Snap in their future - the changes will not have affected that. The insignificant changes they caused would mean an eventuality where, almost certainly, they hit 2023 and have the exact same idea for the Time Heist. They then go back and would cause splinter timelines themselves from 1970, 2012, and 2013, some of those from which you would again end up with a Time Heist, causing further splinters off those. Granted, the 2013 timeline's 2023 Avengers who go back to 2013 would find things slightly different, with main timeline Thor present in that 2013, but the ones going to 1970 would still cause a normal splinter timeline, with that 1970 still different. You could cause a countless number of disastrous chains, and if those chains do have an end, many of them would only be ending because the Avengers don't have the Time Heist idea in the same way (after all, they had a one in fourteen million chance in the main timeline, one significant change and there's a good chance they don't succeed), so could also have doomed innumerable timelines to tragedy in saving their own. They would have started an uncontrollable catastrophic mess, especially hard to believe with Bruce's insistence that they're going to put everything right and keep it under control.
 * If Steve makes sure there is never a point where the stones aren't a complete set, then technically, should there therefore never be any alternate timelines created at all, when there must be for events to play out differently? If they are entirely prevented from coming into existence, then they never existed to visit. An explanation for this could tie into Christopher Markus' unclear comment about being able to do whatever you like without fear for the main timeline changing, and the Clifford V. Johnson comment about stitching the universe differently. Their interference is not an actual alternate timeline, more of an aside like the Dormammu loop, but the problem is that then they remove an Infinity Stone which causes a proper split in the timeline. However, this does not particularly fit with the Steve explanation. More likely, it can be taken that the timelines just collapse at the point the stones are returned (the same moment they're taken). The removal of the Infinity Stones still in some way had an effect, despite the returning at the exact same moment - it allowed for branch timelines. But the branch timelines then collapse at the moment of return.
 * And "all the branches" - every branch has to go. This would imply that no branches are left, and therefore Clint's trip and Steve's trip did not open up branches, as those ones can't be closed, nor did just jumping in time cause branches in 1970, 2012, 2013, or 2014 - only the removal of the Infinity Stones, which can be erased.
 * Steve Rogers: "Well, after I put the stones back..."
 * Steve did manage to put the Infinity Stones back, so the method works.

April 29, 2019: The New York Times - Markus and McFeely Interview
https://www.nytimes.com/2019/04/29/movies/avengers-endgame-questions-and-answers.html

Quote
[...]
 * Dave Itzkoff: "It's crucial to your film that in your formulation of time travel, changes to the past don't alter our present. How did you decide this?"
 * Christopher Markus: "We looked at a lot of time-travel stories and went, it doesn't work that way."
 * Stephen McFeely: "It was by necessity. If you have six MacGuffins and every time you go back it changes something, you've got Biff's casino, exponentially. So we just couldn't do that. We had physicists come in - more than one - who said, basically, "Back to the Future is [wrong].""
 * Christopher Markus: "Basically said what the Hulk says in that scene, which is, if you go to the past, then the present becomes your past and the past becomes your future. So there's absolutely no reason it would change."
 * Dave Itzkoff: "Thor recovers his hammer, Mjolnir, by taking it from an earlier timeline. So that raises the question - "
 * Stephen McFeely: "Does that screw that other Thor?"
 * Christopher Markus: "Is he killed by Dark Elves?"
 * Stephen McFeely: "I think we're leaning on, when you just take a baseball mitt, you didn't ruin that kid's life. When you took Mjolnir, we accept that that movie happened. Because time is irrefutable."
 * Christopher Markus: "You can make any number of what ifs. The Dark Elves would have arrived, intending to get the Aether. It's what they came for and it was no longer there."
 * Stephen McFeely: "So they build a paradise together."
 * Christopher Markus: "They all got married."
 * Laughter.

Dissecting

 * Dave Itzkoff: "It's crucial to your film that in your formulation of time travel, changes to the past don't alter our present. How did you decide this?"
 * Christopher Markus: "We looked at a lot of time-travel stories and went, it doesn't work that way."
 * Stephen McFeely: "It was by necessity. If you have six MacGuffins and every time you go back it changes something, you've got Biff's casino, exponentially. So we just couldn't do that."
 * So not every time you go back does it change something. However, while "something" could be referring to changing a piece of time, it is more likely in context that McFeely is referring to rewriting the main timeline, and how it's too difficult to have every tweak rewrite things in the main timeline.
 * Stephen McFeely: "We had physicists come in - more than one - who said, basically, "Back to the Future is [wrong].""
 * This, again, seems to be specifically about the idea of, "In going back, you would rewrite the one timeline."
 * Christopher Markus: "Basically said what the Hulk says in that scene, which is, if you go to the past, then the present becomes your past and the past becomes your future. So there's absolutely no reason it would change."
 * If you go to the past, say 2012, then 2023 is now in your personal past while 2012-2023 is now your future. And then he says that there's absolutely no reason why that would change because your past is now ahead of you to be lived through, seemingly describing a causal loop. Markus would therefore be suggesting that Hulk is not referring to alternate timelines when he says this, just that you can't directly change the past.
 * Dave Itzkoff: "Thor recovers his hammer, Mjolnir, by taking it from an earlier timeline. So that raises the question - "
 * Stephen McFeely: "Does that screw that other Thor?"
 * Christopher Markus: "Is he killed by Dark Elves?"
 * McFeely saying this implies there's precedent for there being some other Thor without Mjolnir now. But Steve returned Mjolnir with the Reality Stone, said to erase the bad timeline without the Reality Stone (and Mjolnir), regardless of whether that's the only branch in 2013 or whether it's a branch on a branch - there should be no Mjolnir-less timeline. This comment would suggest that the timelines created still exist, even the stone-less ones regardless of whether they are the only branch timelines or branches on branches. This fits with a major problem with the "every jump in time creates a branch" point of view, because in that case Steve would only create a new, nicer timeline at the point of each return and not do anything to rectify the timeline missing an Infinity Stone. But that idea flies in the fact of the film. Ultimately, it's important to note that they are joking through this part of the interview.
 * Stephen McFeely: "I think we're leaning on, when you just take a baseball mitt, you didn't ruin that kid's life. When you took Mjolnir, we accept that that movie happened. Because time is irrefutable."
 * What he says about the baseball mitt, referring to Clint's test run, would imply that Clint did make a change to his child's life. However, that doesn't necessarily mean it is an alternate timeline being created, as if Clint always took that baseball mitt c. 2018, then he took that glove, he still acted even if it didn't create an alternate timeline. McFeely is just saying that that action did not ruin the child's life, with no particular regard to whether it's in the same timeline or a different one. However, he then likens the Mjolnir comment to this, and with the Mjolnir discussion they are talking about an alternate timeline, perhaps implying the baseball mitt is actually an alternate timeline, but also what they are saying about Mjolnir does not particularly make sense, and is all part of a joke response.
 * The second part resembles a discussion from X-Men: Days of Future Past: "Now there's a theory in quantum physics that time is immutable. It's like a river, you can throw a pebble into it, create a ripple, but the current always corrects itself. No matter what you do, the river just keeps flowing in the same direction." McFeely seems to be implying that this timeline would play out similarly without Mjolnir, despite the brief difference in events.
 * A different way of interpreting what he says is he is just talking about that Thor: The Dark World still happened in the main timeline as it was because time cannot be changed, thus also meaning that in likening the baseball mitt to it, there isn't any sort of alternate timeline implication. But that doesn't really fit with the discussion being about removing Mjolnir.
 * Christopher Markus: "You can make any number of what ifs. The Dark Elves would have arrived, intending to get the Aether. It's what they came for and it was no longer there."
 * This again implies that the Reality Stone-less timeline continues to exist, despite what the film says - unless this is interpreted as them discussing what might have happened if that timeline had continued to exist.
 * Stephen McFeely: "So they build a paradise together."
 * Christopher Markus: "They all got married."
 * Laughter.
 * Again, worth noting that they're joking throughout this Thor: The Dark World part, so it's perhaps not worth putting too much weight into.

April 30, 2019: Entertainment Weekly - Russos Interview
https://ew.com/movies/2019/04/30/avengers-endgame-russo-brothers-captain-america/

Quote

 * Joe Russo: "If Cap were to go back into the past and live there, he would create a branched reality. The question then becomes, how is he back in this reality to give the shield away?"
 * The brothers smile.
 * Joe Russo: "Interesting question, right? Maybe there's a story there. There's a lot of layers built into this movie and we spent three years thinking through it, so it's fun to talk about it and hopefully fill in holes for people so they understand what we're thinking."

Dissecting

 * Joe Russo: "If Cap were to go back into the past and live there, he would create a branched reality."
 * Just by going back and living there, he creates a branch.
 * Joe Russo: "The question then becomes, how is he back in this reality to give the shield away?"
 * The brothers smile.
 * Joe Russo: "Interesting question, right? Maybe there's a story there. There's a lot of layers built into this movie and we spent three years thinking through it, so it's fun to talk about it and hopefully fill in holes for people so they understand what we're thinking."
 * One of the big problems with the Russos' explanation is that Steve seemingly should not be able to get back to the main timeline without coming through the Quantum Tunnel, as there is nothing in the film setting up a way he could come back without doing that. In the film, as is evidenced particularly by Hawkeye's test run, the Avengers are yanked back to their timeline's 2023. After the Hawkeye test run, they can hit a button to choose to do it themselves rather than just being pulled back after a certain amount of time. But still, they seem to essentially hit a "return" button and get yanked back like they are on a wire and harness, returning to a few seconds after they left, as programmed. So Steve should, if he's coming from an alternate timeline, just come back out of the Quantum Tunnel 5 seconds after he left, with no precedent for otherwise programming your suit to not yank back but still somehow get back to your timeline, just at a different time to when you left. And even if that were possible, why would Steve choose to do that, when he can just come out of the Quantum Tunnel as normal? After all, if he's in an alternate timeline, then he's coming back the exact same way that the Avengers did from Time Heist missions - travelling to a time, getting into an alternate timeline, then returning to the point a few seconds after you left. Why would he over-complicate things to come out at a different time or in a different way? And the Russos do seem to acknowledge that here, that there is a hole in their explanation. However, although it is unsatisfying, they are addressing the point and saying that an explanation exists, but it's intentionally mysterious. So this somewhat nullifies the hole, because it's somewhat as if they've explained it.
 * The theory that he just used the space-time GPS to come out by the bench does not make sense, as all that device seems to do is shift you through time and space. It very much seems that there is no setting for which timeline you want it to jump to - that you shouldn't just be able to make jump laterally across timelines with it to another point in another timeline, you would have to be yanked back. Another problem with this is that, going by the Russo explanation, a jump with the GPS seems to create an alternate timeline, so Steve could not really get back to the main timeline with it as it would just cause a branch when he arrives - unless it is to be taken that all of the rest of the MCU is following that branch.

April 30, 2019: QQ - Russos Interview
https://ent.qq.com/a/20190429/007983.htm Translation: https://www.reddit.com/r/marvelstudios/comments/bj0it4/joe_russos_qa_about_the_plot_of_avengers_endgame/

Quote
[...] [...]
 * Xiang Rong: "Peggy Carter was probably already married and in her mid-40s in 1970, in that case what year was it that Captain America went back to dance with her?"
 * Joe Russo: "We can't answer it for now, this is a story that happened in an alternate reality. Maybe it will be revealed in the future."
 * Xiang Rong: "Did Captain America's action at the end affect the timeline? Does that mean there was a time where two Captain Americas existed in a same universe?"
 * Joe Russo: "To me, Captain America's action in the end wasn't the fact he wanted to change anything, it's more like me has made a choice. He chose to go back to past and lived with the one he loved for the rest of his life. The time travel in this movie created an alternate reality. He lived a completely different life in that world. We don't know how exactly his life turned out, but I'd like to believe he still helped many others when they were needed in that world. Yes, there were two Captain Americas in that reality, it's just like what Hulk said, what happened in the past has already happened. If you go back to past, you simply created a new reality. The characters in this movie created new timeline when they went back to the past, but it had no effect to the prime universe. What happened in the past 22 movies was still canon."
 * Xiang Rong: "How would Cap react when he encounters Red Skull when he returned the stone?"
 * Joe Russo: "Red Skull would probably put the Soul Stone back to its location, and wait for the next unfortunate stone-seeker to make a sacrifice. Cap and Red Skull probably won't fight. It's because it's his mission to return the stone to its original place. The Red Skull is also no longer the same Red Skull from The First Avenger. He is more like a ghost, you could almost say he's a completely different entity now. He only exists to guard the stone, his past conscious may or may not exist anymore.
 * Xiang Rong: "Endgame ' s plot, is it a parallel universe or a closed time loop?"
 * Joe Russo: "Nope, not a time loop. Both Ancient One and Hulk were right. You can't change the future by simply going back to past. But it's possible to create a different alternate future. It's not butterfly effect. Every decision you made in the past could potentially create a new timeline. For example, the old Cap at the end movie, he lived his married life in a different universe from the main one. He had to make another jump back to the main universe at the end to give the shield to Sam."

Dissecting

 * Xiang Rong: "Peggy Carter was probably already married and in her mid-40s in 1970, in that case what year was it that Captain America went back to dance with her?"
 * Joe Russo: "We can't answer it for now, this is a story that happened in an alternate reality. Maybe it will be revealed in the future."
 * Again, Joe Russo says that Steve's time with Peggy was an alternate reality.
 * Xiang Rong: "Did Captain America's action at the end affect the timeline? Does that mean there was a time where two Captain Americas existed in a same universe?"
 * Joe Russo: "To me, Captain America's action in the end wasn't the fact he wanted to change anything, it's more like me has made a choice. He chose to go back to past and lived with the one he loved for the rest of his life."
 * I will address the thing about Captain America not interfering with the past later, but this also contributes to that, Joe Russo saying he didn't want to change anything.
 * Joe Russo: "The time travel in this movie created an alternate reality."
 * Yes, this sounds like Joe Russo saying that all the time travel points are in one alternate reality, which doesn't make sense, but I wouldn't over-analyse this - it'll be the translation and he just means, "The time travel in this movie created alternate realities."
 * Joe Russo: "He lived a completely different life in that world. We don't know how exactly his life turned out, but I'd like to believe he still helped many others when they were needed in that world. Yes, there were two Captain Americas in that reality..."
 * Joe Russo describes how this is an alternate reality again.
 * He adds a different "world" to the equivalent words with "timeline" and "reality". This implies that splitting the timeline does indeed contribute to the MCU ' s multiverse, that it's not in some sense the branch timelines of one universe but that the branches are universes themselves.
 * Joe Russo: "... it's just like what Hulk said, what happened in the past has already happened. If you go back to past, you simply created a new reality."
 * Here, Joe Russo reiterates that you cannot rewrite time.
 * Joe says that if you go back to the past, you simply create a new reality, which would mean that every jump into the past creates a split in the timeline, though in context, he is just talking about Avengers: Endgame so likely just Quantum Realm travel. This causes a problem with the returning of the stones, because it would mean you cannot just revisit certain points in the past.
 * It's unclear if, by the time he gets to "If you go back to the past, you simply created a new reality", he is still referring to "what Hulk said" or has moved on, because Hulk did not clearly refer to alternate realities unless you try to read into his comments to make it sound like alternate realities.
 * New realities are created, not existing on their own.
 * Joe Russo: "The characters in this movie created new timelines when they went back to the past, but it had no effect to the prime universe. What happened in the past 22 movies was still canon."
 * This part alone does not necessarily mean that every jump to the past created new timelines, only that at least some did. But with the parts above, it would imply it's every jump.
 * If every jump into the past created a branch in time, it would be impossible to safely return the Infinity Stones. Steve would arrive at each point and just cause a split branch on the branch, one where he returned the Infinity Stone, still leaving behind a dark branch. This goes completely against Bruce saying that the science supports them being able to make sure there are no dark timelines, and the idea of returning the Infinity Stones, unless there is some way in which he could return them without physically arriving.
 * He reiterates the point about being unable to rewrite time and therefore change the main timeline.
 * Xiang Rong: "How would Cap react when he encounters Red Skull when he returned the stone?"
 * Joe Russo: "Red Skull would probably put the Soul Stone back to its location, and wait for the next unfortunate stone-seeker to make a sacrifice. Cap and Red Skull probably won't fight. It's because it's his mission to return the stone to its original place. The Red Skull is also no longer the same Red Skull from The First Avenger. He is more like a ghost, you could almost say he's a completely different entity now. He only exists to guard the stone, his past conscious may or may not exist anymore.
 * This implies that Captain America would indeed have to physically take the stone back to Red Skull to return it.
 * Xiang Rong: "Endgame ' s plot, is it a parallel universe or a closed time loop?"
 * Joe Russo: "Nope, not a time loop."
 * The film's "plot" is referring to the premise of the film revolving around the Time Heist. This is agreed by all parties to not be a time loop. This comment alone doesn't rule out Clint and Steve's jumps being time loops.
 * Joe Russo: "Both Ancient One and Hulk were right. You can't change the future by simply going back to past. But it's possible to create a different alternate future."
 * Saying "it's possible" would imply that it doesn't always happen, which would support that not every jump in time creates a split. However, he is saying, "It is impossible to change the future by simply going back to the past, however you create a different alternate future," so it's likely that the reason he says "possible" is simply as a synonym for "however" in counter to the talking about changing the future being "impossible", not so much to imply that it's possible to not create a different alternate future.
 * Joe Russo: "It's not butterfly effect."
 * The people involved with the film seem to define the butterfly effect as specifically rewriting the one only existing timeline. So, again, a comment about not rewriting the one only existing timeline.
 * Joe Russo: "Every decision you made in the past could potentially create a new timeline."
 * This is a strange comment. None of the discussion has been about whether decisions create a new timeline. This implies that the act itself of going back didn't create the timelines, but rather that when they arrive, they have to work in compliance with the original timeline or else a decision they make could split the timeline. This would mean that not every jump necessarily created a new timeline. However, in Avengers: Endgame, those characters after arriving in the past have to jump back - if their decisions after arrival were what split the timeline, then what happened in the main timeline to the versions of them who didn't make that decision? They can't have jumped back to 2023 because then we'd have several versions of the characters arriving through the Quantum Tunnel simultaneously following the Time Heist. But it's highly unlikely that there's several versions of the characters out there in hiding having been left behind by the Time Heist...
 * What's more likely, if you were to take this interpretation, is that the jump itself didn't create a new timeline, but the landing of the jump, the arrival in that time, was a decision that split the timeline in each situation where there was a split, so in the normal timeline nobody was ever there in, say, 2012. This would mean that 2012 and 2014, where events are very much incompatible with the original timeline, had decisions split them. But the 1940s, 1970, 2013, and 2018 would be less clear, as they are potentially compatible with the main timeline.
 * However, this comment is different from everything else in the main discussion, I'm not sure it warrants too much thought. It's quite possible Joe Russo just meant that every decision you made in the past could potentially make your new timeline very different - that something like 1970, for example, would technically still be a new timeline but negligible from the main timeline so he's not considering it a proper "new timeline", but decisions in 2012 and 2014, for example, are proper "new timeline"s.
 * Tying this into Marvel's Agents of S.H.I.E.L.D. (which he is not referring to), this could contribute for an explanation as to how the agents broke out of the loop - that in travelling back to the past, while this did not itself split the timeline, the fact that they had travelled through time essentially gave them the opportunity, somehow, to break away from the loop if their decisions made this happen.
 * Joe Russo: "For example, the old Cap at the end movie, he lived his married life in a different universe from the main one."
 * Again he says that this is not the main timeline but a different one. Also, even if we are to put stock in Joe's previous comment about decisions, he here says that Steve is an example of a decision splitting the timeline, so the 1940s jump would, even by the decisions interpretation, split the timeline according to him.
 * "Alternate reality" = "different universe".
 * Previously stated that he "created an alternate reality", and now stated that "alternate reality" = "different universe", so the timeline stuff in Avengers: Endgame would have "created" different universes.
 * There is a question of in what fashion universes split. Is it a single universe up to a point in time and then it splits like a monozygotic twin or mitosis? Is it essentially a copy-and-paste of the universe at that point, two universes with an identical history but not literally a shared single history? Is it two parallel universes that that just happen to be identical up until the point when people arrive through time? The latter seems unlikely, as it would require the time travel to somehow select a universe that it is pretty much identical up until the point in time of the destination.
 * The fashion in which universes split is important for then considering the question of what happens if characters from one of the subsequent universes then goes back in time. If they go back in a causal loop, does that mean that they feature in the history of both universes? If the universes split like monozygotic twins/mitosis, then going back in time means going back to the single stem, so appears in the shared history of both. If they were then still around at the point that the universe splits, then you end up with a version of the character in each timeline as with anyone else present at the time of the split.
 * If the universe essentially copy-and-pastes, including its history, up to the point of copying, it is more complicated. The copy-and-pasted universe would then have a character going back into its history. However, the whole idea of a causal loop is that, while the perspective changes for the character moving in time, time itself is not changing and is just playing out with that character having arrived in the past. In which case, for the copy-and-pasted history to include the character having come back from the future, the original history must include that character having come back from the future, despite it being the other universe's future. Which then means that that character from the other future is around at the time of the anchor, so still around in this universe's future as well after the anchor point. So essentially, the copy-and-paste idea would function almost identically to the idea of a monozygotic/mitosis split, albeit just with the idea of them still being distinct universes and always having been, just identical up to a point for this reason instead of literally the same universe. After all, the "copy-and-paste" phrasing I have used may be slightly misleading, as it implies the universe only comes into existence at a certain point. While that universe would only exist through being "created" from the main universe, it would still have its own full history of time so would have always existed, only this would be its reason for existing. So there would be no before and after with the copy-and-paste, it would more be like the two universes' histories are in sync. Essentially, this explanation doesn't particularly make sense, because it would require the main universe to have a character from another universe in it without that character ever crossing between universes or being in some stem timeline.
 * The third option, just two universes happening to be identical up to the point of the change, has the same problem. It is essentially the same as the second option when it comes to this problem, the only difference being the reason for these universes existing - in this case, the universes are just entirely separate, but have to be identical. To have an identical history, you would require the character to be present in both histories without any reason to be existing in the main universe's past. So, if causal loop time travel is possible (which seems true from at least some of this), this means that, most likely, the fashion in which universes split should be the monozygotic/mitosis manner.
 * Joe Russo: "He had to make another jump back to the main universe at the end to give the shield to Sam."
 * It's unclear if by this, Joe means a Quantum Realm time jump, or just some sort of across-timeline "jump", because the former should not be possible without coming out of the Quantum Tunnel. The latter would be what has to happen, but how he does so is a mystery - which is what the Russos had previously seemingly said it is supposed to be.

April 30, 2019: The Smithsonian - Russos Q&A
https://www.cbr.com/avengers-endgame-russos-mcu-time-travel-rules/

Quote

 * Reporter: "Joe Russo pointed to two explanations of time travel in the MCU, one from Banner and the other from the Ancient One. Every action the heroes commit while in the past would result in the formation of a divergent timeline, or alternate reality, as a sort of butterfly effect. With that in mind, the Ancient One warns Banner to return the Infinity Stones to their proper places in the main timeline to ensure the trillions of lives in each of the divergent realities would be spared from the Avengers' tampering and continue to exist."
 * Reporter: "At the end of the film, with Captain America deciding to travel back to the 1940s, to a point when the prime version of himself had been frozen, and reunite with Peggy Carter, he created a divergent timeline in which the two marry and grow old together. The question remains how Steve Rogers was able to return to the main timeline decades later, and with an intact vibranium shield to give to Sam Wilson. For Anthony Russo, the concept of the divergent timelines gave the film, and the cinematic universe, multiple layers that he particularly enjoyed."

Quote

 * Reporter: "Joe Russo pointed to two explanations of time travel in the MCU, one from Banner and the other from the Ancient One. Every action the heroes commit while in the past would result in the formation of a divergent timeline, or alternate reality, as a sort of butterfly effect."
 * This should not be read too much into since it's the reporter relaying what was said in their own terms and not a direct quote. The wording about "every action" forming a divergent timeline if taken very strictly would be what Joe Russo casually mentioned in the previous interview about actions creating timelines, but it is more likely that the reporter is just talking about Joe Russo discussing the heroes' actions going to the past creating divergent timelines.
 * If the reporter actually means Joe Russo discussed the heroes' actions going to the past creating divergent timelines, then this would refer to the Time Heist (the actions the heroes commit much more likely meaning that than anything like Steve's choice) and not Clint and Steve.
 * Divergent timeline = alternate reality.
 * Reporter: "With that in mind, the Ancient One warns Banner to return the Infinity Stones to their proper places in the main timeline..."
 * Returning them to their proper place in the "main timeline" again seems like a slight mis-wording from the reporter. It's not the main timeline when they're missing. But if it was actually what they said, this would support the idea that since they cannot seemingly navigate the timelines, they only have to return the stones to the volatile points in the main timeline where a timeline threatens to split out to stop them from splitting.
 * Reporter: "... to ensure the trillions of lives in each of the divergent realities would be spared from the Avengers' tampering and continue to exist."
 * This would be them preventing the suffering, not erasing it, like Banner promised. It's just making the divergent timeline nicer because it does still have an Infinity Stone. This Russo explanation would mean that the black line shouldn't disappear, just turn orange. The only ways to reconcile this with the film are the thing I mentioned during the dissection of the Ancient One scene where you essentially ignore the black line demonstration and take a certain interpretation of Banner's words, or if you assume that the Infinity Stone-less timeline is only a branch on the branch already created by the time travel. Thus by replacing the stones you are still erasing the suffering rather than preventing it, by erasing that split, but this also doesn't strictly adhere to this comment, as it would essentially mean that you go from 50 : 50 of the two branches on the branch with good : bad to just one timeline existing, the good one. You aren't actually sparing those people in the bad split from the Avengers' tampering, you're just stopping those people affected by the tampering from existing. There's no real way to make this comment work.
 * Reporter: "At the end of the film, with Captain America deciding to travel back to the 1940s, to a point when the prime version of himself had been frozen, and reunite with Peggy Carter, he created a divergent timeline in which the two marry and grow old together."
 * Again, the Russos say this was a different timeline.
 * Reporter: "The question remains how Steve Rogers was able to return to the main timeline decades later, and with an intact vibranium shield to give to Sam Wilson. For Anthony Russo, the concept of the divergent timelines gave the film, and the cinematic universe, multiple layers that he particularly enjoyed."
 * This is pretty much a repeat of what they've been saying about how Steve's method of returning is a mystery.
 * The reporter's phrasing suggests that the reason the shield is intact is because it came from this alternate timeline.

May 3, 2019: Fandango - Markus and McFeely Interview
https://www.fandango.com/movie-news/exclusive-interview-the-avengers-endgame-writers-break-down-the-biggest-moments-in-the-movie-spoilers-753736

Quote
[...] [...]
 * Erik Davis: "Let's start with the time travel. What was your approach?"
 * Stephen McFeely: "[...] So, then, we had to decide what kind of time travel rules we were using. We brought in a couple of physicists who, to a man, said, "I'm glad you brought me in, because I've always wanted to talk to people from Hollywood to say that you know I love Back to the Future as much as the next person, but we don't think that's how it would work." Which was also helpful for us because as you can imagine, every time we went back to one of... you know we have six different time heists in three or four different periods... if every time you went back you created a new Biff's Casino, for want of a better term, right? Another crack in the version of your timeline? We would never get out of the second act. So for us the strongest thing we could do, and the most helpful thing we could do, is to operate under some kind of branch reality, so that the things that have already happened... which is what... again, it's time travel which is humanly impossible, but a number of physicists had told us it's much more likely we would operate in a branch reality than a singular timeline. So that's the floor for the time travel conversation."
 * Erik Davis: "So people are asking... Does this mean an old Captain America was hanging out this whole time while another Captain America was saving the day?"
 * Christopher Markus: "That is our theory. We are not experts on time travel, but the Ancient One specifically states that when you take an Infinity Stone out of a timeline it creates a new timeline. So Steve going back and just being there would not create a new timeline. So I reject the "Steve is in an alternate reality" theory. I do believe that there is simply a period in world history from about '48 to now where there are two Steve Rogers. And anyway, for a large chunk of that one of them is frozen in ice. So it's not like they'd be running into each other."
 * Erik Davis: "Do you think there's a world where we see the adventures of Captain and Peggy either on the big or small screen?"
 * Christopher Markus: "Possibly. I think maybe all I did was Steve was a stay-at-home dad and Peggy went to work at S.H.I.E.L.D.. I don't know that there were any adventures."

Dissecting

 * Erik Davis: "Let's start with the time travel. What was your approach?"
 * Stephen McFeely: "[...] So, then, we had to decide what kind of time travel rules we were using. We brought in a couple of physicists who, to a man, said, "I'm glad you brought me in, because I've always wanted to talk to people from Hollywood to say that you know I love Back to the Future as much as the next person, but we don't think that's how it would work." Which was also helpful for us because as you can imagine, every time we went back to one of... you know we have six different time heists in three or four different periods... if every time you went back you created a new Biff's Casino, for want of a better term, right? Another crack in the version of your timeline? We would never get out of the second act."
 * This is McFeely saying, as has been said throughout this, that you cannot rewrite the one timeline.
 * Adding that not "every time you went back" would you create "another crack in the version of your timeline" is interesting, potentially suggesting that not every jump creates a split, though in context it's likely just the way he is talking about rewriting the timeline.
 * Stephen McFeely: "So for us the strongest thing we could do, and the most helpful thing we could do, is to operate under some kind of branch reality, so that the things that have already happened... which is what... again, it's time travel which is humanly impossible, but a number of physicists had told us it's much more likely we would operate in a branch reality than a singular timeline. So that's the floor for the time travel conversation."
 * The main plot functions under branch realities, not a singular timeline. He is referring to not rewriting the singular timeline.
 * Erik Davis: "So people are asking... Does this mean an old Captain America was hanging out this whole time while another Captain America was saving the day?"
 * Christopher Markus: "That is our theory. We are not experts on time travel, but the Ancient One specifically states that when you take an Infinity Stone out of a timeline it creates a new timeline. So Steve going back and just being there would not create a new timeline. So I reject the "Steve is in an alternate reality" theory."
 * When you take a stone out, it creates an alternate timeline. If there were any doubt that that is what splitting the flow of time meant.
 * Here, Markus specifically highlights a line the Russos have not acknowledged. When you take a stone out, it creates an alternate timeline. Markus doesn't specify that that's the only way, but the italicizing in the report of the "Infinity Stone" and him then saying "So Steve going back and just being there would not create a new timeline" does imply he is saying that Infinity Stones are the only way to create a new timeline.
 * Markus is specifically rejecting the Russos' comments in saying he rejects "the "Steve is in an alternate reality" theory", because it is only said that taking an Infinity Stone creates a new timeline.
 * The removing of a stone "creates" a timeline, it's not a separately existing timeline.
 * Timeline = reality.
 * Christopher Markus: "I do believe that there is simply a period in world history from about '48 to now where there are two Steve Rogers. And anyway, for a large chunk of that one of them is frozen in ice. So it's not like they'd be running into each other."
 * Steve went back to 1948.
 * Steve just lived through the timeline again, which makes sense for why he would then be on the bench at the end. Markus also smartly says "'48", as this would line up with Marvel's Agent Carter, finishing in July 1947 with no signs of Steve coming back into Peggy's life. 1948 would then make sense, after she and Sousa have presumably broken up.
 * Steve returning to 1948 and living through this timeline would also make him Peggy's husband mentioned in Captain America: The Winter Soldier in an interview from 1953, tying up the loose end that Markus and McFeely have left in both Captain America: The Winter Soldier and Marvel's Agent Carter of who the mysterious husband was.
 * Erik Davis: "Do you think there's a world where we see the adventures of Captain and Peggy either on the big or small screen?"
 * Christopher Markus: "Possibly. I think maybe all I did was Steve was a stay-at-home dad and Peggy went to work at S.H.I.E.L.D.. I don't know that there were any adventures."
 * This would explain Steve being able to stay hidden for 75 years, and was the assumption I had personally made due to the film suggesting this was his retirement to live a "beautiful" quiet life.

May 3, 2019: Los Angeles Times - Russos Interview
https://www.latimes.com/entertainment/movies/la-et-mn-avengers-endgame-spoilers-explained-russo-brothers-20190503-story.html

Quote

 * Sonaiya Kelley: "Okay, be honest: Do you guys understand everything about how time travel works as explained in the movie or are there still loopholes even for you?"
 * Anthony Russo: "In the movie, the Hulk is very explicit about what our rules are, which is you cannot change the present by altering the past. All you can do by going to the past - and for a character like Cap[tain America], living in the past - is create an alternate future. So this is a world in which alternate timelines exist."
 * Sonaiya Kelley: "Was it difficult presenting a theory of time travel that hadn't previously been explored onscreen?"
 * Anthony Russo: "Back to the Future is one of our favorite films, and the rules of that movie are ubiquitous; they have informed pop culture for 40 years. And we wanted to do something different. We didn't realize how complicated it would be to create new rules and have people go with us, but we learned very early on in the test screenings that people are really committed to those Back to the Future rules - if you shoot yourself, you should die. We spoke with a few physicists, and there's a lot of theories about how time travel could work. We chose the multiverse theory."
 * Sonaiya Kelley: "Since Loki vanishes with the Tesseract, could he still be alive in the new timeline or would Cap returning the stones undo that?"
 * Anthony Russo: "Loki could absolutely still be alive in an alternate timeline."

Dissecting

 * Sonaiya Kelley: "Okay, be honest: Do you guys understand everything about how time travel works as explained in the movie or are there still loopholes even for you?"
 * Anthony Russo: "In the movie, the Hulk is very explicit about what our rules are, which is you cannot change the present by altering the past."
 * Here, Anthony does get right what Hulk says (assuming the next part is no longer referring to what Hulk says) without adding any extra stuff like some others in some other quotes. Simply that you cannot change things even if you're changing the past.
 * Anthony Russo: "All you can do by going to the past - and for a character like Cap[tain America], living in the past - is create an alternate future. So this is a world in which alternate timelines exist."
 * In the context of just being about this film, Anthony is making a comment about creating alternate timelines. Now, he doesn't say that you can't stay in a time loop, only that the only way of altering time is that you "can" "create an alternate future". But he adds that Captain America created an alternate future, which is the main example of where it would be in a time loop.
 * Captain America lived in an alternate future from the point of his arrival.
 * Sonaiya Kelley: "Was it difficult presenting a theory of time travel that hadn't previously been explored onscreen?"
 * Anthony Russo: "Back to the Future is one of our favorite films, and the rules of that movie are ubiquitous; they have informed pop culture for 40 years. And we wanted to do something different. We didn't realize how complicated it would be to create new rules and have people go with us, but we learned very early on in the test screenings that people are really committed to those Back to the Future rules - if you shoot yourself, you should die. We spoke with a few physicists, and there's a lot of theories about how time travel could work. We chose the multiverse theory."
 * So, timelines are indeed related to the multiverse.
 * The fact that "the multiverse theory" is described as their method of time travel would imply that time travel in the film is always multiverse-related, i.e. their decision is that time travel creates alternate universes full stop, as in every time. But there's definitely flexibility in this part of the comment for it to just mean that the multiverse theory is their choice over rewriting a singular timeline, not that multiverse is the only way time travel works ever in Avengers: Endgame.
 * Sonaiya Kelley: "Since Loki vanishes with the Tesseract, could he still be alive in the new timeline or would Cap returning the stones undo that?"
 * Anthony Russo: "Loki could absolutely still be alive in an alternate timeline."
 * So according to this, the Avengers did not in fact manage to keep their promise and get rid of any timeline damage? This comment would imply that a) the timeline still exists, and b) has substantial changes which the Avengers have not rectified.

May 6, 2019 (from April 30, 2019): The Hollywood Reporter - Russos Freer Gallery Q&A
https://www.hollywoodreporter.com/heat-vision/avengers-endgame-directors-explain-captain-america-ending-scene-1207742

Quote

 * Anthony Russo: "If you went back to that timeline, between the point where Steve went into the ice [in Captain America: The First Avenger] yet before Peggy met her husband, Peggy was available."
 * Holmes noted that some fans have found it creepy that Steve Rogers essentially made Peggy's future relationship with her husband, as well as their two children, disappear.
 * Russo brothers: "They exist in a different timeline."
 * Anthony Russo: "Here's the most important thing about time travel: It doesn't exist."
 * Joe Russo: "According by the rules of the movie, as stated by the Hulk and by the Ancient One, we go to great pains to tell you that Back to the Future is bulls**t. The Hulk says if you're in the present and you go back to the past, you cannot affect the present because it has already occurred. That now becomes your past. Right? And if you're [currently] in the past, this is now your present. And anything you do in that time shift would create a multiverse reality. It will create a new future, but it's not going to affect your past."

Dissecting

 * Anthony Russo: "If you went back to that timeline, between the point where Steve went into the ice [in Captain America: The First Avenger] yet before Peggy met her husband, Peggy was available."
 * Sounds like if you go by the Russos, Steve went back somewhere between February 1945 (at least September really, since that is when It's Been a Long, Long Time was released) and Peggy meeting her husband, which is no later than 1953, by which time they are married.
 * Holmes noted that some fans have found it creepy that Steve Rogers essentially made Peggy's future relationship with her husband, as well as their two children, disappear.
 * Russo brothers: "They exist in a different timeline."
 * Again, the Russo explanation.
 * Anthony Russo: "Here's the most important thing about time travel: It doesn't exist."
 * Joe Russo: "According by the rules of the movie, as stated by the Hulk and by the Ancient One, we go to great pains to tell you that Back to the Future is bulls**t."
 * Just another reiteration of the idea of not rewriting one single timeline.
 * Joe Russo: "The Hulk says if you're in the present and you go back to the past, you cannot affect the present because it has already occurred. That now becomes your past. Right? And if you're [currently] in the past, this is now your present."
 * That's all true, correct, and fine.
 * Joe Russo: "And anything you do in that time shift would create a multiverse reality. It will create a new future, but it's not going to affect your past."
 * Here, Joe is saying that any action once shifted into the past creates a multiverse reality new future. This goes again slightly into the idea of it being actions that split the timeline and not their arrival, but them just being there is likely what he means.
 * Again, the multiverse appears to be related at least in part to alternate timelines.

May 6, 2019: Business Insider - Russos Interview
https://www.businessinsider.com/avengers-endgame-directors-describe-making-of-the-movie-interview-2019-5?r=US&IR=T

Quote

 * Travis Clark: "At the end, when Cap brings the stones back in time, does he correct all the timelines that got screwed up? Is there a past Loki still out there?"
 * Joe Russo: "The intent was that he was going to correct the past timelines at the point that the stones left. Loki, when he teleports away with the Time Stone, would create his own timeline. It gets very complicated, but it would be impossible for [Cap] to rectify the timeline unless he found Loki. The minute that Loki does something as dramatic as take the Space Stone, he creates a branched reality."
 * Anthony Russo: "We're dealing with this idea of multiverses and branched realities, so there are many realities."
 * Travis Clark: "So by that logic, Cap basically created a new timeline for himself when he went back?"
 * Joe Russo: "Correct, so he would have to come back to this timeline in order to hand off the shield."
 * Anthony Russo: "There's a question of, how did this separate timeline Cap come to reappear in this timeline and why?"
 * Travis Clark: "And that's a story for another day?"
 * Joe Russo laughs.
 * Joe Russo: "Correct."

Dissecting

 * Travis Clark: "At the end, when Cap brings the stones back in time, does he correct all the timelines that got screwed up? Is there a past Loki still out there?"
 * Joe Russo: "The intent was that he was going to correct the past timelines at the point that the stones left."
 * "Correct"? It's unclear exactly what this would mean, it doesn't seem to be the same as erasing, but Joe doesn't clarify what correcting is.
 * Joe Russo: "Loki, when he teleports away with the Time Stone, would create his own timeline."
 * He means the Space Stone.
 * This again appears to be Joe Russo implying that an action is what creates a new timeline, though it might be just poor wording and he means either that at that point the timeline is properly different from the normal timeline or that at that point the timeline is not correctable, whatever he means by "correct".
 * Joe Russo: "It gets very complicated, but it would be impossible for [Cap] to rectify the timeline unless he found Loki."
 * This implies that Steve is essentially trying to make every timeline be as unchanged as possible, not erasing the timelines as said in the film.
 * If Steve is only rectifying them, it's odd that, if this is the intention in the film, they talk about how they'll clip all the branches, if they know they can't.
 * This would mean that the 2012 timeline in some way persists. The Russos' comments would imply all the timelines persist, just rectified in some way, but at the very least this would imply the 2012 timeline persists.
 * Joe Russo: "The minute that Loki does something as dramatic as take the Space Stone, he creates a branched reality."
 * Joe again makes a muddled comment about it just being actions that create a branched reality, while also suggesting that time in some way relies on "dramatic" actions. Again, this only makes some sense if you understand him to mean either that only at that point is the branched reality actually no longer negligibly different, or that it only at that point is unable to corrected/rectified in whatever sense that's supposed to mean.
 * Anthony Russo: "We're dealing with this idea of multiverses and branched realities, so there are many realities."
 * This would suggest the realities are still around.
 * Travis Clark: "So by that logic, Cap basically created a new timeline for himself when he went back?"
 * Joe Russo: "Correct, so he would have to come back to this timeline in order to hand off the shield."
 * The Russo comment again about Cap creating a new timeline and returning to hand off the shield.
 * Anthony Russo: "There's a question of, how did this separate timeline Cap come to reappear in this timeline and why?"
 * Travis Clark: "And that's a story for another day?"
 * Joe Russo laughs.
 * Joe Russo: "Correct."
 * The Russos again seem to admit there is a gap in the logic of how that would work, but imply that that is intentional and has an explanation, therefore that it's not a mistake in their logic.

May 6, 2019: CinemaBlend - Russos Interview
https://www.cinemablend.com/news/2471308/the-russo-brothers-confirm-a-major-captain-america-theory-we-had-after-avengers-endgame

Quote

 * Joe Russo: "He would have to encounter Red Skull."

Dissecting

 * Joe Russo: "He would have to encounter Red Skull."
 * This again suggests Steve has to physically go and return all the stones.

May 7, 2019: Comic Book - Russos Interview
https://comicbook.com/marvel/2019/05/07/avengers-endgame-confirms-multiverses-joe-russo-time-travel/

Quote

 * Joe Russo: "What's most compelling is that this is a multiverse. But that is what's most interesting. You've seen everything else, everything else about being looped in time or whatever, you've seen it all. What's really interesting is that you create multiple timelines and it's said in the movie twice. If you're paying attention to what the characters are saying, they're each talking from their own perspective. Banner is a man of science and when he's explaining to everyone in that room why movies are wrong, he's talking about it from quantum physics standpoint. He says that if you leave the present to go to the past then that present has become your past. It has always happened. You can't change it by influencing the past. What happens is you then create a new future by going into the past. So, you have to travel to the past, come back to that present and then fix it moving forward because you can't alter it from back there. So, by necessity, by logic, you then create - if you were to stay back there - you would create an alternate timeline."

Dissecting

 * Joe Russo: "What's most compelling is that this is a multiverse."
 * Again, the multiverse is indeed related to timelines.
 * Joe Russo: "But that is what's most interesting. You've seen everything else, everything else about being looped in time or whatever, you've seen it all. What's really interesting is that you create multiple timelines and it's said in the movie twice."
 * Hulk doesn't explicitly talk about alternate timelines. He says you can't change a timeline and then mentions a "new future" in relation to talking about changing time, which can be interpreted as either a new future from your perspective, since, say, 2012-2023 is now in your future and not your past, or literally a new future. Joe's comment here would imply it's the latter, for that scene to also be about alternate timelines. However, Joe doesn't here say that every jump is a timeline, just that during the Avengers' time travel they've created multiple timelines.
 * Joe Russo: "If you're paying attention to what the characters are saying, they're each talking from their own perspective. Banner is a man of science and when he's explaining to everyone in that room why movies are wrong, he's talking about it from quantum physics standpoint. He says that if you leave the present to go to the past then that present has become your past. It has always happened. You can't change it by influencing the past."
 * Simply, you can't change time, you can't rewrite a timeline.
 * Joe Russo: "What happens is you then create a new future by going into the past."
 * This comment implies that simply the act of going to the past creates a new timeline, regardless of other factors like Infinity Stone removal.
 * Joe Russo: "So, you have to travel to the past, come back to that present and then fix it moving forward because you can't alter it from back there."
 * Again, you can't rewrite the timeline.
 * Joe Russo: "So, by necessity, by logic, you then create - if you were to stay back there - you would create an alternate timeline."
 * Joe seems to feel that if you went back to the past, because you cannot change the timeline, you would have to create an alternate timeline by necessity. The comment about it being if you stay there is unclear, because there is no particular reason why the timeline would wait a while and then go, "Okay, now I'll split." He doesn't acknowledge the possibility of going back in time and not changing time by doing that.

May 10, 2019: The Hollywood Reporter - Markus and McFeely Interview
https://www.hollywoodreporter.com/heat-vision/avengers-endgame-writers-confirm-captain-america-fan-theory-1209241

Quote

 * Patrick Shanley: "In Winter Soldier, we establish that Peggy Carter was married and she had two kids."
 * Christopher Markus: "Yes."
 * Patrick Shanley: "We now know that Cap went back in time and married Peggy Carter. Is that the same Cap, was it always him?"
 * Stephen McFeely: "That is... Some conversation to be had on this. Quantum physics works in interesting ways and what Marvel chooses to do is not up to us, but..."
 * Christopher Markus: "... We like your idea."
 * Patrick Shanley: "Really? Alright."
 * Stephen McFeely: "It was our intention that he was always the father of those two children."
 * Patrick Shanley: "Awh."
 * Stephen McFeely: "Yeah."
 * Patrick Shanley: "That's very sweet."
 * Stephen McFeely: "But again, there are time travel loopholes for that, or, would require time travel loopholes."

Dissecting

 * Patrick Shanley: "In Winter Soldier, we establish that Peggy Carter was married and she had two kids."
 * Christopher Markus: "Yes."
 * Patrick Shanley: "We now know that Cap went back in time and married Peggy Carter. Is that the same Cap, was it always him?"
 * Stephen McFeely: "That is... Some conversation to be had on this. Quantum physics works in interesting ways and what Marvel chooses to do is not up to us, but..."
 * It would seem that the writers are not clued in on what Marvel want to do with the grey area of time travel in the film, while they can still express what their intention was and what the film is supposed to express, as it is their writing. So it's been somewhat intentionally left for Marvel to exploit the non-explicit nature.
 * Christopher Markus: "... We like your idea."
 * Patrick Shanley: "Really? Alright."
 * Stephen McFeely: "It was our intention that he was always the father of those two children."
 * So, the film is written with the intention that Steve remains in the same timeline when he goes back, creating a predestination paradox where he was always around in hiding.
 * It might not have been their intention all along for Steve to be the husband, but it was at least their intention in this film for the gap to be exploited and that to be the case.
 * Steve would then be the husband that Peggy alludes to in 1953, assuming that man is the father of her children, thus meaning he goes back to no later than 1953.
 * Patrick Shanley: "Awh."
 * Stephen McFeely: "Yeah."
 * Patrick Shanley: "That's very sweet."
 * Stephen McFeely: "But again, there are time travel loopholes for that..."
 * Not exactly sure what McFeely is saying here. If he is saying that there are time travel loopholes which allow this to be the case - you don't need loopholes, the precedent is in the film - or if he means that there are loopholes in that explanation, which isn't completely airtight.
 * One possibility is that he might instead mean that there are time travel loopholes in the way they've written it, intentionally left in there for Marvel to use.
 * Stephen McFeely: "... Or, would require time travel loopholes."
 * It's not clear whether McFeely is correcting himself or making a further comment here. If he's correcting himself, we can ignore the last part.
 * It would seem he is saying that it would require loopholes for this explanation to work, though it does not really. But perhaps he just means loopholes they intentionally built into the film - the explanation about Infinity Stones splitting the timeline.
 * It's possible that he just means there are required time travel loopholes in the film that are left in and mean that Marvel could choose to take a different direction.

May 10, 2019: Business Insider - Sean Carroll Interview
https://www.businessinsider.com/avengers-endgame-captain-america-marries-peggy-carter-time-travel-explanation-2019-5?r=US&IR=T

Quote

 * Aylin Woodward: "Sean Carroll, one of the science advisers on the movie and a theoretical physicist from the California Institute of Technology, told INSIDER that he sides with the screenwriters on this one. Carroll thinks that Cap married Peggy in the existing Marvel Cinematic Universe, not an alternate one."
 * Sean Carroll: "I think in this case, I see no reason to doubt that [Cap's] in the same timeline. If I remember correctly, when Cap visits elderly Peggy in Captain America: The Winter Soldier, she doesn't say who she gets married to."
 * Aylin Woodward: "In the scene Carroll's referring to, we see photos of Peggy and her children, but there doesn't seem to be a father visible."
 * Sean Carroll: "She could've married Cap. That's completely plausible to me. When Cap went back to the 1970s [to retrieve the Tesseract and Pym Particles with Tony Stark], there's a picture of Steve Rogers on her desk. If she married someone else, that'd be weird."
 * Aylin Woodward: "But for Carroll, the biggest tell is how Steve appears on the bench at the end of Avengers: Endgame."
 * Sean Carroll: "Cap snuck in. He didn't materialize in the time machine, but knew when they'd be there and so just showed up at the bench at the right time."

Dissecting

 * Aylin Woodward: "Sean Carroll, one of the science advisers on the movie and a theoretical physicist from the California Institute of Technology, told INSIDER that he sides with the screenwriters on this one. Carroll thinks that Cap married Peggy in the existing Marvel Cinematic Universe, not an alternate one."
 * The science adviser says Cap married Peggy in the main timeline, not an alternate timeline.
 * Aylin Woodward: "I think in this case, I see no reason to doubt that [Cap's] in the same timeline. If I remember correctly, when Cap visits elderly Peggy in Captain America: The Winter Soldier, she doesn't say who she gets married to."
 * Carroll being a science adviser and agreeing with the writers is valuable. However, in this part he is voicing his opinion more out of feeling than science.
 * The point about hiding Peggy's husband all along does tie in with the writers' comments about exploiting that to intentionally make Steve the husband all along.
 * Aylin Woodward: "In the scene Carroll's referring to, we see photos of Peggy and her children, but there doesn't seem to be a father visible."
 * Sean Carroll: "She could've married Cap. That's completely plausible to me."
 * It is unclear here whether, when Carroll says it is "plausible", he is referring to the science/logic of the film fitting it plausibly, or still talking from the perspective of feeling from watching the story.
 * Sean Carroll: "When Cap went back to the 1970s [to retrieve the Tesseract and Pym Particles with Tony Stark], there's a picture of Steve Rogers on her desk. If she married someone else, that'd be weird."
 * Again, more of a feeling statement rather than a statement related to the science/logic of the film.
 * Carroll makes a good point here. Sure, maybe Peggy was simply divorced by 1970 and went back to having him on her desk. Maybe she just has his picture on there for the memory of her friend. But Peggy decided to move on from keeping Steve's photo in 1946, so it would be odd for it to be either of those two reasons. If she had Steve back, that would make sense, while being a way to keep a photo of him without arousing suspicion. So whatever the case, her having his picture on her desk would not particularly make sense if she married someone else in the main timeline.
 * Aylin Woodward: "But for Carroll, the biggest tell is how Steve appears on the bench at the end of Avengers: Endgame."
 * Sean Carroll: "Cap snuck in. He didn't materialize in the time machine, but knew when they'd be there and so just showed up at the bench at the right time."
 * This is indeed one of the two biggest pointers (along with the talk of Infinity Stones being what causes splits in the timeline), and it's good to know how a science adviser sees it based on the science/logic of the film.

Quote

 * Jemma Simmons: "It's times like this I wish we didn't change the timeline."

Dissecting

 * Jemma Simmons: "It's times like this I wish we didn't change the timeline."
 * What they did was "change the timeline", which goes back to the previous discussions about whether there is a specific guiding of "the timeline" into one path, more valid in some capacity than other paths. It also again is a discussion of how what they did was "change" things, not just make things turn out differently in their universe.
 * The change in the timeline was what meant Fitz could end up in an accident, which is what Simmons is bemoaning. He was no longer bound by time to end up fine until 2091. He would never have been bound by time to end up fine until 2091 if they were always in a separate universe, it's specifically that they changed the timeline that meant anything could happen to him.

May 12, 2019: SiriusXM - Russos Interview
https://www.youtube.com/watch?v=dwjLg1lLPGk&t=345s

Quote

 * Jessica Shaw: What... he's in an alternate reality so this is not like a Ray Bradbury situation?
 * Joe Russo: "Well so, so what happens is we're playing with a different form of time travel, it's the multiverse notion of time travel. We didn't want to play by the Back to the Future rules, we wanted to do something different [...] The Hulk tells you in the film, he says you cannot affect the present by going to the past, because the present has always happened. So if you go to the past the only thing you can do is create an alternate future, right? That's what Cap does, is, there's an alternate future that happens, so, he would live out that life with Peggy in an alternate future, and he would have to then get back to this timeline to hand off that shield [...] You can imagine, in your own head, another Cap story taking place in that alternate timeline."

Dissecting

 * Jessica Shaw: What... he's in an alternate reality so this is not like a Ray Bradbury situation?
 * Joe Russo: "Well so, so what happens is we're playing with a different form of time travel, it's the multiverse notion of time travel."
 * Describing specifically the method of time travel as "the multiverse notion" implies that the whole time travel is working by splitting into the multiverse, rather than it just being one element of the time travel in the film.
 * Again, the time travel is indeed related to the multiverse.
 * Joe Russo: "We didn't want to play by the Back to the Future rules, we wanted to do something different."
 * Another standard "we're not following the Back to the Future rules of rewriting the one single timeline" comment.
 * Joe Russo: "The Hulk tells you in the film, he says you cannot affect the present by going to the past, because the present has always happened."
 * That's not what he says, he says you cannot affect the present by changing the past. However, he does essentially say you can't affect the present because it's always happened, and through that, he has indirectly said that you cannot affect the present by going to the past at all, as Joe says. That's all fine, it's the same as the talking about not using Back to the Future rules.
 * Joe Russo: "So if you go to the past the only thing you can do is create an alternate future, right?"
 * The word "can" here somewhat implies that it doesn't necessarily always happen. If you go to the past, the only thing you can do to affect time is create an alternate timeline. But that doesn't rule out someone going back in time and just not affecting time. Still, in context, Joe Russo appears to just mean "what does happen is...".
 * Joe Russo: "That's what Cap does, is, there's an alternate future that happens, so, he would live out that life with Peggy in an alternate future, and he would have to then get back to this timeline to hand off that shield [...] You can imagine, in your own head, another Cap story taking place in that alternate timeline."
 * Even if there were some leniency in Joe's previous comment, the only reason leniency is being sought for is due to Cap's story, and he specifies that Cap did live in an alternate future.
 * Here, Joe again makes it clear what his stance is on Cap's story - in going back, Cap created an alternate timeline (seemingly what Joe feels happens in every jump in time in the film), and somehow got back to the main timeline.
 * The implication is that the shield is from this alternate timeline.

Quote

 * Malachi: "Leopold Fitz should not be here."
 * Jemma Simmons: "Agreed. He should be with us, back on Earth."
 * Malachi: "Earth is where he died. Over a year ago, if I'm not mistaken."

Dissecting

 * Malachi: "Leopold Fitz should not be here."
 * Jemma Simmons: "Agreed. He should be with us, back on Earth."
 * Malachi: "Earth is where he died. Over a year ago, if I'm not mistaken."
 * The Chronicoms are going after the agents because they want to learn how to change time, as is later revealed. They are pointing out that Fitz being both dead and on Kitson is evidence of time travel and changing the timeline (in whatever fashion), not cross-universe travel, which would be the case if the dead Fitz had come from another universe. They just travelled in time.

May 27, 2019: Emerson Colonial Theater - Markus and McFeely Q&A
https://www.cbr.com/christopher-markus-stephen-mcfeely-avenger-endgame-deaths-time-travel/

Quote
[...]
 * Reuben Baron: "Hughes asked about Endgame ' s final scene, in which Steve Rogers travels back in time to live a full life with Peggy Carter. Markus and McFeely and directors Joe and Anthony Russo have provided conflicting answers about whether that occurred within the main Marvel Cinematic Universe or in an alternate timeline. Although favoring the main MCU theory, Markus attempted to ease the conflict by calling the issue..."
 * Christopher Markus: "... a question with many answers."
 * Reuben Baron: "As for why Steve wouldn't, for example, stop the Kennedy assassination if he were in the main MCU, Markus passed the buck."
 * Christopher Markus: "We don't have to write that!"
 * Reuben Baron: "The writers revealed that Marvel brought in physicists to provide advice on the mechanics of time travel. The duo was happy to hear one physicist flat-out state, "Back to the Future is bulls**t!" In regard to what the destruction of the Infinity Stones means for the timeline, the writers are divided: McFeely said there..."
 * Stephen McFeely: "... could be trouble going forward..."
 * Reuben Baron: "... in regard to stability, while Markus argued that..."
 * Christopher Markus: "... the atoms are still there..."
 * Reuben Baron: "... so technically the stones' essence is still keeping time flowing normally. Fans probed about other loose ends, such as Loki's escape with the Space Stone following the Battle of New York. McFeely said the scene..."
 * Stephen McFeely: "... offered possibilities..."
 * Reuben Baron: "... to other writers. How did Steve return the Soul Stone to Red Skull?"
 * Christopher Markus: "There are times you might not like somebody but you have to give their stuff back. It could make a great one-act play!"

Dissecting

 * Reuben Baron: "Hughes asked about Endgame ' s final scene, in which Steve Rogers travels back in time to live a full life with Peggy Carter. Markus and McFeely and directors Joe and Anthony Russo have provided conflicting answers about whether that occurred within the main Marvel Cinematic Universe or in an alternate timeline. Although favoring the main MCU theory...
 * The writers again favour the main MCU theory.
 * Reuben Baron: "... Markus attempted to ease the conflict by calling the issue..."
 * Christopher Markus: "... a question with many answers."
 * This suggests that the question is again not necessarily set in stone, and up for debate.
 * Reuben Baron: "As for why Steve wouldn't, for example, stop the Kennedy assassination if he were in the main MCU...
 * This is not how a time loop works. If it were a time loop, as the writers suggest, then Steve would be unable to change anything, such as stopping the JFK assassination.
 * Reuben Baron: ... Markus passed the buck."
 * Christopher Markus: "We don't have to write that!"
 * As Markus goes on to discuss in a later interview, even without the science of the time loop preventing Steve from interfering, they still felt Steve would not interfere anyway. Markus alludes to that here.
 * Reuben Baron: "The writers revealed that Marvel brought in physicists to provide advice on the mechanics of time travel. The duo was happy to hear one physicist flat-out state, "Back to the Future is bulls**t!""
 * More standard "not Back to the Future rules" discussion.
 * Reuben Baron: "In regard to what the destruction of the Infinity Stones means for the timeline, the writers are divided: McFeely said there..."
 * Stephen McFeely: "... could be trouble going forward..."
 * Reuben Baron: "... in regard to stability, while Markus argued that..."
 * Christopher Markus: "... the atoms are still there..."
 * Reuben Baron: "... so technically the stones' essence is still keeping time flowing normally.
 * The writers again raise the idea that the Infinity Stones are keeping the flow of time intact.
 * Reuben Baron: "Fans probed about other loose ends, such as Loki's escape with the Space Stone following the Battle of New York. McFeely said the scene..."
 * Stephen McFeely: "... offered possibilities..."
 * Reuben Baron: "... to other writers."
 * Reuben Baron: "How did Steve return the Soul Stone to Red Skull?"
 * Christopher Markus: "There are times you might not like somebody but you have to give their stuff back. It could make a great one-act play!"
 * Markus implies that Steve would have to physically return the stone to Red Skull.

June 6, 2019 (recorded April 23, 2019): The Empire Film Podcast: Russos and Markus and McFeely Interviews
https://podcasts.apple.com/gb/podcast/avengers-endgame-spoiler-special-interviews-ft-russos/id507987292?i=1000440794328 21:29, 25:57, 1:16:47, 1:35:47

Quote
[...] [...] [...]
 * Stephen McFeely: "We brought a couple of physics professors in to talk about time travel and that kind..."
 * Chris Hewitt: "Oh wow."
 * Stephen McFeely: "... of stuff. Yeah."
 * Chris Hewitt: "And they were like...?"
 * Stephen McFeely: "They mostly said, I think we're quoting them, "Back to the Future ' s bulls**t.""
 * Chris laughs.
 * Stephen McFeely: "Right? So we go, "Oh really. OK good that's helpful because...""
 * Chris Hewitt: "Yeah..."
 * Stephen McFeely: "... maybe I'm getting around to your question..."
 * Chris Hewitt: "Yeah..."
 * Stephen McFeely: "You know, when you remove something from each of these - we have six MacGuffins."
 * Chris Hewitt: "Yeah, yeah."
 * Stephen McFeely: "If you were to decide that there's a ripple butterfly effect for every time you did that, you would have Biff's casino times..."
 * Chris Hewitt: "Oh god yeah."
 * Stephen McFeely: "... 6 times 6 or whatever, right? So that was not available to us. It would be so puzzling, you know, we couldn't keep all that straight."
 * Christopher Markus: "Avengers: Biff's Casino"."
 * Stephen McFeely: "... "Biff's Casino"."
 * Chris laughs.
 * Stephen McFeely: "So we decided the branch reality one was better for us in that the reality you're in always happens, you cannot alter that. If you died you died, it is what it is. But it doesn't mean that you can't go back and, you know..."
 * Chris Hewitt: "Yeah."
 * Stephen McFeely: "... heist your stones."
 * Chris Hewitt: "Heist your stones and make things branch off in..."
 * Stephen McFeely: "That's right."
 * Chris Hewitt: "... in different directions..."
 * Stephen McFeely: "That's right."
 * Chris Hewitt: "... which is really interesting. And, you know, things go wrong occasionally in these time heists. The person I feel sorriest for in this movie, and there are some major, major deaths, is the Thor whose Asgard is about to be..."
 * Stephen McFeely: "Hamerless!"
 * Chris Hewitt: "... ransacked..."
 * Christopher Markus: "Yes."
 * Chris Hewitt: "... by Dark Elves, and he has no hammer because big Thor has just gone and taken his..."
 * Stephen McFeely: "This..."
 * Christopher Markus: "But..."
 * Stephen McFeely: "... is true...."
 * Christopher Markus: "... the Aether is also gone, so theoretically the Elves, who I think can detect the Aether, should go..."
 * Chris Hewitt: ""Eh!""
 * Christopher Markus: "... "Eh," and just turn around."
 * Chris Hewitt: "They would just pass by."
 * Christopher Markus: "And dead is dead, and Loki's dead, except for in that one past reality, which I think has been erased, I don't know."
 * Joe Russo: "The time travel rules that we're playing with are that, you know, that you can create a time branch which... you know, sort of an alternate timeline based on interruption of a timeline. So it's very different than, you know, Back to the Future which is linear, right?..."
 * Chris Hewitt: "Yes."
 * Joe Russo: "... Is that you can affect your present by going back to the past. That is not the case in, sort of, you know, any sort of quantum physics approach to time travel."
 * Chris Hewitt: "Yeah, it allows you to do things like have Nebula - our Nebula, so to speak - essentially kill her..."
 * Joe Russo: "Murder herself."
 * Chris Hewitt: "Yeah, murder herself."
 * Joe Russo: "Yes."
 * Chris Hewitt: "And then she doesn't disappear, which is..."
 * Joe Russo: "That's correct."
 * Chris Hewitt: "... something that might have happened in other movies."
 * Joe Russo: "As Tony Stark says, it's..."
 * Chris Hewitt: "Yeah."
 * Joe Russo: "... "That's not how it works.""
 * Chris Hewitt: ""That's not how it works"! How much - how crazy did you drive yourselves with charts and wall charts and..."
 * Joe Russo: "Well..."
 * Chris Hewitt: "... all..."
 * Joe Russo: "... you..."
 * Chris Hewitt: "... sorts of..."
 * Joe Russo: "... you really do have to define..."
 * Anthony Russo: "Very interesting..."
 * Joe Russo: "Yeah."
 * Anthony Russo: "... question, yeah."
 * Joe Russo: "We had some..."
 * Anthony Russo: "Crazy."
 * Joe Russo: "... physicists come in, and you really do have to define your rules. The tricky part is, is that you're going against, you know, 35, 40 years of TV and film..."
 * Anthony Russo: "Narrative convention."
 * Joe Russo: "... stories that are telling it different."
 * Chris Hewitt: "Yes."
 * Joe Russo: "That are playing by a different set of rules. That was certainly the most complicated part of it. But what's interesting about it - and you know people may... savvy people may come to ask how old Cap is in this timeline at the end of the movie."
 * Chris Hewitt: "Yeah.... that is one of my questions."
 * Joe Russo: "That... that is an interesting story, isn't it?"
 * Chris laughs.
 * Anthony Russo: "Joe just brought up a question that we're not going to answer..."
 * Chris laughs.
 * Anthony Russo: "... interesting!"
 * Joe Russo: "That could be a..."
 * Chris Hewitt: "Okay."
 * Joe Russo: "... story for another time."
 * Anthony Russo: "Yeah."
 * Chris Hewitt: "Okay, interesting."
 * Joe Russo: "But, look..."
 * Chris Hewitt: "Should I ask it? Should I even just go - I'll go there and then you can do what - "How is old Cap in this timeline at the end of the movie?""
 * Joe Russo: "Well it's something that will be explained..."
 * Anthony Russo: "There's..."
 * Joe Russo: "... perhaps at some point."
 * Anthony Russo: "There's clearly, you know, in order for you to - in order for that to be, according to the rules of the movie that we set out, there's some missing story that, obviously that we're not getting in the film. We don't really want to delve into that missing story. I mean, the great thing about the MCU is, like, anything that doesn't show up on screen, anything that doesn't become text, is fodder for future storytelling."
 * Joe Russo: "He deserved to go back to her and to live that life, in an alternate timeline."

Dissecting

 * Stephen McFeely: "We brought a couple of physics professors in to talk about time travel and that kind..."
 * Chris Hewitt: "Oh wow."
 * Stephen McFeely: "... of stuff. Yeah."
 * Chris Hewitt: "And they were like...?"
 * Stephen McFeely: "They mostly said, I think we're quoting them, "Back to the Future ' s bulls**t.""
 * Chris laughs.
 * Stephen McFeely: "Right? So we go, "Oh really. OK good that's helpful because...""
 * Chris Hewitt: "Yeah..."
 * Stephen McFeely: "... maybe I'm getting around to your question..."
 * Chris Hewitt: "Yeah..."
 * Stephen McFeely: "You know, when you remove something from each of these - we have six MacGuffins."
 * Chris Hewitt: "Yeah, yeah."
 * Stephen McFeely: "If you were to decide that there's a ripple butterfly effect for every time you did that, you would have Biff's casino times..."
 * Chris Hewitt: "Oh god yeah."
 * Stephen McFeely: "... 6 times 6 or whatever, right? So that was not available to us. It would be so puzzling, you know, we couldn't keep all that straight."
 * Christopher Markus: "Avengers: Biff's Casino"."
 * Stephen McFeely: "... "Biff's Casino"."
 * Chris laughs.
 * This is all the standard discussion again of how it is not the rewriting of a singular timeline idea from Back to the Future.
 * Stephen McFeely: "So we decided the branch reality one was better for us in that the reality you're in always happens, you cannot alter that. If you died you died, it is what it is. But it doesn't mean that you can't go back and, you know..."
 * Chris Hewitt: "Yeah."
 * Stephen McFeely: "... heist your stones."
 * Chris Hewitt: "Heist your stones and make things branch off in..."
 * Stephen McFeely: "That's right."
 * Chris Hewitt: "... in different directions..."
 * Stephen McFeely: "That's right."
 * This is an uncontroversial statement, just saying that the timeline is unchangeable but it is possible to go back and create branch realities when heisting Infinity Stones.
 * Chris Hewitt: "... which is really interesting. And, you know, things go wrong occasionally in these time heists. The person I feel sorriest for in this movie, and there are some major, major deaths, is the Thor whose Asgard is about to be..."
 * Stephen McFeely: "Hamerless!"
 * Chris Hewitt: "... ransacked..."
 * Christopher Markus: "Yes."
 * Chris Hewitt: "... by Dark Elves, and he has no hammer because big Thor has just gone and taken his..."
 * Stephen McFeely: "This..."
 * Christopher Markus: "But..."
 * Stephen McFeely: "... is true...."
 * Christopher Markus: "... the Aether is also gone, so theoretically the Elves, who I think can detect the Aether, should go..."
 * Chris Hewitt: ""Eh!""
 * Christopher Markus: "... "Eh," and just turn around."
 * Chris Hewitt: "They would just pass by."
 * This part is odd as it implies that the Reality Stone and Mjolnir-less 2013 timeline still exists. This would align with a problem with the Russo explanation - that if every jump creates an alternate timeline, there is no way of going back and correcting (or erasing) the timelines. But it doesn't align with either parties' intentions, that no timelines be left behind without Infinity Stones, to fall into chaos. They are joking here, and also perhaps speculating about the hypothetical future of that timeline until Steve comes back and corrects or erases it, but it's an odd conversation.
 * Christopher Markus: "And dead is dead, and Loki's dead, except for in that one past reality, which I think has been erased, I don't know."
 * Markus brings up the idea of erasing the timelines which has been ignored in many interviews. He does seem to believe that Steve would be erasing these timelines (specifically 2012, one of the very disrupted ones, implying all of the timeliens would be erased), however the way he speaks seems to line up with other implications from the writers that there is grey area intentionally left in the film over how the branch timelines work out, and also that they are not in the loop on what Marvel want to do next - that they might exploit the grey areas and take things in certain directions.
 * Another comment implying that where Marvel takes things is still open.
 * Joe Russo: "The time travel rules that we're playing with are that, you know, that you can create a time branch which... you know, sort of an alternate timeline based on interruption of a timeline."
 * Here, Joe only says that you "can" create a branch, not that that is always the case.
 * Joe Russo: "So it's very different than, you know, Back to the Future which is linear, right?..."
 * Chris Hewitt: "Yes."
 * Joe Russo: "... Is that you can affect your present by going back to the past. That is not the case in, sort of, you know, any sort of quantum physics approach to time travel."
 * Chris Hewitt: "Yeah, it allows you to do things like have Nebula - our Nebula, so to speak - essentially kill her..."
 * Joe Russo: "Murder herself."
 * Chris Hewitt: "Yeah, murder herself."
 * Joe Russo: "Yes."
 * Chris Hewitt: "And then she doesn't disappear, which is..."
 * Joe Russo: "That's correct."
 * Chris Hewitt: "... something that might have happened in other movies."
 * Joe Russo: "As Tony Stark says, it's..."
 * Chris Hewitt: "Yeah."
 * Joe Russo: "... "That's not how it works.""
 * Chris Hewitt: ""That's not how it works"! How much - how crazy did you drive yourselves with charts and wall charts and..."
 * Joe Russo: "Well..."
 * Chris Hewitt: "... all..."
 * Joe Russo: "... you..."
 * Chris Hewitt: "... sorts of..."
 * Joe Russo: "... you really do have to define..."
 * Anthony Russo: "Very interesting..."
 * Joe Russo: "Yeah."
 * Anthony Russo: "... question, yeah."
 * Joe Russo: "We had some..."
 * Anthony Russo: "Crazy."
 * Joe Russo: "... physicists come in, and you really do have to define your rules. The tricky part is, is that you're going against, you know, 35, 40 years of TV and film..."
 * Anthony Russo: "Narrative convention."
 * Joe Russo: "... stories that are telling it different."
 * Chris Hewitt: "Yes."
 * Joe Russo: "That are playing by a different set of rules. That was certainly the most complicated part of it."
 * All standard discussion again about how this isn't just one timeline being rewritten, this doesn't work like Back to the Future.
 * Joe Russo: "But what's interesting about it - and you know people may... savvy people may come to ask how old Cap is in this timeline at the end of the movie."
 * Joe is suggesting that if you pay close attention you would ask why Cap is there, not that if you pay close attention you would work out why Cap is there, suggesting that the way Cap is there at the end is not provided in the film.
 * This comment would suggest that, since the discussion of how Infinity Stones split the timeline would mean that if you pay attention there is an explanation in the film for why Steve would be there, that discussion would not mean that Steve would not create a divergent timeline.
 * Chris Hewitt: "Yeah.... that is one of my questions."
 * Joe Russo: "That... that is an interesting story, isn't it?"
 * Chris laughs.
 * Anthony Russo: "Joe just brought up a question that we're not going to answer..."
 * Chris laughs.
 * Anthony Russo: "... interesting!"
 * Joe Russo: "That could be a..."
 * Chris Hewitt: "Okay."
 * Joe Russo: "... story for another time."
 * Anthony Russo: "Yeah."
 * Chris Hewitt: "Okay, interesting."
 * Joe Russo: "But, look..."
 * Chris Hewitt: "Should I ask it? Should I even just go - I'll go there and then you can do what - "How is old Cap in this timeline at the end of the movie?""
 * Joe Russo: "Well it's something that will be explained..."
 * Anthony Russo: "There's..."
 * Joe Russo: "... perhaps at some point."
 * Anthony Russo: "There's clearly, you know, in order for you to - in order for that to be, according to the rules of the movie that we set out, there's some missing story that, obviously that we're not getting in the film. We don't really want to delve into that missing story. I mean, the great thing about the MCU is, like, anything that doesn't show up on screen, anything that doesn't become text, is fodder for future storytelling."
 * This is the most explicit that the Russos have made it that their explanation has a hole in it but that there is an explanation intentionally left mysterious, so it's not actually a hole. This is in the context of what else they have said - in this quote alone, they don't actually specify that Cap went to an alternate timeline, they're just saying that how Steve is there at the end is not explained in the film, but later in the interview they say Cap is in an alternate timeline and have of course said that in other quotes. Also, the explanation that only removing Infinity Stones creates branches so Steve didn't create a branch would in fact be something explained within the film.
 * Joe Russo: "He deserved to go back to her and to live that life, in an alternate timeline."
 * There's the standard Russo stance being mentioned, that Steve's life with Peggy was in an alternate timeline, not the main one.

Quote

 * Enoch: "I presume Atarah wants to know how you were able to travel through time so that we may go back and save our world."
 * Jemma Simmons: "It's not that simple."
 * Atarah: "You deny that you meddled with the course of events?"
 * Daisy Johnson: "No, but we don't make a point of helping people play with time that have been trying to kill us."
 * Jemma Simmons: "It's complicated, we don't actually know how we did it."

Quote

 * Enoch: "I presume Atarah wants to know how you were able to travel through time so that we may go back and save our world."
 * Jemma Simmons: "It's not that simple."
 * Atarah: "You deny that you meddled with the course of events?"
 * Daisy Johnson: "No, but we don't make a point of helping people play with time that have been trying to kill us."
 * Jemma Simmons: "It's complicated, we don't actually know how we did it."
 * This is interesting, and would suggest that the discussion above of how the exact fashion in which the agents have "changed" time being left unclear is not missing something. The exact fashion is not entirely clear to the agents, but in some way they have "meddled with the course of events", suggesting in some way changing time, lessening the dystopian future's validity.
 * They "meddled with the course of events", not just happening to travel to another universe and back and learning enough from their experience to prevent things from happening like they did in that universe. Making sure your universe would not end up like another one would not be meddling with the course of events, since it would just be participating in your universe's course of events being the way they are. You're not actually changing anything.

June 28, 2019: FOX 5 DC - Russos Interview
https://www.youtube.com/watch?v=0cclrVWc7Vo&t=348s

Quote

 * Kevin McCarthy: "When Cap goes back..."
 * Joe Russo: "Yeah."
 * Kevin McCarthy: "... where is the Cap in that world? Like, so when he goes back to the early days, is there still another Captain America in that world?"
 * Joe Russo: "Yes, so the way that it would work - right? - is that when Captain America goes back, he would create a branch reality."
 * Kevin McCarthy: "Right."
 * Joe Russo: "OK? Now he would exist in that branch reality with a second Captain America who is frozen in ice."
 * Kevin McCarthy: "So the other Cap still exists in that world?"
 * Joe Russo: "He would..."
 * Kevin McCarthy: "So..."
 * Joe Russo: "... still..."
 * Kevin McCarthy: "... would Peggy..."
 * Joe Russo: "... exist..."
 * Kevin McCarthy: "... not..."
 * Joe Russo: "... but..."
 * Kevin McCarthy: "... know that other Cap?"
 * Joe Russo: "Well he's, that other Cap is frozen in ice at this...
 * Anthony Russo: "And Peggy..."
 * Joe Russo: "... point so..."
 * Anthony Russo: "... understood that he was dead at that point in the storytelling, 'cause Cap went back to a point in time where nobody knew he still was alive, frozen in ice."
 * Joe Russo: "Now, what's also a story for another time is of course, if he created a branch reality, he would then have to use a Pym Particle to come back..."
 * Anthony Russo: "Or..."
 * Joe Russo: "... to this reality..."
 * Anthony Russo: "... Yeah."
 * Joe Russo: "... to hand that shield off."
 * Anthony Russo: "Yeah."

Dissecting

 * Kevin McCarthy: "When Cap goes back..."
 * Joe Russo: "Yeah."
 * Kevin McCarthy: "... where is the Cap in that world? Like, so when he goes back to the early days, is there still another Captain America in that world?"
 * Joe Russo: "Yes, so the way that it would work - right? - is that when Captain America goes back, he would create a branch reality."
 * Kevin McCarthy: "Right."
 * Joe Russo: "OK? Now he would exist in that branch reality with a second Captain America who is frozen in ice."
 * Kevin McCarthy: "So the other Cap still exists in that world?"
 * Joe Russo: "He would..."
 * Kevin McCarthy: "So..."
 * Joe Russo: "... still..."
 * Kevin McCarthy: "... would Peggy..."
 * Joe Russo: "... exist..."
 * Kevin McCarthy: "... not..."
 * Joe Russo: "... but..."
 * Kevin McCarthy: "... know that other Cap?"
 * Joe Russo: "Well he's, that other Cap is frozen in ice at this...
 * Anthony Russo: "And Peggy..."
 * Joe Russo: "... point so..."
 * Anthony Russo: "... understood that he was dead at that point in the storytelling, 'cause Cap went back to a point in time where nobody knew he still was alive, frozen in ice."
 * The Russos insist again that Cap would create a branch reality.
 * Joe Russo: "Now, what's also a story for another time is of course, if he created a branch reality, he would then have to use a Pym Particle to come back..."
 * Instead of saying it's a mystery how Steve would get back, Joe seems to just explain it here. It's odd, if this is supposed to be the reveal, it's very unceremonious and in a small interview and just the method from the film. Also, it seemingly shouldn't work - the reason this was a hole in the first place was because Steve couldn't just get back with the Pym Particle.
 * Anthony Russo: "Or..."
 * Joe Russo: "... to this reality..."
 * Anthony Russo: "... Yeah."
 * Anthony stops himself, but the way he interjects suggests he would say something like, "Or some other mysterious method," but that's only speculation. Still, the fact that he says "Or..." in response to using a Pym Particle to get back would perhaps imply that that was not intended as a reveal and the emphasis is just on the fact that Steve would have to get back to the main timeline, especially since Anthony stops himself once Joe gets to saying "to this reality", leaving the Pym Particle part behind. Joe also technically doesn't say he does use a Pym Particle, only that he would (seemingly) have to.
 * Joe Russo: "... to hand that shield off."
 * Anthony Russo: "Yeah."
 * Again, technically Joe only says he comes back to the timeline so he can hand over the shield, but the way it's said would probably imply that the shield is from this supposed alternate reality.

Quote

 * Deke Shaw: "Fitz died. He died, and no one was gonna bother to, I don't know, send me a text?"
 * Alphonso Mackenzie: "It was complicated."
 * Deke Shaw: "Yeah, no kidding. Besides the fact that this completely proves my entire multiverse theory, 'cause I'm still here, there's a second Fitz! And, and you sent a team out to find him, and you didn't tell me that, either?! That's not complicated, that just sucks!"
 * Alphonso Mackenzie: "It was the call made at the time."
 * Deke Shaw: "Well, maybe you shouldn't be making the calls because that was a bad one."
 * Alphonso Mackenzie: "No, it looked like you had other priorities besides being a part of this team."
 * Deke Shaw: "Oh, this team? You mean the team that I helped bring back from the dystopian future?"

Quote

 * Deke Shaw: "Fitz died. He died, and no one was gonna bother to, I don't know, send me a text?"
 * Alphonso Mackenzie: "It was complicated."
 * Deke Shaw: "Yeah, no kidding. Besides the fact that this completely proves my entire multiverse theory, 'cause I'm still here, there's a second Fitz!"
 * The show is telling us that Deke was right, there's a multiverse, and that's why he didn't blink out of existence. The 2091 he is from wasn't literally rewritten, the same as with Avengers: Endgame establishing you cannot rewrite a timeline.
 * Deke Shaw: "And, and you sent a team out to find him, and you didn't tell me that, either?! That's not complicated, that just sucks!"
 * Alphonso Mackenzie: "It was the call made at the time."
 * Deke Shaw: "Well, maybe you shouldn't be making the calls because that was a bad one."
 * Alphonso Mackenzie: "No, it looked like you had other priorities besides being a part of this team."
 * Deke Shaw: "Oh, this team? You mean the team that I helped bring back from the dystopian future?"
 * Another comment about the future. No discussion ever of it being a different universe, in the future. It was the future, the dystopian one, that they have escaped and now they're on course for a non-dystopian future.

July 1, 2019: ACE Comic-Con - Chris Evans Q&A
https://uproxx.com/hitfix/chris-evans-captain-america-confusing-avengers-endgame/

Quote

 * Chris Evans: "You know, I'm not sure I can give you those answers. That's weak as s**t, but ask the writers."

Dissecting

 * Chris Evans: "You know, I'm not sure I can give you those answers. That's weak as s**t, but ask the writers."
 * Evans believes one should turn to the writers for an explanation, over the directors, though likely did not mean too much by his statement in terms of favouring one side of the debate.

Quote

 * Leo Fitz: "I'm very, very, very much alive."
 * Deke Shaw: "Yeah, and you look great, by the way. Younger, an-... or something. I haven't really done the math on that - but I will, 'cause it's your brain that I inherited! Oh, and I - I, uh, I - I don't wanna gloat, because technically the argument was with the other you, but, uh, you know, you being here, you prove that my multiverse theory was right, so..."

Dissecting

 * Leo Fitz: "I'm very, very, very much alive."
 * Deke Shaw: "Yeah, and you look great, by the way. Younger, an-... or something. I haven't really done the math on that - but I will, 'cause it's your brain that I inherited! Oh, and I - I, uh, I - I don't wanna gloat, because technically the argument was with the other you, but, uh, you know, you being here, you prove that my multiverse theory was right, so..."
 * The fact that Fitz can be here, rather than stuck out in space, proves Deke's point that he made to the other Fitz about how multiple timelines exist, spinning out into the cosmos - his multiverse theory. If there were only one timeline, he would be stuck out in space, unless they had actually rewritten that timeline, which is impossible and also would mean Deke wasn't here with them.

July 19, 2019: San Diego Comic-Con 2019 - Writing Avengers: Endgame Panel (Markus and McFeely Interview)
https://www.youtube.com/watch?v=vtkXuQDnqfM 23:30, 28:17, 30:06, 39:02, 46:40

Quote
[...] [...] [...] [...]
 * Stephen McFeely: "If you operated by Back to the Future rules, every time you went back, and came back, you would have a new Biff's casino, right? [...] So, you can imagine that if every time, a new universe was created, we would get nowhere and we wouldn't know how to solve any one because which one did what? It was not helpful to us and we were worried that maybe we couldn't even do this idea. But we brought legit physicists in, quantum physicists, who said, "It probably doesn't work that way as much as I love that movies, it probably works this way, if it works," 'cause again..."
 * Christopher Markus: "... Which it doesn't."
 * Stephen McFeely: "... it doesn't. So the idea of branch realities, of quantum travel..."
 * Christopher Markus: "We had to boil our time rules down to something, and it came down to the stones, the stones are going to hold the universe in place. Take 'em out, things start happening. And, again, this is the pleasure of having this universe to deal with, we needed someone to explain it. Who's the most entertaining explainer in the Marvel universe? Let's get Tilda!"
 * Jeff Goldsmith: "Did you ever decide that there was maybe a moment you were gonna get into the multiverse?"
 * Stephen McFeely: "It clearly exists, right? Because Doctor Strange has talked all about it. I mean that's, it's part of the fabric of that. We may not - this may be where I disagree with Marvel or where they're going, I have no idea where Kevin Feige is going, I don't know what's happening tomorrow, I have no idea."
 * Christopher Markus: "Are you okay?"
 * Stephen McFeely: "But I'm a big believer in stakes, and if you tell me that I can just go and get another Natasha and another Tony and we can keep rolling, then particularly my grandma is gonna go, "Well why did I watch that?" So yeah we are retraining the audience all the time. There may be - I may be wrong 2 years from now where people want, "I want all sorts of stories from people I already lost.""
 * Christopher Markus: "Well particularly in a movie where we are very much heading towards some final resolutions, toward things ending, toward people leaving. If you go, "Yeah but there's seventy-five Tonys out there, like seventy-five billion Tonys out there," your drama is gonna suffer."
 * Christopher Markus: "I think you would have... There's a fascinating one act play to be written of just Steve turning up and talking to the Red Skull."
 * Jeff Goldsmith: "I wanna just set the record straight."
 * Stephen McFeely: "Yup."
 * Jeff Goldsmith: "Are there actually two physical Captain Americas living on Earth..."
 * Stephen McFeely: "Oh for...!"
 * Jeff Goldsmith: "... in the same timeline at the same time, so that during the Battle of New York. while hooded Cap is in New York, the other Cap is all the way across the country on pebble beach, having a round of golf with his family?"
 * Stephen McFeely: "Pass!"
 * Christopher Markus: "Okay... Cap doesn't golf."
 * Jeff Goldsmith: "Okay, okay. But are there, are there two Caps on Earth, would you agree to that?"
 * Christopher Markus: "I - there are varying theories... I am much very entertained by that theory."

Dissecting

 * Stephen McFeely: "If you operated by Back to the Future rules, every time you went back, and came back, you would have a new Biff's casino, right? [...] So, you can imagine that if every time, a new universe was created, we would get nowhere and we wouldn't know how to solve any one because which one did what? It was not helpful to us and we were worried that maybe we couldn't even do this idea. But we brought legit physicists in, quantum physicists, who said, "It probably doesn't work that way as much as I love that movies, it probably works this way, if it works," 'cause again..."
 * Christopher Markus: "... Which it doesn't."
 * Stephen McFeely: "... it doesn't."
 * Standard "It's not like Back to the Future" statements.
 * Stephen McFeely: "So the idea of branch realities, of quantum travel..."
 * Branch realities are involved, which is not contested.
 * Christopher Markus: "We had to boil our time rules down to something, and it came down to the stones, the stones are going to hold the universe in place. Take 'em out, things start happening."
 * Markus is saying that the time rules in Avengers: Endgame relate to the Infinity Stones, and the fact that the "time rules" "boil [...] down" to this very much implies the time rules relate solely to the Infinity Stones. And then if you take them out, things start happening to time.
 * Christopher Markus: "And, again, this is the pleasure of having this universe to deal with, we needed someone to explain it. Who's the most entertaining explainer in the Marvel universe? Let's get Tilda!"
 * Markus is saying that this is what was explained in the Ancient One scene.
 * Jeff Goldsmith: "Did you ever decide that there was maybe a moment you were gonna get into the multiverse?"
 * Stephen McFeely: "It clearly exists, right? Because Doctor Strange has talked all about it. I mean that's, it's part of the fabric of that. We may not - this may be where I disagree with Marvel or where they're going, I have no idea where Kevin Feige is going, I don't know what's happening tomorrow, I have no idea."
 * Christopher Markus: "Are you okay?"
 * Stephen McFeely: "But I'm a big believer in stakes, and if you tell me that I can just go and get another Natasha and another Tony and we can keep rolling, then particularly my grandma is gonna go, "Well why did I watch that?" So yeah we are retraining the audience all the time. There may be - I may be wrong 2 years from now where people want, "I want all sorts of stories from people I already lost.""
 * Christopher Markus: "Well particularly in a movie where we are very much heading towards some final resolutions, toward things ending, toward people leaving. If you go, "Yeah but there's seventy-five Tonys out there, like seventy-five billion Tonys out there," your drama is gonna suffer."
 * Markus and McFeely seemingly are discussing how they did not want the film to be establishing a multiverse. This could mean that timelines do not count towards the multiverse, only entirely separate universes, for whatever reason. it could refer to the idea of erasing the timelines.
 * They seem to suggest that the time travel did not contribute to the multiverse, which could refer to the idea of erasing the timelines.
 * McFeely comments again how they are not clued in on the future of the MCU, so these are just their intentions and not necessarily the direction of the MCU.
 * Christopher Markus: "I think you would have... There's a fascinating one act play to be written of just Steve turning up and talking to the Red Skull."
 * While Markus here does not say that Steve necessarily did have to turn up and talk to Red Skull, he implies it.
 * Jeff Goldsmith: "I wanna just set the record straight."
 * Stephen McFeely: "Yup."
 * Jeff Goldsmith: "Are there actually two physical Captain Americas living on Earth..."
 * Stephen McFeely: "Oh for...!"
 * Jeff Goldsmith: "... in the same timeline at the same time, so that during the Battle of New York. while hooded Cap is in New York, the other Cap is all the way across the country on pebble beach, having a round of golf with his family?"
 * Stephen McFeely: "Pass!"
 * McFeely acknowledges the disagreement between him, along with Markus, and the directors, joking about how the problem.
 * Christopher Markus: "Okay... Cap doesn't golf."
 * Jeff Goldsmith: "Okay, okay. But are there, are there two Caps on Earth, would you agree to that?"
 * Christopher Markus: "I - there are varying theories... I am much very entertained by that theory."
 * Markus expresses his partiality to the time loop theory, while saying this does not mean it is the only interpretation available or the definitive canon.

July 19, 2019: San Diego Comic-Con 2019 - A Conversation with the Russo Brothers Panel (Russos Interview)
https://www.youtube.com/watch?v=wGILJZok8tA&t=660s

Quote

 * Anthony Russo: "You know, the sort of alternate reality question - I know there's many different theories about sort of how this stacks up and I know Chris and Steve [McFeely] were just talking about some of them."
 * Joe Russo: "Don't go there!"
 * Anthony laughs.
 * Anthony Russo: "Steve [Rogers] could, you know, depending on how - where you go with the alternate realities, Steve can do a lot of things, like he can go rescue Bucky from Hydra. He could get - route Hydra out of S.H.I.E.L.D.. He could go find himself in the ice."

Dissecting

 * Anthony Russo: "You know, the sort of alternate reality question - I know there's many different theories about sort of how this stacks up and I know Chris and Steve [McFeely] were just talking about some of them."
 * Joe Russo: "Don't go there!"
 * Anthony laughs.
 * They, too, joke about the fact that there's a problem with them disagreeing.
 * Anthony Russo: "Steve [Rogers] could, you know, depending on how - where you go with the alternate realities, Steve can do a lot of things, like he can go rescue Bucky from Hydra. He could get - route Hydra out of S.H.I.E.L.D.. He could go find himself in the ice."
 * Anthony implies that they stand by Steve being in an alternate reality, but also suggests that "where you go" with Steve is still open and this is just one possibility they favour.

July 19, 2019: Backstory - Markus and McFeely Interview
Backstory: Issue 37 - Avengers: Endgame - The Writers, page 8, 11, 13, 13 (https://viewer.aemmobile.adobe.com/index.html#project/a1b0c9ac-493d-4fbb-8986-4c0b26240f0d/view/Backstory_Issue_37-5b2PM4HPP/article/Cover_Story_Avengers_Endgame_The_Writers-tory_Issue_37-ywm9RqehP)

Quote
[...] [...] [...]
 * Stephen McFeely: "We had a couple physicists come in, because Chris' research found that some of these Collider-type experiments noted that at the quantum level the same particle can exist in two places at once. And we went, "Ah, that's awesome." Then when we brought those physicists in, they kind of said Back to the Future is bulls**t. They don't look at our existence as one singular timeline, they much more embrace a branch reality version of time travel - which helps us, to be honest, because we had so many second-act missions to different times. If those created a ripple in the timeline, you'd have an exponential number of Biff's casinos. We needed a cleaner version of time travel, which meant we had to educate our audience to not assume a different version."
 * Jeff Goldsmith: "Ray Bradbury's classic time-travel short story The Sound of Thunder sets down a concept many writers have used since - that an alteration in the past can permanently change the future. Does Cap fighting Cap and then not returning to lead a different life with Agent Carter create ripples and problems in the timeline? Were there consequences to what Cap did?"
 * Stephen McFeely: "Here's how we reconcile it. We think that there have always been two Caps from 1945 to, say, now, and we just didn't know that. That's the loop, right? Again, it's not Back to the Future rules, it's branch reality rules. This is not stepping on a butterfly that turns the world into Biff's casino. You can't alter your future by going back to the past. We sort of created our own time travel rules wherein, as the Ancient One says, if you remove an Infinity Stone from a timeline, that creates a branch reality. We think Steve went back, put all the stones back, clipped those branches. Those are fine. And after he did the last one, he jumped to 1948 and decided to stay. So, his younger self is on ice somewhere and it's only in 2011 that there are technically two Steves running around - to the point where if you were to look closely at Peggy's funeral, there'd be an old man in the back named Roger Stevens."
 * Jeff Goldsmith: "Wait, is that a thing? If people rewind Civil War, would they see an old version of him at the funeral?"
 * Stephen McFeely: "No, no, no, no, no."
 * Christopher Markus: "But feel free to legally download Civil War and investigate."
 * Jeff Goldsmith: "Would having a family with Peggy put the world at risk because Agent Carter might not be fighting Hydra as much?"
 * Stephen McFeely: "That dance you see takes place sometime after the second season of Agent Carter."
 * Jeff Goldsmith: "What would you tell the people asking about where Thor's hammer, Mjolnir, is?"
 * Stephen McFeely: "I think he brought it back to Asgard."
 * Christopher Markus: "He gave it back to the Thor of that time."
 * Stephen McFeely: "Which was actually probably unnecessary if you take the stone because you're going to erase that time - that branch where he doesn't have it anyway."
 * Jeff Goldsmith: "Did you map out where Loki goes after he grabs the Tesseract in 2012?"
 * Stephen McFeely: "TBD."
 * Christopher Markus: "Probably to cause some havoc in Asgard."
 * Stephen McFeely: "It's probably mischief."
 * Jeff Goldsmith: "But if he has escaped a branched timeline before it was destroyed, would that inspire a new movie that reconciles what Loki does with the Tesseract?"
 * Stephen McFeely: "Listen, we don't work at Marvel, man. I don't know."

Dissecting

 * Stephen McFeely: "We had a couple physicists come in, because Chris' research found that some of these Collider-type experiments noted that at the quantum level the same particle can exist in two places at once. And we went, "Ah, that's awesome." Then when we brought those physicists in, they kind of said Back to the Future is bulls**t. They don't look at our existence as one singular timeline..."
 * Standard talk about Back to the Future.
 * Stephen McFeely: "... they much more embrace a branch reality version of time travel..."
 * Specifically referring to the "version of time travel" as "branch reality" implies that the jumps in time themselves create branches.
 * Stephen McFeely: "... which helps us, to be honest, because we had so many second-act missions to different times. If those created a ripple in the timeline, you'd have an exponential number of Biff's casinos. We needed a cleaner version of time travel, which meant we had to educate our audience to not assume a different version."
 * Again, just discussing how each individual change in the past does not ripple through and rewrite the singular timeline.
 * Jeff Goldsmith: "Ray Bradbury's classic time-travel short story The Sound of Thunder sets down a concept many writers have used since - that an alteration in the past can permanently change the future. Does Cap fighting Cap and then not returning to lead a different life with Agent Carter create ripples and problems in the timeline? Were there consequences to what Cap did?"
 * This is poorly worded, but I believe he is essentially just asking whether Cap's actions had some sort of consequence ripple effect on time.
 * Stephen McFeely: "Here's how we reconcile it. We think that there have always been two Caps from 1945 to, say, now, and we just didn't know that. That's the loop, right?"
 * Describing the time loop the writers believe in.
 * Interestingly, McFeely says 1945 here when they've previously said 1948. 1945 would be problematic due to Marvel's Agent Carter.
 * Stephen McFeely: "Again, it's not Back to the Future rules, it's branch reality rules. This is not stepping on a butterfly that turns the world into Biff's casino. You can't alter your future by going back to the past."
 * It's a little odd that McFeely talks about the branch realities here again, when that is not particularly relevant to the case they're making about Steve. I would imagine that he's bringing it up simply to mean, "It's not Back to the Future rules, you can't change your past (the only way you can change time is through branches)," to then say that Steve thus wouldn't have changed time.
 * Again, not Back to the Future butterfly effect rules.
 * Stephen McFeely: "We sort of created our own time travel rules wherein, as the Ancient One says, if you remove an Infinity Stone from a timeline, that creates a branch reality."
 * McFeely lays this out as the rules they established. Simply that removing an Infinity Stone from a timeline creates a branch, no other reason.
 * Stephen McFeely: "We think Steve went back, put all the stones back, clipped those branches. Those are fine."
 * McFeely says that Steve "clipped" the branches, like the film. This would imply cutting off certain branches, through erasing or simply slicing off in some form. However, "Those are fine" is more ambiguous, as it could fit with the idea more of just fixing each branch, putting things on the right course.
 * Stephen McFeely: "And after he did the last one, he jumped to 1948 and decided to stay."
 * "1948" again. "1945" can be taken as just a slip-up.
 * Stephen McFeely: "So, his younger self is on ice somewhere and it's only in 2011 that there are technically two Steves running around - to the point where if you were to look closely at Peggy's funeral, there'd be an old man in the back named Roger Stevens."
 * McFeely describes the time loop they believe is in play. All in all, this comment says that you cannot change time, so when Steve went back he simply stayed in time (he didn't remove an Infinity Stone so no branch was created), arriving in 1948 and living through to now. For 63 of those years, his younger self is frozen, so only from 2011 is there two Steves both out in the world.
 * Steve would have changed his identity ("Roger Stevens" is a joke but indicates that he changed his identity) when living in the main timeline.
 * Jeff Goldsmith: "Wait, is that a thing? If people rewind Civil War, would they see an old version of him at the funeral?"
 * Stephen McFeely: "No, no, no, no, no."
 * Christopher Markus: "But feel free to legally download Civil War and investigate."
 * They confirm that the theory of the old man pallbearer being older Steve is incorrect, but nonetheless that older Steve would be present - just not shown on-camera.
 * Jeff Goldsmith: "Would having a family with Peggy put the world at risk because Agent Carter might not be fighting Hydra as much?"
 * Stephen McFeely: "That dance you see takes place sometime after the second season of Agent Carter."
 * Again, "1945" can be taken as merely a slip-up. This also confirms that the date was intentionally chosen to be after Marvel's Agent Carter: Season 2, the last major chronological appearance of Peggy before bits and pieces through the years, thus meaning there is no conflict with the events of Marvel's Agent Carter with this being the same timeline.
 * Jeff Goldsmith: "What would you tell the people asking about where Thor's hammer, Mjolnir, is?"
 * Stephen McFeely: "I think he brought it back to Asgard."
 * Christopher Markus: "He gave it back to the Thor of that time."
 * This aligns with the film more than the jokey comment before about a timeline where Thor is "hammerless". It can, therefore, be taken that that comment was indeed just a joke and this is the intention. So, according to the writers, Steve returned Mjolnir to that Thor.
 * Stephen McFeely: "Which was actually probably unnecessary if you take the stone because you're going to erase that time - that branch where he doesn't have it anyway."
 * McFeely touches on the erasing of the timelines, something mentioned in the film but rarely touched on in interviews. McFeely here says that Steve would be erasing that time when he returns the Reality Stone. There is a slight wiggle room here, to take it as, instead of meaning "You're going to erase that time anyway", rather "You're going to erase that time - the branch where he doesn't have it, anyway", as in "well, at least that branch", and exploiting that to mean that it's a branch on a branch that Steve is erasing, the branch from 2013 still existing. But that's clearly not the intention, the intention is that Steve is erasing the 2013 branch after returning Mjolnir.
 * Jeff Goldsmith: "Did you map out where Loki goes after he grabs the Tesseract in 2012?"
 * Stephen McFeely: "TBD."
 * Christopher Markus: "Probably to cause some havoc in Asgard."
 * Stephen McFeely: "It's probably mischief."
 * Jeff Goldsmith: "But if he has escaped a branched timeline before it was destroyed, would that inspire a new movie that reconciles what Loki does with the Tesseract?"
 * Stephen McFeely: "Listen, we don't work at Marvel, man. I don't know."
 * Goldsmith takes the branch being "destroyed" as a given from their conversation and McFeely does not refute this. It certainly seems that that is the writers' intention. Obviously, the show Loki is now happening following this Loki, but it would seem from McFeely that, by their time travel rules intention, Loki would have to escape that timeline before it is destroyed for the character to continue.
 * McFeely reiterates that they are not involved with Marvel's future so do not necessarily have the final world on the canon that will be established.

Quote

 * Melinda May: "O-Okay, so, so you're saying that, when Coulson went in there with it..."
 * Leo Fitz: "It's possible that the three energies combined to create another Coulson through space and time... on some other planet, years ago. And - and he was left there when our Coulson sealed the gravitonium device."

Dissecting

 * Melinda May: "O-Okay, so, so you're saying that, when Coulson went in there with it..."
 * Leo Fitz: "It's possible that the three energies combined to create another Coulson through space and time... on some other planet, years ago. And - and he was left there when our Coulson sealed the gravitonium device."
 * Again, the White Monolith purely transports you across time. Creation monolith: created Sarge, space monolith: at another point in space, time monolith (White Monolith): at another point in time. If the White Monolith operated by sending you to another universe at another point in time, Sarge would be that universe's problem. But he's in their universe, he was purely created at another point in time. The White Monolith purely sends you through time, not universes.

July 20, 2019: San Diego Comic-Con 2019 - Time Travel in the Quantum Realm Panel (Christopher Markus, Clifford V. Johnson, Kim Griest, Eric Michelsen, and Elizabeth Simmons Q&A)
https://www.youtube.com/watch?v=k0uxux4VDxk 7:13, 14:43, 16:50, 23:30, 30:17, 31:39, 35:29, 46:51

Quote
[...] [...] [...] [...] [...] [...] [...]
 * Christopher Markus: "It also, if you follow the Back to the Future rules, made solving the problem really pretty easy. Like you go back, just pluck one little stone out, stick it in your pocket - it never happened. And it encumbered upon us with thirty superheroes, and this many millions of dollars at stake, to make it a little more challenging. So, those rules did not work for us. And, so we had to rejigger them and luckily we have the Infinity Stones which seem to have their own rules, and so why didn't we just [...] lay some time travel rules on them, so we, as the Ancient One said, made it that you only create these branch realities when you remove an Infinity Stone from that time. So we could tighten up the possibilities. Because writing is all about just winnowing down the possibilities, the worst moment in any project is when you have too many options. And so, ideally, as time goes on, you're killing off options to get to one story. Which is why, people get exci- when people get excited about the multiverse, I just stare at them like, "Wha-? You can'- your stakes are gone!", like if, "Well, 1 inch over, there's a room where this didn't happen," it's like, "Well then why are we telling this story?" You know, "Oh, your dog died? Let's go over there and get your other dog from...", you know. So while it, you know, may be a fascinating idea, it's pretty hard on drama. But the time travel, on the whole, was actually great for drama, it turned out."
 * Clifford V. Johnson: "One of the things that I remember asking, would it be possible, when we talked about time travel movies that - or other aspects of science fiction, that I think really works well, is trying to lay in things where you can see that the consequences of the time travel were either implicitly or explicitly there all along, you just hadn't noticed it. And I think there are even aspects of that in the film as well. And..."
 * Christopher Markus: "Well it... We'll get to Captain America at the end of the movie..."
 * Clifford V. Johnson: "Right!"
 * Clifford laughs.
 * Christopher Markus: "... and whether that breaks all our own rules."
 * Clifford V. Johnson: "Right!"
 * Clifford laughs.
 * Clifford V. Johnson: "I have a way out for you on that..."
 * Christopher Markus: "Thank you."
 * Clifford V. Johnson: "... but we can get to that."
 * Audience member: "What are the rules?"
 * Christopher Markus: ""What are the rules?" So glad you asked that. In the movie, the rules are basically: If you - you can go back, you can do whatever you want, it won't affect the future. Unless you take out an Infinity Stone, then it branches. So, Steve only had to fix six... six paths. There weren't fifty-five million paths because of every encounter that they had. So that - so that we could do things like have Captain America fight himself without that creating, you know, a cosmic problem as opposed to a physical problem between two people. And I would like to believe, through some sort of... (bulls**t) "time loop... paradox" - I gotta throw in the words that you use when you're bulls**tting science in a movie - some sort of "quantum paradox", that there are indeed two Captain Americas in the MCU timeline, and that Steve Rogers who looped back into time has therefore always been there, and that he is living somewhere else in the movies you're watching, and what I'd really like to believe is that there's an old man sitting in back at Peggy's funeral in Civil War and that's old Steve Rogers watching young Steve Rogers carry old Steve Rogers' wife up to the front of the church. Can I explain it scientifically? Not really."
 * Eric Michelsen: "Deutsch is a believer in the "multi-worlds" interpretation of quantum mechanics which says that the universe is actually splitting into, sort of, very-similar-but-not-quite-exactly-the-same duplicate parallel universes, and in that model with certain ideas from quantum mechanics, what you'd find is that energy is conserved on average over all the universes, but not specifically and individually in every universe."
 * Clifford V. Johnson: Yeah, and you could argue instead of using multiverses, which perhaps is unsettling to some, it's our universe that's kind of being resewn in different - restitched in different ways, the narrative, you know, gets adjusted, but then you can go back at those insertion points and fix it."
 * Steve Snyder: "Let's talk about the Cap'n..."
 * Christopher Markus: "Yes."
 * Steve Snyder: "... and the return at the end. And how that related, in terms of, from a science point-of-view."
 * Christopher Markus: "Well what - I mean, we actually have a public disagreement..."
 * Clifford laughs.
 * Christopher Markus: "... with, with our directors. And, you know, it's a playful one, but we are just, Steve [McFeely] and I are just so taken with the idea that Steve [Rogers] went back and somehow therefore has always been back, and got to live his life. Because I mean, you get Captain America loyalists who say that if Cap goes back in time he is honor-bound to fix everything he knows is going to happen, so he has to go and save Bucky, he has to prevent the Kennedy assassination, he's a very busy man. But that's not why we sent him back. We sent him back so that he can become a whole person and finally come home from a war. So, we didn't want him to go back and just keep adventuring, we wanted him to rest, and the only way we could come to that solution is if there are two Caps, which I'm okay with. Some people - Anthony Russo yesterday proposed that he went out to the ice, got his frozen self, defrosted himself, and they have like a time share [...] also a valid theory, as far as I'm concerned."
 * Kim Griest: "Well, you know, the multi-world interpretation of time travel which you guys are using, you always have those two things."
 * Christopher Markus: "Yeah."
 * Kim Griest: "The Caps are there, and the David Deutsch solution is there's two Caps forever, just like you said, that would be the way that that would do."
 * Clifford V. Johnson: "If time travel to the past is possible, it might be in some limited way that somehow makes sure that all narratives make sense. And that's what I think's gonna be the way out, for..."
 * Kim Griest: "That's super cool, that's kind of like Hawking's "chronology protection"..."
 * Clifford V. Johnson: "Yeah."
 * Kim Griest: "... conjecture..."
 * Clifford V. Johnson: "So..."
 * Kim Griest: "... but..."
 * Clifford V. Johnson: "... it'll be..."
 * Kim Griest: "... it's a..."
 * Clifford V. Johnson: "... like..."
 * Kim Griest: "... little..."
 * Clifford V. Johnson: "... "narra-"..."
 * Kim Griest: "... weaker."
 * Clifford V. Johnson: "It'll be the "narrative protection conjecture"."
 * Kim Griest: "Interesting!"
 * Clifford V. Johnson: "You heard it here first, folks. Right? And so, it might be that from some person's point-of-view I made a time machine and I did a thing, from everyone else's point-of-view, you won't even notice that time travel has happened because you're just moving toward your future, even though from some perspectives, it's kind of went around and went to someone else's past. And I think there may be logical ways that the unive- - you know, it might be, you, you know - going back to H. G. Wells, right? You make the time machine, you go back in time, and then every time you try and do something that would stop you from making that time machine that would've sent you back, something happens: you trip over a wire, you, you know, an earthquake happens, and the universe somehow just, the physics propagates in such a way as to protect the narrative in some sensible way."
 * Clifford V. Johnson: "I actually do like examples of stories where you, as long as you never know where the loop is first entered, it's a perfect loop that sits in the story, and it's always there and it would, I think it's an example of..."
 * Kim Griest: "... of "narrative protection"?"
 * Clifford V. Johnson: "Well it's "narrative protection", but I think it's an example of a perfect closed time loop in physics that, that somehow, you know, that has some way of dissipating the buildup that you would get."
 * Kim Griest: "Yeah, and that's exactly what Deutsch does, but it does require non-unitary quantum mechanics unless you're doing something weird on the Planck scale."

Dissecting

 * Christopher Markus: "It also, if you follow the Back to the Future rules, made solving the problem really pretty easy. Like you go back, just pluck one little stone out, stick it in your pocket - it never happened. And it encumbered upon us with thirty superheroes, and this many millions of dollars at stake, to make it a little more challenging. So, those rules did not work for us."
 * Standard "It's not like Back to the Future" discussion.
 * Christopher Markus: "And, so we had to rejigger them and luckily we have the Infinity Stones which seem to have their own rules, and so why didn't we just [...] lay some time travel rules on them, so we, as the Ancient One said, made it that you only create these branch realities when you remove an Infinity Stone from that time."
 * Markus says that the time travel rules are laid on the Infinity Stones, and then specifically that "you only create these branch realities when you remove an Infinity Stone from that time", very explicitly laying out that point-of-view, as well as confirming that's what the Ancient One was saying when they wrote it.
 * Christopher Markus: "So we could tighten up the possibilities. Because writing is all about just winnowing down the possibilities, the worst moment in any project is when you have too many options. And so, ideally, as time goes on, you're killing off options to get to one story. Which is why, people get exci- when people get excited about the multiverse, I just stare at them like, "Wha-? You can'- your stakes are gone!", like if, "Well, 1 inch over, there's a room where this didn't happen," it's like, "Well then why are we telling this story?" You know, "Oh, your dog died? Let's go over there and get your other dog from...", you know. So while it, you know, may be a fascinating idea, it's pretty hard on drama. But the time travel, on the whole, was actually great for drama, it turned out."
 * Markus again implies that they did not want to be creating a multiverse with this, though it is unclear in what way they intended to avoid this - it's possible they're referring to timelines not being equivalent to universes.
 * Markus implying they did not want to be creating a multiverse could refer to the erasing of the timelines.
 * Clifford V. Johnson: "One of the things that I remember asking, would it be possible, when we talked about time travel movies that - or other aspects of science fiction, that I think really works well, is trying to lay in things where you can see that the consequences of the time travel were either implicitly or explicitly there all along, you just hadn't noticed it. And I think there are even aspects of that in the film as well. And..."
 * Christopher Markus: "Well it... We'll get to Captain America at the end of the movie..."
 * Clifford V. Johnson: "Right!"
 * Clifford implies he has seen Captain America's situation as the writers making it so that details that have always been in the films now have a significance as showing that time travel always happened, i.e. a time loop.
 * Clifford laughs.
 * Christopher Markus: "... and whether that breaks all our own rules."
 * Clifford V. Johnson: "Right!"
 * Clifford laughs.
 * Clifford V. Johnson: "I have a way out for you on that..."
 * Christopher Markus: "Thank you."
 * Clifford V. Johnson: "... but we can get to that."
 * They joke again about the Captain America debate.
 * Audience member: "What are the rules?"
 * Christopher Markus: ""What are the rules?" So glad you asked that. In the movie, the rules are basically: If you - you can go back, you can do whatever you want, it won't affect the future. Unless you take out an Infinity Stone, then it branches."
 * Markus refers again to nothing affecting time unless you remove an Infinity Stone.
 * The wording "you can do whatever you want" is a little odd, as it suggests you are not bound by time, yet you're not creating a branch timeline. So you should just be stuck in the normal timeline. So does he in fact mean that "you can try to do whatever but you won't manage to change things"? Or might he in some way mean that you are free to do whatever you want, it won't stick as an actual part of the timeline unless a branch is created by removing Infinity Stones? That's a potential new concept. It doesn't seem to fit either Steve explanation, however, as it would leave him living in essentially a non-existent space.
 * This comment seems to confirm that the intention of the Hulk statement was not to discuss branching timelines, just that you can't change the timeline, with the Ancient One statement then being the part about branches.
 * Christopher Markus: "So, Steve only had to fix six... six paths."
 * Steve would be fixing six rather than six branches - just because the timeline's split already when the Power Stone or Time Stone are removed from the main timeline, shouldn't mean it doesn't split again when the Soul Stone and Mind Stone are removed respectively. So you would have, by this interpretation, four branches off the main timeline, and two of those branches would have a further branch several minutes later off of them.
 * A problem with this is the same as one of the ones previously discussed about the idea that arriving through time also splits the timeline. The removal of an Infinity Stone theoretically should indeed be somehow solidifying everything since arrival as a splinter timeline. In 2012 and 2014, you are already in an alternate timeline, definitely by this point because the Time and Power Stones are already gone. If the further removal of an Infinity Stone were to cause a further split, you would end up with Scott Lang and Clint Barton being present in that time, and then a split when they go back leaving a timeline without an Infinity Stone, and a timeline still with it. And again: except, how? The Avengers going back is what removes the stone from the timeline, so you would have to have the split occur, say, the moment they hit the button to return, so in one version of events they disappear and in one they do not. So, why? Does it just not work? Why wouldn't it? And in that case, you also end up with versions of Scott and Clint abandoned in time. This is not as problematic a notion as with the idea of arrival causing a split, because there you would be looking at - if timelines are erased - the other timeline being erased and not the one where they are stranded, though in this case both would be erased, if the timelines are erased, so that's less of a problem. Still though, it's a little bizarre. You could question whether perhaps, because it's not actually said that it would be one timeline with stones and one without, maybe both timelines are missing a stone. That solves your stranded Avengers problem, except it is shown that removing an Infinity Stone creates one dark branch of reality specifically dark because it's missing an Infinity Stone, not that it poisons both timelines. Now, in this branch-on-a-branch situation, both would be missing Infinity Stones anyway, but it still implies that the way removing an Infinity Stone works is that you have one timeline with as many as before and one offshoot with minus one. That said, this is a different scenario to the one that Smart Hulk and the Ancient One are discussing, which is an initial removal from a complete set, one which it seems quite possibly makes everything since arrival an alternate timeline, so then just removing another one could function slightly differently, just further splitting the flow of time indiscriminately. After all, if the removal of an initial stone makes everything sine arrival an alternate timeline - which this point otherwise suggests, as discussed above - then you do have a problem: that would mean the further removal of an Infinity Stone theoretically would make no further difference, yet also it seems that removing another Infinity Stone would further break the flow of time. The idea of it just splitting further, not particularly where one result has more Infinity Stones than the other, serves as a compromise. So, this point would suggest that the initial removal of an Infinity Stone makes everything since arrival an alternate timeline, as previously discussed, and then is not necessarily a big problem with the idea of further splits in 2012 and 2014.
 * The implication is that there are six paths in total, each of which Steve is fixing in whatever manner - not that Steve is only fixing six of the paths. However, there is wiggle room in the statement for that to be the case if necessary.
 * Christopher Markus: "There weren't fifty-five million paths because of every encounter that they had. So that - so that we could do things like have Captain America fight himself without that creating, you know, a cosmic problem as opposed to a physical problem between two people."
 * They wanted it to be so that you can't change time, and the branches are clean splits, so each individual encounter isn't a problem. This doesn't, however, clear up whether he is referring to the idea that the timeline's already split (so no worries about where it goes), or if this is in line with the new concept his previous comment might have implied: that whatever you do in going back will just not stick as a part of the timeline (only having an impact if it's in an alternate timeline because you removed an Infinity Stone). Again, not clear if he meant it that way.
 * Christopher Markus: "And I would like to believe, through some sort of... (bulls**t) "time loop... paradox" - I gotta throw in the words that you use when you're bulls**tting science in a movie - some sort of "quantum paradox", that there are indeed two Captain Americas in the MCU timeline, and that Steve Rogers who looped back into time has therefore always been there, and that he is living somewhere else in the movies you're watching, and what I'd really like to believe is that there's an old man sitting in back at Peggy's funeral in Civil War and that's old Steve Rogers watching young Steve Rogers carry old Steve Rogers' wife up to the front of the church. Can I explain it scientifically? Not really."
 * Markus states his desire for this to be a time loop with Steve, always being in the main MCU timeline. He says it following on from explaining the rules about Infinity Stones, potentially implying that it's because of that. He's then just saying that he would like to think that a time loop makes sense.
 * Eric Michelsen: "Deutsch is a believer in the "multi-worlds" interpretation of quantum mechanics which says that the universe is actually splitting into, sort of, very-similar-but-not-quite-exactly-the-same duplicate parallel universes, and in that model with certain ideas from quantum mechanics, what you'd find is that energy is conserved on average over all the universes, but not specifically and individually in every universe."
 * This suggests that when Tony talks about triggering the Deutsch proposition, he is referring to split universes.
 * Clifford V. Johnson: Yeah, and you could argue instead of using multiverses, which perhaps is unsettling to some, it's our universe that's kind of being resewn in different - restitched in different ways, the narrative, you know, gets adjusted, but then you can go back at those insertion points and fix it."
 * An interesting way of putting it, from a science adviser to the film, which would align with Markus' comments about not wanting a multiverse to be involved.
 * Steve Snyder: "Let's talk about the Cap'n..."
 * Christopher Markus: "Yes."
 * Steve Snyder: "... and the return at the end. And how that related, in terms of, from a science point-of-view."
 * Christopher Markus: "Well what - I mean, we actually have a public disagreement..."
 * Clifford laughs.
 * Christopher Markus: "... with, with our directors. And, you know, it's a playful one...
 * Again joking about the disagreement.
 * Christopher Markus: "... but we are just, Steve [McFeely] and I are just so taken with the idea that Steve [Rogers] went back and somehow therefore has always been back, and got to live his life."
 * The writers really like this idea. Again, not necessarily saying this is the absolute canon, but certainly what they intended with the ending.
 * Christopher Markus: "Because I mean, you get Captain America loyalists who say that if Cap goes back in time he is honor-bound to fix everything he knows is going to happen, so he has to go and save Bucky, he has to prevent the Kennedy assassination, he's a very busy man."
 * Markus here addresses a criticism some fans have raised with the idea of Steve being in the same timeline. It is a false criticism, however, as a time loop does not allow for changing time - by the writers' interpretation that only removing an Infinity Stone causes a split in the timeline, Steve would have no option of changing events. He would just be a part of the MCU timeline that always was this way and so always is this way. Markus does not address that part of the response to this criticism here, though, but that comes up later.
 * Christopher Markus: "But that's not why we sent him back. We sent him back so that he can become a whole person and finally come home from a war. So, we didn't want him to go back and just keep adventuring, we wanted him to rest, and the only way we could come to that solution is if there are two Caps, which I'm okay with.
 * So, as well as the discussion later of how it simply is not necessarily valid anyway, the writers also have intended that Steve would not be trying to save everyone and change everything anyway.
 * Christopher Markus: "Some people - Anthony Russo yesterday proposed that he went out to the ice, got his frozen self, defrosted himself, and they have like a time share [...] also a valid theory, as far as I'm concerned."
 * Markus addresses the Russos' different theory.
 * Kim Griest: "Well, you know, the multi-world interpretation of time travel which you guys are using, you always have those two things."
 * It's not clear if Griest has understood what Markus is saying, since this part of the discussion is not about multiple worlds.
 * Christopher Markus: "Yeah."
 * Kim Griest: "The Caps are there, and the David Deutsch solution is there's two Caps forever, just like you said, that would be the way that that would do."
 * If Griest has understood, then he is saying that the science would support Markus' theory, but it's not clear if he has.
 * Clifford V. Johnson: "If time travel to the past is possible, it might be in some limited way that somehow makes sure that all narratives make sense. And that's what I think's gonna be the way out, for..."
 * Clifford is referring back to what he said earlier, that he had an explanation for Captain America to make it work. So this is that explanation.
 * Kim Griest: "That's super cool, that's kind of like Hawking's "chronology protection"..."
 * Clifford V. Johnson: "Yeah."
 * Kim Griest: "... conjecture..."
 * Clifford V. Johnson: "So..."
 * Kim Griest: "... but..."
 * Clifford V. Johnson: "... it'll be..."
 * Kim Griest: "... it's a..."
 * Clifford V. Johnson: "... like..."
 * Kim Griest: "... little..."
 * Clifford V. Johnson: "... "narra-"..."
 * Kim Griest: "... weaker."
 * Clifford V. Johnson: "It'll be the "narrative protection conjecture"."
 * Kim Griest: "Interesting!"
 * Clifford V. Johnson: "You heard it here first, folks. Right? And so, it might be that from some person's point-of-view I made a time machine and I did a thing, from everyone else's point-of-view, you won't even notice that time travel has happened because you're just moving toward your future, even though from some perspectives, it's kind of went around and went to someone else's past."
 * Here, Clifford, a science adviser to the film, discusses a version of time travel, to do with time loops, where you do not actually affect time per se, you're just in the timeline. The time-traveller's perspective is the only thing that has shifted.
 * Clifford V. Johnson: "And I think there may be logical ways that the unive- - you know, it might be, you, you know - going back to H. G. Wells, right? You make the time machine, you go back in time, and then every time you try and do something that would stop you from making that time machine that would've sent you back, something happens: you trip over a wire, you, you know, an earthquake happens, and the universe somehow just, the physics propagates in such a way as to protect the narrative in some sensible way."
 * 'Clifford is therefore saying that he feels the way out for the Steve situation is that he simply went back in the timeline and lived through it again, and had no choice to change anything. This is how time loops would work, you are simply in the timeline, things would happen the way they always did because they are the things that always did happen, it's the same events. Not identical events, literally the same ones. And if you like, it can be seen as the universe/timeline protecting itself, protecting its narrative, as Clifford puts it here. Steve could try to change things, but every time he does, he will just trip over a wire, be caught in an earthquake, etc., no matter how unlikely. And if, at any point in the MCU films, people had looked up earthquakes that happened in the past, there always would have been one on the date Steve then experiences one on in the past. Because it's the same timeline. No matter how unlikely, if Steve were to keep trying he would always be caught in those earthquakes or whatever other incidents that prevent him, because he can't succeed, because he didn't succeed, because time played out this way. This explains why the argument that Steve should have stopped certain events from happening is not applicable - it's not how the science of the time loop would likely work, as Clifford V. Johnson here explains. This is similar to Simmons' invincibility tests in Marvel's Agents of S.H.I.E.L.D.: Season 5. She goes through stunts where she should almost certainly die, yet is confident that she won't, because she can't, because she knows she survives into at least the 2020s. And she doesn't die despite the odds, because, from a certain perspective, the timeline is protecting her. She doesn't die in 2018-2022 because she doesn't die until post-2022, she doesn't die until post-2022 because she doesn't die in 2018-2022, she doesn't die in 2018-2022 because she doesn't die until post-2022, etc.. Steve doesn't successfully (if he even tried) save Bucky from Hydra in 1948-2014 because Bucky doesn't escape Hydra until 2014, Bucky doesn't escape Hydra until 2014 because Steve doesn't successfully save him from Hydra in 1948-2014, Steve doesn't successfully save Bucky from Hydra in 1948-2014 because he doesn't escape Hydra until 2014, etc.. And, because of this, it would be useless for Steve to try. He might as well rest, and in combination with the writers' comments, I believe from all of this that it can be concluded that he rested, knowing there is nothing that can be done, but that the world will be overall okay by 2023 anyway, and now he can just rest with Peggy. It's essentially like Steve has just been transported into a cinema, with Peggy, to watch the MCU films play out and spend time together while they do it.'
 * Imagine it like this: Someone who has seen the near future sits you down and puts a pencil in front of you, and they tell you they know with 100% certainty, having seen it, that you will not pick up the pencil. You could think, "Oh, really? Well what if I just... do." And you go to pick it up, but then think, "But apparently I don't. I wonder why that is?", and pause. But, "No, why not? I'll just do it, I'm curious. Why shouldn't I?" And then you try, and pause again, "But what if they're playing mind games with me? I mean, why would I pick up the pencil otherwise, if I hadn't specifically been told I don't? Why should I? No, I just won't." And then you decide not to. But then you think, "But now I'm just playing directly into this supposed future of not picking it up, it's all happening because of this thought. I'm overthinking it, I'll just pick up the pencil. But I'm still reconsidering. And I guess I don't pick it up because I'm reconsidering, so the fact that I'm thinking this is the reason I don't pick it up, which is the reason I then get told about it and end up thinking like this." Whatever happens, you're not going to manage to pick up the pencil. You might even just go for it, but then there will be an earthquake or something similar, you never pick up that pencil. The earthquake didn't happen to prevent you picking up the pencil. It just happened, and prevented you from picking up the pencil. And the person who spoke to you then saw that, so could tell you that they knew you wouldn't manage to pick it up. This is the situation Steve would find himself in. He essentially has been told that he will not successfully rescue Bucky or stop assassinations, or whatever else, because he has lived through that history. So whatever he tries, it cannot affect anything, because time is just playing out. Events will play out the same because they are literally the same events just being experienced again.
 * Clifford V. Johnson: "I actually do like examples of stories where you, as long as you never know where the loop is first entered, it's a perfect loop that sits in the story, and it's always there and it would, I think it's an example of..."
 * Kim Griest: "... of "narrative protection"?"
 * Clifford V. Johnson: "Well it's "narrative protection", but I think it's an example of a perfect closed time loop in physics that, that somehow, you know, that has some way of dissipating the buildup that you would get."
 * Science adviser Clifford V. Johnson expresses his partiality to the idea of the closed time loop simply sitting in time, mitigating physics problems.
 * Kim Griest: "Yeah, and that's exactly what Deutsch does, but it does require non-unitary quantum mechanics unless you're doing something weird on the Planck scale."
 * Griest seems to imply here that while Deutsch was earlier mentioned to have discussed multi-worlds, he also makes conclusions about time loops. He also says that it requires either non-unitary quantum mechanics or something weird on the Planck scale. Tony specifically says "quantum fluctuation messes with the Planck scale, which then triggers the Deutsch proposition", so this would suggest that because they're messing with the Planck scale, the Deutsch proposition is triggered, which Griest's comments would suggest is the idea of time loops.

July 20, 2019: IGN - Russos Interview
https://za.ign.com/marvels-the-avengers-4/134902/news/russos-say-captain-america-certainly-met-red-skull-in-avengers-endgame

Quote
[...]
 * Joe Russo: "He would have certainly met Red Skull to return the stone."
 * Anthony Russo: "Part of the beauty of this issue is that really that's what it comes down to in the writers room when we collaborate together. We talk about all the infinite possibilities, we talk about all the different interpretations and versions, but at the end of the day, and this is true for the entire MCU, there are many more possibilities that are discussed that then make their way into the movies themselves. So the text becomes the movie, and then you use that text in the film as a jumping off point for future storytelling."
 * Joe Russo: "It's not defined specifically in [Endgame], it'll be defined by a future movie. Of course, we give rules. I think the rules are also open to debate, clearly. Our interpretation of that is a multiverse, which we just think is a lot of story potential. But we're not really at Marvel anymore, so this is a Kevin problem."

Dissecting

 * Joe Russo: "He would have certainly met Red Skull to return the stone."
 * Again, meaning Steve would have to physically return the stones to each place.
 * Anthony Russo: "Part of the beauty of this issue is that really that's what it comes down to in the writers room when we collaborate together. We talk about all the infinite possibilities, we talk about all the different interpretations and versions, but at the end of the day, and this is true for the entire MCU, there are many more possibilities that are discussed that then make their way into the movies themselves. So the text becomes the movie, and then you use that text in the film as a jumping off point for future storytelling."
 * Joe Russo: "It's not defined specifically in [Endgame], it'll be defined by a future movie. Of course, we give rules. I think the rules are also open to debate, clearly."
 * Joe acknowledges the difference in opinion between them and Markus and McFeely, and states, like the writers, that nothing is set in stone yet and it's open to debate.
 * Joe Russo: "Our interpretation of that is a multiverse, which we just think is a lot of story potential."
 * Joe talking about the multiverse here possibly touches on a wider debate rather than just Captain America's ending, as the "multiverse" is not really the direct answer to the Cap question. So, either Joe simply means, "Our interpretation is that the answer to Cap's situation relates to the multiverse, being another universe," or he's referring to a larger point, "Our interpretation of the time travel rules is that it creates a multiverse." It appears to be the latter, as it follows on from Joe talking about the rules in the film, rather than the general point he's making about there being a disagreement over Captain America. This also implies that there is an interpretation where it is not the multiverse that's involved, lining up with the implication from the writers talking about how they didn't want a multiverse.
 * This implies that the timelines are still around as part of the universe.
 * Joe Russo: "But we're not really at Marvel anymore, so this is a Kevin problem."
 * Like the writers, the Russos admit they are not involved with Marvel's future.

July 30, 2019: Avengers Endgame Digital Release - Commentary Track (Russos and Markus and McFeely Commentary)
https://filmschoolrejects.com/avengers-endgame-commentary/ https://comicbook.com/marvel/2019/08/01/avengers-endgame-directors-and-writers-address-if-captain-americ/

Quote

 * Film School Rejects: ""Have you guys thought about whether or not Cap runs into Red Skull when he's returning the Soul Stone?" At this point the two writers seem to disagree as to whether Red Skull has been released from his bonds and therefore not there anymore. If there's no Soul Stone, there's no guardian right?"
 * Comic Book: "Co-director Anthony Russo brought it up first, asking the writers Christopher Markus and Stephen McFeely whether they had considered the idea. "He would have to," McFeely said, and Markus added that he had considered the question "many times". The pair speculated that just because the Soul Stone was gone, does not mean the Skull would have been freed from his obligation to guard its location. It might, Markus reasoned, come back. McFeely seems slightly less sure, wondering what he would be doing, just trapped there and waiting for something that might never happen, but before the argument could get too involved, Russo concluded, "It's fun to think about," and the commentary moved on."

Dissecting

 * Film School Rejects: ""Have you guys thought about whether or not Cap runs into Red Skull when he's returning the Soul Stone?" At this point the two writers seem to disagree as to whether Red Skull has been released from his bonds and therefore not there anymore. If there's no Soul Stone, there's no guardian right?"
 * Comic Book: "Co-director Anthony Russo brought it up first, asking the writers Christopher Markus and Stephen McFeely whether they had considered the idea. "He would have to," McFeely said, and Markus added that he had considered the question "many times". The pair speculated that just because the Soul Stone was gone, does not mean the Skull would have been freed from his obligation to guard its location. It might, Markus reasoned, come back. McFeely seems slightly less sure, wondering what he would be doing, just trapped there and waiting for something that might never happen, but before the argument could get too involved, Russo concluded, "It's fun to think about," and the commentary moved on."
 * The debate here seems to be more focused on whether Red Skull has been released from his bonds or not. The implication is that Steve having to physically return the stones is a given.

August 7 2019: Reddit - Russos AMA
https://www.reddit.com/r/marvelstudios/comments/cn9lbx/were_joe_and_anthony_russo_directors_of_marvel/ew9238h/?context=8&depth=9 https://www.reddit.com/r/marvelstudios/comments/cn9lbx/were_joe_and_anthony_russo_directors_of_marvel/ew93msq/?context=8&depth=9

Quote
[...]
 * u/Reggie_48: "Can you help me/everyone understand how Captain America got back to the main timeline when he returned all the stones, because it contradicts the time travel theory stated by Banner earlier in the movie. Banner said that when you go back in time you make a separate timeline, so it doesn't [affect] the past, but if Captain America was in a different timeline when he returned the stones, how did he [get] back to the main timeline without the use of the quantum suits[?]"
 * Russo brothers: "You are correct in that he would have had to have worn the quantum suit, using a Pym particle to make the jump. He's not wearing the suit on the bench, because that is not the exact moment to which he returned."
 * u/Nirok: u/Nirok: "How did the meeting between Cap and the Red Skull go when he returned the Soul Stone after [Avengers: ] Endgame? Is there a story there and will we ever see it in a future movie?"
 * Anthony Russo: "It was probably more awkward than you imagine it was. Red Skull felt slated because Cap didn't recognize him."

Dissecting

 * u/Reggie_48: "Can you help me/everyone understand how Captain America got back to the main timeline when he returned all the stones, because it contradicts the time travel theory stated by Banner earlier in the movie. Banner said that when you go back in time you make a separate timeline, so it doesn't [affect] the past, but if Captain America was in a different timeline when he returned the stones, how did he [get] back to the main timeline without the use of the quantum suits[?]"
 * I've corrected the spelling and grammar through this message to make it easier to read.
 * This user incorrectly states what Banner says. Banner never said that if you go back in time you make a separate timeline. He said you can't change the past, and that if you are in the already process of changing past events then you're still not changing the past. The implication of his statement is then that either it's just not possible to change past events, or that if it is, you would be in an alternate timeline, he doesn't specify. But either way, it's only if you are changing things, and not just jumping back in time.
 * The question is poorly phrased, anyway. I assume he means "Banner establishes that you make a new timeline" (incorrect) "so Captain America would have to have created a new timeline, which would mean he has to get back to the main timeline. But Steve isn't wearing the Quantum Realm suit, so he can't have gone to another timeline - except he has to have, so there's a contradiction here. Can you explain?"
 * The user is asking a fairly irrelevant question, as the Quantum Realm suits have been shown to just fold up instantaneously. A better question would be how Steve does not come out of the Quantum Tunnel there and then.
 * Russo brothers: "You are correct in that he would have had to have worn the quantum suit, using a Pym particle to make the jump."
 * The Russos seem to implicitly suggest it's correct that if you go back in time, you make a separate timeline.
 * The Russos again say that Steve would have made specifically a Pym particle jump. When they were mysterious about the method of Steve's return, it made more sense, because the problem was that he seemingly couldn't have used a Pym particle to return to the main timeline without coming out through the Quantum Tunnel there and then. But if he did, then that raises that problem again.
 * Russo brothers: "He's not wearing the suit on the bench, because that is not the exact moment to which he returned."
 * Despite the user not asking the more pertinent question of how Steve could have returned without coming through the Quantum Tunnel, the Russos have addressed it here, saying he did, just he came out at another time. It's not clear, however, how this would be possible, with the Avengers through the film simply hitting a return button and coming out at the programmed time a few seconds after they left, and no precedent for otherwise programming your return timeline, date, and time the way Steve would've had to here. It is also not clear how Steve could have sneaked out of the Quantum Tunnel at some previous time, implying that a) the new Quantum Tunnel has not only just been finished, for some reason they waited to return the stones, b) it was left unattended at some point, and c) that Steve knew a point when it was unattended to have programmed himself to come out of the Quantum Tunnel.
 * This puts paid to the argument that Steve must have come from an alternate timeline specifically because he "only just appeared on that bench, he didn't hide and then go and sit on it."
 * u/Nirok: "How did the meeting between Cap and the Red Skull go when he returned the Soul Stone after [Avengers: ] Endgame? Is there a story there and will we ever see it in a future movie?"
 * Anthony Russo: "It was probably more awkward than you imagine it was. Red Skull felt slated because Cap didn't recognize him."
 * Again, a comment that Steve had to physically go and meet Red Skull to return the Soul Stone.

August 19, 2019: Canada.com - Markus and McFeely Interview
https://beta.canada.com/entertainment/movies/we-considered-ways-to-let-tony-live-avengers-endgame-writers-on-decision-to-kill-iron-man/wcm/bd55e2a4-da98-408e-90ff-7896db44c436/amp/

Quote

 * Mark Daniell: "At the conclusion of Endgame, Captain America (Chris Evans) goes back to the past and lives his life with Peggy Carter (Hayley Atwell). But 2014's Winter Soldier established that Peggy had a husband and two kids. What does Steve going back in time do to that timeline?"
 * Stephen McFeely: "It depends on what story Marvel wants to tell going forward. I don't know if Marvel wants to tell any more Captain America stories or if Chris [Evans] is up for it. Do they want to tell an alternate timeline story? Chris [Markus] and I are partial to the idea that Steve is part of a strange, unique time loop where he has always been there. The husband that you very purposefully did not see at Peggy's bedside in Winter Soldier is Chris [Evans]' Steve. We have always thought that he was her husband. The movies you have been watching follow a line where he always goes back. To be fair, not everyone agrees with us. I don't even know if Marvel agrees with us. But that's what we think."

Dissecting

 * Mark Daniell: "At the conclusion of Endgame, Captain America (Chris Evans) goes back to the past and lives his life with Peggy Carter (Hayley Atwell). But 2014's Winter Soldier established that Peggy had a husband and two kids. What does Steve going back in time do to that timeline?"
 * Stephen McFeely: "It depends on what story Marvel wants to tell going forward. I don't know if Marvel wants to tell any more Captain America stories or if Chris [Evans] is up for it. Do they want to tell an alternate timeline story?"
 * McFeely again discusses how the final canon is up to Marvel.
 * Stephen McFeely: "Chris [Markus] and I are partial to the idea that Steve is part of a strange, unique time loop where he has always been there."
 * The writers discuss again how they feel it should be a time loop with Steve having always been there.
 * Stephen McFeely: "The husband that you very purposefully did not see at Peggy's bedside in Winter Soldier is Chris [Evans]' Steve. We have always thought that he was her husband."
 * McFeely makes it sound here more like it was always their intention to make it this way. It is possible that they intentionally left the husband out not just to leave options open but, by the sound of it, in the hope that they could find a way to make it so that Steve was always that husband. But this in particular makes it sound like this was the long game for the writers, very much establishing the idea of Steve being Peggy's husband and part of the main timeline as an intentional choice.
 * Stephen McFeely: "The movies you have been watching follow a line where he always goes back.
 * McFeely again explains the time loop, as some people are confused about how Steve "changing" time could not cause a new timeline. But by the writer explanation, Steve didn't "change" time, he merely travelled in time, as this is how time loops work. So he was always there, he was always part of everything we've seen, we just never knew it.
 * Stephen McFeely: "To be fair, not everyone agrees with us. I don't even know if Marvel agrees with us. But that's what we think."
 * Again, it's up to Marvel to establish the final canon.

August 19, 2019: WIRED - Russos Interview
https://www.youtube.com/watch?v=-7wgC0-xOZE&t=310s

Quote

 * @simplymarrisa: "Serious question: when [Doctor] Strange is seeing all the scenarios for how the war could end, does he see it like a montage or a movie? How do you as the creators see this happening in his brain[?]"
 * Anthony Russo: "This is a great question..."
 * Joe Russo: "Yeah..."
 * Anthony Russo: "... and it's..."
 * Joe Russo: "... it's cool."
 * Anthony Russo: "... I mean, Strange has to exert an immense amount of energy into goi- - to go into this state, and the amount of time that he's in this state, as we know from, from the history in his own standalone film, Doctor Strange, he could be in that, in that state for... who knows how long? So it could have taken Strange an immensely long time to actually review all these scenarios."
 * Joe Russo: "He has to physically live them..."
 * Anthony Russo: "Yeah."
 * Joe Russo: "... and then die in each of them, and right before he dies he has to reset it, as we saw at the end of Doctor Strange, and do it again - and take copious notes each time he does it."

Dissecting

 * @simplymarrisa: "Serious question: when [Doctor] Strange is seeing all the scenarios for how the war could end, does he see it like a montage or a movie? How do you as the creators see this happening in his brain[?]"
 * Anthony Russo: "This is a great question..."
 * Joe Russo: "Yeah..."
 * Anthony Russo: "... and it's..."
 * Joe Russo: "... it's cool."
 * Anthony Russo: "... I mean, Strange has to exert an immense amount of energy into goi- - to go into this state, and the amount of time that he's in this state, as we know from, from the history in his own standalone film, Doctor Strange, he could be in that, in that state for... who knows how long? So it could have taken Strange an immensely long time to actually review all these scenarios."
 * Joe Russo: "He has to physically live them..."
 * Anthony Russo: "Yeah."
 * Joe Russo: "... and then die in each of them, and right before he dies he has to reset it, as we saw at the end of Doctor Strange, and do it again - and take copious notes each time he does it."
 * While, in my opinion, this was not clear in Avengers: Infinity War, the Russos are explaining that what Strange is doing is essentially the same as his loop with Dormammu, trapping them in a time loop (not the big time travel type) where events then play out as normal, but are reset each time, returning to that moment on Titan, until he's done and breaks out of it, having to everyone else's point of view, not gone anywhere. He hasn't meddled with the timeline in any way, just gone around a tangential loop fourteen million, six hundred and five times that always resets to that point on Titan. This solves the problem of whether there are fourteen million, six hundred and four timelines out there where things turned out badly, of whether the films were just happening to follow the one timeline where things turned out well and the Avengers didn't actually particularly achieve saving things, of whether Strange would have been seeing millions of timelines in which he had already seen the millions of timelines. There's no multiple timeline stuff going on with Strange, it's just one of his Dormammu loops, and then the Avengers manage to make things happen similarly to the one outcome he saw in his loop where things turned out well.

September 11, 2019: WIRED - Jen Underdahl Interview
https://www.youtube.com/watch?v=BdHCp62jC84 5:22, 6:46

Quote
[...]
 * Jen Underdahl: "So in the case of Captain America, what would a super soldier look like if he had aged 106 years?"
 * Jen Underdahl: "We shrunk his shoulders and sort of his overall profile to give him that 106-year-old super soldier look."

Dissecting

 * Jen Underdahl: "So in the case of Captain America, what would a super soldier look like if he had aged 106 years?"
 * Steve was 9713 days old when he went into the ice, and lived a further 4406 days, roughly, from 2011 to 2023. This would make him approximately 14,119 days old when he went back, 38.656. This first comment would suggest one of four things. 1, that Steve is biologically 106 years old, having aged 106 years in his total lifetime. This would mean that approximately 67.844 years have passed for Steve. This would require him to return to 1955 if he were in the singular timeline, which does not work with that interpretation being said to have Steve going back to 1948 or Peggy getting married no later than 1953, unless she remarried and that was a different, previous husband. 2, that Steve has aged 106 years over his lifetime, however long that has been, potentially ageing slower. Compatible for whatever interpretation. 3, that Steve has aged 106 years since becoming a super soldier. 594 days passed between him becoming a super soldier and going into the ice, plus the 4406 days in the present, 4512 days/12.353 years. This would mean roughly 93.647 years to have passed for Steve. This would require him to return to 1930 going by the singular timeline interpretation, which cannot be the case. 4, that 106 years have passed for Steve since he left. This would require him to return to 1917 going by the singular timeline explanation, which cannot be the case.
 * Jen Underdahl: "We shrunk his shoulders and sort of his overall profile to give him that 106-year-old super soldier look."
 * This second comment would then suggest that they mean either 1 or 2. He's either 106 years old, or meant to have the "106-year-old super soldier look" and not necessarily be 106. Since "super soldier" is already an asterisk note in this comment, like she's saying, "He's supposed to have the look not necessarily of a normal 106-year-old, but a 106-year-old who was a super soldier so is still doing physically a little better than most", it seems to be number 1. Not that he's supposed to have an "106-year-old look" and happen to be a super soldier. Plus there's no evidence in the MCU of the super soldier serum slowing ageing. It's not clear how authoritative this comment is, if they were just told "Make him look about 106ish" or if it was a big, calculated number over with the Russos/Marvel, but still, all that said, this comment supports the alternate timeline interpretation, and would mean that Steve lived about 67.844 years in the alternate timeline.
 * As established, it's likely this means Steve is supposed to be 106, so lived about 67.844 years if in an alternate timeline. If Steve lived approximately 68 years in the alternate timeline, it would make sense for him to have come back when Peggy died (though not immediately after, considering he isn't grieving), presumably around the same time as the main timeline, mid-2016. This would mean that he likely arrived around 1948, suggesting that whatever interpretation of Steve's time travel is taken, 1948 is the year he goes back to.

Marvel's Agents of S.H.I.E.L.D. (in-universe, the characters might be mistaken)
Merely transports you through a gateway across time, not to another universe.
 * Deke Shaw: "When? What year?"
 * Phil Coulson: "That monolith was different, wasn't it? We didn't travel through space."
 * The unspoken line here is clearly, "We traveled through time." The first monolith purely functioned on transport through space, the White Monolith purely functions on transport through time. This would imply no different universe-shifting of any sort, purely shifting across time.
 * Merely transports you through a gateway across time, not to another universe.
 * Tess: "That's insane."
 * Melinda May: "Doesn't mean it's not true."
 * Jemma Simmons: "We came through a gateway, some sort of temporal shift."
 * This lays it out clearly as a gateway shifting you through time, and only that (if Simmons is correct, but this nonetheless communicates the writers' intent).
 * Merely transports you through a gateway across time, not to another universe.
 * Kasius: "Did you come through time together or separately?"
 * Kasius says they have come through time, not across to another universe (if Kasius is correct, but this nonetheless communicates the writers' intent).
 * Merely transports you through a gateway across time, not to another universe.
 * Kasius: "In fact, she also traveled through time with the Destroyer of Worlds."
 * Another comment about travelling through time, just time, nothing else (not universes).
 * Leo Fitz: "How many travelled in time with the Destroyer?"
 * Another comment about travelling through time, just time, nothing else (not universes).
 * Kasius: "You see, Ben was present when I asked the Destroyer if others had traveled through time with her."
 * Another comment about travelling through time, just time, nothing else (not universes).
 * Merely transports you through a gateway across time, not to another universe.
 * Jemma Simmons: "He needs medical attention. Story time can wait."
 * Alphonso Mackenzie: "Well, not when those stories include time travel."
 * Mack assumes Fitz time-travelled the way they did. Another comment about travelling through time, just time, nothing else (not universes).
 * Merely transports you through a gateway across time, not to another universe.
 * Samuel Voss: "She goes back in time, you already know what will happen."
 * Another comment about travelling through time, just time, nothing else (not universes).
 * Merely transports you through a gateway across time, not to another universe.
 * Kasius: "She who predicted they'd come through time."
 * Another comment about travelling through time, just time, nothing else (not universes).
 * Merely transports you through a gateway across time, not to another universe.
 * Flint: "Yeah, well, still don't know how I'm supposed to build a time machine."
 * Leo Fitz: "It's a portal, not a time machine."
 * I assume the reason Fitz makes this distinction is that it's essentially a portal, a gateway between two points, just two points in time, rather than two points in space. They are not actually travelling in/with the machine like a traditional "time machine".
 * Leaning toward that it merely transports you through a gateway across time, not to another universe.
 * Deke Shaw: "But none of the time-travelers can go, because you all need to be at the rendezvous when it's turned on, so do the math."
 * Another comment about travelling through time, just time, nothing else (not universes).
 * Merely transports you through a gateway across time, not to another universe.
 * Elena Rodriguez: "Why are we still in the Lighthouse?"
 * Alphonso Mackenzie: "Maybe Flint's monolith didn't work."
 * Melinda May: "So we find him, try again."
 * Leo Fitz: "No, it worked. It takes you through time, but to the same place."
 * This is a discussion again about how the White Monolith merely transports you through time. There is no parallel universe involved.
 * Merely transports you through a gateway across time, not to another universe.
 * Daisy Johnson: "You people literally kidnapped us and then took us to another time."
 * Another comment about travelling through time, just time, nothing else (not universes).
 * Merely transports you through a gateway across time, not to another universe.
 * Deke Shaw: "I lived in the Lighthouse my entire life, only to time travel into the past and still spend every single day of my life inside the freaking Lighthouse. So it's like, even without Kasius around, this place just has this leash that keeps pulling me back in."
 * Another comment about purely "time travel" and the past, it would seem that Deke does not believe he switched universes in his time travel.
 * Merely transports you through a gateway across time, not to another universe.

Marvel's Agents of S.H.I.E.L.D. (factual)
Merely transports you through a gateway across time, not to another universe.
 * Lance Hunter: "You don't seriously believe all this, do you? A prophecy and a monolith that sends you through time?"
 * The White Monolith is again said to send you "through time", purely time, the same way the previous monolith sent you purely through space.
 * Leo Fitz: "Send me through to them."
 * Enoch: "The stone can only be activated from the other end. I only knew when it would open. I have no knowledge of who opened it."
 * If the White Monolith opens a gateway through time and someone in 2091 opened a connection to 2017, there is no reason it would randomly connect to another universe's 2017. It would just connect to 2017. This again suggests that the White Monolith purely shifted them through time.
 * Merely transports you through a gateway across time, not to another universe.
 * Leo Fitz: "The shard fits into the machine right here."
 * Jemma Simmons: "Maybe that's how it was able to target the monolith across time. This could be our way home."
 * The White Monolith machine, when activated by the True Believers in 2091, targeted the same White Monolith "across time" (in 2017). That's all the White Monolith does, it just connects two points in time, the same way the other monolith connects two points in space. There is no way it could transport you into another universe. The 2091 is the 2091 of the same universe, the same timeline.
 * Merely transports you through a gateway across time, not to another universe.
 * Jemma Simmons: "This bit here, laser vibrometer. So, it, it measures the resonant frequencies of the monolith piece"
 * Leo Fitz: "And locks onto the frequencies in the monolith through space-time."
 * Again, the White Monolith locks onto another point in the space-time continuum. The universe's space-time continuum. There is no reason it should be able to lock to another point in another universe's space-time continuum.
 * Merely transports you through a gateway across time, not to another universe.
 * Deke Shaw: "So, one more time, the machine uses the little piece to trigger the bigger piece through space?"
 * Leo Fitz: "Yeah, or time."
 * Jemma Simmons: "It mirrors the harmonic resonant frequency of photons, which can exist out of space-time."
 * Another comment about triggering the piece in 2017 and linking across the space-time continuum, not a different universe or a different space-time continuum.
 * Merely transports you through a gateway across time, not to another universe.
 * Melinda May: "O-Okay, so, so you're saying that, when Coulson went in there with it..."
 * Leo Fitz: "It's possible that the three energies combined to create another Coulson through space and time... on some other planet, years ago. And - and he was left there when our Coulson sealed the gravitonium device."
 * Again, the White Monolith purely transports you across time. Creation monolith: created Sarge, space monolith: at another point in space, time monolith (White Monolith): at another point in time. If the White Monolith operated by sending you to another universe at another point in time, Sarge would be that universe's problem. But he's in their universe, he was purely created at another point in time. The White Monolith purely sends you through time, not universes.
 * Merely transports you through a gateway across time, nothing else.

Result
No debate: It merely transports you across time, nothing else.

Marvel's Agents of S.H.I.E.L.D. (in-universe, the characters might be mistaken)
Just seeing the future, not another universe's future.
 * Leo Fitz: "Her father was an Inhuman. Every time he touched someone, he and that person would have a vision of an impending death. And it must have been torturous. So he couldn't have any human contact. Not with his wife. Not with his, not his baby daughter."
 * Lance Hunter: "And they still call these "gifts"?"
 * Leo Fitz: "He saved Daisy. And she was convinced that she could save him, change the future, but -"
 * Lance Hunter: "What's written is written."
 * As shown in Spacetime, Charles Hinton's power involved seeing the future. Not another future, the future, that then played out. Robin has adopted a power in the same vein, minus the seeing a death part. With Robin seeing events from the near future through to 2091 throughout the season, and her power clearly being to see the future, that plays out, not a possible future or another universe's future, this would again mean that the 2091 we see play out is the future.
 * Polly Hinton: "Her mind has been scattered. Past, present, future it's all the same to her, all mixed up. Sometimes, she doesn't even know I'm her mother."
 * Again, Robin's mind is scattered across the timeline. She sees the past, the present, the future, it doesn't matter, it's all the same. Present isn't relevant, her mind just goes to different points on the timeline. Her mind numerous times goes to the 2091 the agents are involved in, so that's the same timeline's 2091.
 * Just seeing the future, not another universe's future.
 * Samuel Voss: "It's like her life is a deck of cards shuffled out of order. She's a seer, alright, but nowadays, she can't separate past, present, and future."
 * Again, Robin's powers mean her mind simply jumps around the timeline (like the film Arrival) to different points in her life, out of order. So, when we see Robin in 2017/2018 and she connects to/remembers moments from 2091, that must mean that the 2091 of the main universe is indeed dystopian. Even if, for some reason, the 2091 shown in the first half of the season were that of an alternate universe, that doesn't change the fact that the main universe's future is dystopian, and for it not to be they had to actually, in some capacity, change things - as will be got to later. The reason why some might argue for it being an alternate universe is for it to be that the main universe's timeline just has a nicer future, to link with the idea of not being able to change time - that they just prevented things from going down the same route in their universe. But clearly the future of their universe is dystopian (until they split the timeline) anyway, so the 2091 events from the first half of Season 5 might as well be, considering all the other evidence, the same universe's future and not another one's.
 * Phil Coulson: "She's the connection between the two points in time. This is our answer."
 * Melinda May: "The problem is, for her, those two times are indistinguishable."
 * Again, Robin is a connection between point A and point B in time, not point A in one universe and point B in another. When they return to 2017/2018, Robin is still flitting between the events of 2017/2018 and 2091. They are not distinct for her, they are mixed up, the timeline being mixed up in her head - the one timeline, not mixing up two universes in her head.
 * Daisy Johnson: "So, the lady who sees the future says that there isn't one. Super."
 * Robin sees the future, not another universe's future. So the dystopian 2091 she keeps seeing is the future.
 * Daisy Johnson: "The one who sees through time? Probably should've mentioned that."
 * Robin sees through time, not different universes. So the dystopian 2091 is just another point in time.
 * Just seeing the future, not another universe's future.
 * Robin Hinton: "Daisy! Daisy! He has a knife."
 * Robin's mind has gone to 2091, to the events happening in the same episode. Regardless of the interpretation, this scene is in the same universe as the events in 2091 of the same episode. However, this again demonstrates that Robin's powers connect across time and not across universes, which is relevant to other points where her powers are used - unless you are to assume that Robin is seeing the 2091 events of some further parallel universe that played out identically, but again, this is not the way the writers, or indeed the editing, present it.
 * Just seeing the future, not another universe's future.
 * Polly Hinton: "She can see the future, and I don't even have the power to know what she's feeling."
 * Robin sees the future. Everything she sees, including events from The Last Day in 2018-2022 and all the 2091 events, which she sees, are in the future of this timeline, not another one.
 * Just seeing the future, not another universe's future.
 * Melinda May: "And to do that, we have to find..."
 * Robin Hinton: "Phillip J. Coulson. He can put all the pieces together."
 * See April 13, 2018 The Honeymoon for discussion of this.
 * Dissected later.
 * Phil Coulson: "Yeah. And in that future, Earth is gone, and the last of humanity is enslaved by alien overlords. [...] There's a young Inhuman who's seen a better future. We're working toward that."
 * This is interesting, as it hasn't been previously mentioned that Robin can see a better future. She has only been said to be able to see the future. However, with the comment from The Last Day about Robin being right about changing time and in Inside Voices about Coulson putting the pieces together, it would seem that essentially, Robin can only experience (as her mind jumps around in time) the future of the timeline she's in, and can only clearly see the future, but can see glimpses of potential things to change the timeline, involving Coulson.
 * Just seeing the future, not another universe's future.

Result
No debate: '''Just seeing the future, not another universe's future. However, all the sources do come with the tiny chance that the characters are all mistaken.'''

How does the White Monolith operate?
Same universe and timeline.
 * No debate: It merely transports you across time, nothing else.
 * This would make it the same universe and timeline, they're simply going to the future.
 * Same universe and timeline.

How do Robin Hinton's powers work?
Same universe and timeline.
 * No debate: Just seeing the future, not another universe's future. However, all the sources do come with the tiny chance that the characters are all mistaken.
 * This would make it the same universe and timeline, with Robin seeing it in the future.
 * Same universe and timeline.

Marvel's Agents of S.H.I.E.L.D. (in-universe, the characters might be mistaken)
Same universe and timeline.
 * Jemma Simmons: "No reason to send a message back to Earth. We're already here."
 * Simmons realises they don't need to send a message back to where they have come from, since they're already here. This implies that it's the same place as where they left - they never left, just moved through time. It is not some alternate universe, it's their home, decades on. It is possible that Simmons is simply making an assumption that is incorrect, but this nonetheless appears to be the writers communicating this idea.
 * Same universe and timeline.
 * Melinda May: "This is Earth."
 * Phil Coulson: "We're in the future!"
 * Again, it's Earth (the Earth, not another), and they're in the future. And again, the agents could in-universe just be mistaken, but this nonetheless seems to be the writers communicating the idea.
 * Same universe and timeline.
 * Jemma Simmons: "It's all destroyed. Coulson, please, tell me it's impossible."
 * Phil Coulson: "I think we can all agree at this point that anything is possible. Glad you're alright. Your guy, Virgil. He didn't tell you anything else about his plan to bring us back from the past?"
 * They've been brought forward from the past, not another past. Same point about possible mistakes but the writers' intent.
 * Same universe and timeline.
 * Deke Shaw: "I'm just still trying to fit all these ideas inside my skull."
 * Phil Coulson: "And you haven't heard anything about a gateway? A rock that transports people?"
 * Deke Shaw: "If I had, do you think I'd still be here?"
 * Jemma Simmons: "There was no second monolith when I landed on Maveth."
 * Melinda May: "So, we'll have to find our own way back."
 * Jemma Simmons: "Well, I'm a biologist, but sure, I can invent time travel."
 * To get back, they have to travel through time, not back to their previous universe. Same point about possible mistakes but the writers' intent.
 * Same universe and timeline.
 * Deke Shaw: "Remember all that deranged garbage that Virgil was always spouting about people arriving from the past? I think you're looking at 'em."
 * The past again (if Deke is correct, but this nonetheless communicates the writers' intent).
 * Same universe and timeline.
 * Tess: "Stories from when we were kids. Some of the elders swore that a group called S.H.I.E.L.D. would come from the past to help us."
 * The past again (if Tess is correct, but this nonetheless communicates the writers' intent).
 * Same universe and timeline.
 * Daisy Johnson: "Does that line work in the future?"
 * The future again (if Daisy is correct, but this nonetheless communicates the writers' intent).
 * Same universe and timeline.
 * Deke Shaw: "I guess not."
 * Melinda May: "Fitz would be going out of his mind."
 * Jemma Simmons: "Time is strange. Somewhere out there, he's still fighting. But from our reference point, he's lived his life. Or not."
 * Fitz (not another Fitz, she's referring to "Fitz", her Fitz) would have lived his life from the point they are at, suggesting this is just the same timeline, decades later (if Simmons is correct, but this nonetheless communicates the writers' intent).
 * Same universe and timeline.
 * Natalie Abrams: "How far into the future are they?"
 * Jed Whedon: "We'll say definitively how far they're in the future in a few episodes, but the idea is 70 + years in the future."
 * Another comment about the future.
 * Jeff Bell: "We're X number of years in the future, and this is what this person knows."
 * Another comment about the future.
 * Same universe and timeline.
 * Daisy Johnson: "How could I split the world apart? My powers aren't that strong. I am not that strong."
 * Deke Shaw: "Maybe not yet, but you will be."
 * Daisy Johnson: "And how do you know that?"
 * Deke Shaw: "Because planet Earth went from smooth to chunky, and Quake is the one who did it."
 * Deke here implies that Daisy will go back in time and grow in power, then split the world apart, because that's the way it has always been, so that's what will happen, it just hasn't for her yet.
 * Daisy Johnson: "And you don't think I'd remember that?"
 * The simple response here, and what the conversation so far has suggested will be the response, is that she will go back and then it will happen.
 * Deke Shaw: "Well, actually, not according to the multiverse theory. You probably never heard of it, but in quantum physics, there's a theory that, for every universe, there are infinite parallel universes. So in my universe, you destroyed the planet. Maybe that just hasn't happened in -"
 * Deke switches gears into talking about the multiverse, which would essentially suggest he is wondering whether this is, in fact, not the Daisy who destroyed his world, but rather another universe's Daisy, which doesn't line up with the earlier part of the conversation. Unless he has essentially been saying, "Well, your power is still at a 7 but you're still only 28. I have evidence to suggest that you're going to grow in power over the coming months to a 10, because I know that Quake, by about age 29, is a power level 10, since the Quake in my universe is a power level 10 by about age 29, and you're at the very least very nearly the same person."
 * Still, this is a strange reply to her saying she doesn't remember. The reason is, "You haven't done it, at least yet," regardless of the multiverse - either she just hasn't done it yet from her perspective because she hasn't gone back to 2017 yet, or she just hasn't done it yet from her perspective because she was plucked from a universe at a time before she is set to do it. I guess the reason the conversation heads in this direction is that they can't know that Daisy will get back. So Daisy is essentially saying, "Well, I've just been taken from 2017 with no prospect of return, and I hadn't destroyed the world yet, so, unless you're saying I just happen to have destroyed the world before I left and I don't remember it...", to which Deke is then saying, "Well, sure, you've been plucked from 2017 with no prospect of return, but that doesn't change the fact that Quake destroyed my world, so, assuming you don't get back to 2017, how can Quake have destroyed the world? Well, maybe the answer is that you're a Quake from another universe, so it doesn't change the fact that in my universe's past, my universe's Quake destroyed the world." In which case, it's odd that he is in fact accusing specifically the Quake he's talking to of destroying the world - unless it's just because he's angry at Quake in general for destroying the world and angry at this one too because she's, for all intents and purposes, the same woman who would, in the same circumstances, end up doing the same thing - but also, it means his point is moot, as Daisy does end up going back in time. So we can likely just chalk this up to the characters not knowing they can get back yet, and the writers just finding a way to introduce the multiverse theory.
 * So, all else aside, it's still worth noting that the writers are introducing the multiverse theory here as a "Chekhov's Multiverse", clearly intentionally planted in the dialogue to in some way be part of the whole conundrum.
 * Daisy slaps Deke.
 * Daisy Johnson: "So what universe did that just happen in? Mine or yours?"
 * Deke seems to have essentially just said, "Technically, you might now have done it to my world," so it's a little odd that she slaps him - but it still makes sense, she's angry at him in general for the accusations levied against any version of her being capable of/culpable for the destruction of Earth.
 * The writers essentially confirm here what was already obvious, that if Deke had finished his sentence, he would have said "in your universe yet".
 * Leans toward separate universe, but maybe not.
 * Kasius: "Despite all I did for these humans, I found them clinging to their gods, their fairy tales, one of which was Quake. The Old Ones, rest their souls they used to tell the story of how S.H.I.E.L.D. would return one day from the past to save them. Now here you are."
 * Another comment about the past.
 * Same universe and timeline.
 * Kasius: "Sinara is concerned about the prophecy that others from the past might have come, as well."
 * Another comment about the past.
 * Same universe and timeline.
 * Leo Fitz: "Where are they?"
 * Enoch: "2-0-9-1. Earth Year 2-0-9-1."
 * Enoch is direct here. They're in the year 2091. Not another universe's 2091, just 2091. They have been shifted to another year, that's all.
 * Leo Fitz: "Why? Why did you send them through that thing?"
 * Enoch: "To fulfill a prophecy. This speaks of the future. They were needed there."
 * There has been a prophecy of the future in which the agents arrive from 2017, so the events of Episodes 1-4 should indeed be the future, not an alternate future, for them to be prophesied. A prophecy of the future would otherwise not see the agents come from 2017, since that would not be the future.
 * Same universe and timeline.
 * Leo Fitz: "You sent my friends into the future."
 * Another comment about the future.
 * Same universe and timeline.
 * Leo Fitz: "They're in trouble some 70 years in the future, and there's nothing I can do?"
 * Another comment about the future.
 * Lance Hunter: "They're stuck 70-odd years in the future, and our world's about to end."
 * Another comment about the future.
 * Polly Hinton: "How does this get Fitz to the future?"
 * Another comment about the future.
 * Same universe and timeline.
 * Leo Fitz: "You know, I spent 6 months locked up in an off-the-books military prison not to mention 80 years frozen in space all just hoping to find you and here you are."
 * This is again presented as the Fitz we've been following, not some sudden alternate universe Fitz. And again, yes, if it were a mostly identical parallel universe, he would say the same thing, but it's nonetheless presented by the writers as the Fitz and nothing else.
 * Leo Fitz: "You know, I realized something. The universe can't stop us. 'Cause we've crossed galaxies. We've travelled through time. We've survived the bottom of the Atlantic just so we could be together. Now, a love like that that's stronger than any curse. And you and I we are unstoppable together."
 * The whole sentiment of this quote is that no matter what the universe does to pull them apart, Fitz and Simmons will find their way back to each other. Not that Fitz has been through all of this to reunite with the next best thing, another universe (the main universe)'s Simmons. To propose to and marry what is accidentally another universe's Simmons and not his Simmons. They make their way back to each other no matter what, our Fitz and our Simmons. So, this is all the one universe, the one timeline.
 * Same universe and timeline.
 * Phil Coulson: "We came from the past to save the world."
 * Another comment about the past.
 * Same universe and timeline.
 * Alphonso Mackenzie: "Turbo! Man, it's good to see you! How the hell you get in the future?"
 * Another comment about the future.
 * Leo Fitz: "Uh, the long way."
 * Fitz came the long way to rejoin them. Not rejoin another universe (the main universe)'s version of his friends. They just had different means of travel to get from the same point A to the same point B, not ending up with different universes' versions of each other.
 * Same universe and timeline.
 * Leo Fitz: "Okay, if you guys really are gonna go fight a bunch of alien warriors, then you might be interested to know that, in the past, I hid a crate of S.H.I.E.L.D. tech in a wall on the base."
 * Again, this is very much presented as just the Fitz we've been following, who we've always followed, through Rewind, putting the tech in the wall, to now. And yes, again, if this were some identical parallel universe he would say the same thing, but there's no reason to assume that when the writers are simply presenting it as just... Fitz.
 * Alphonso Mackenzie: "Oh, that's what I'm talking about. Thanks, Turbo."
 * Elena Rodriguez: "Where?"
 * Leo Fitz: "Level 3."
 * Alphonso Mackenzie: "Oh..."
 * Elena Rodriguez: "Level..."
 * Alphonso Mackenzie: "... you gotta..."
 * Elena Rodriguez: "... 3?"
 * Alphonso Mackenzie: "... be kidding me."
 * Elena Rodriguez: "You mean the level infested with aliens that suck your blood?"
 * Leo Fitz: "Well, how was I supp- I feel like I'm not getting enough credit here. I have travelled through time and space to find you."
 * Again, Fitz has travelled through time and space to find "you", his friends, not a version of his friends from another universe (the main universe).
 * Same universe and timeline.
 * Melinda May: "I asked her why we were taken from the diner."
 * Phil Coulson: "And?"
 * Melinda May: "She said it was the last time we were all seen together."
 * This further affirms that the specifics of Deke's suggestion to Daisy were based incorrectly on assumptions about not returning to 2017 and just more about introducing the multiverse idea, since Jeff Bell said that what Deke means is perhaps they have been taken to the universe where they never left, but this shows that they were indeed taken from the diner (they're not seen together after since they're underground in the Lighthouse, in hiding).
 * As well as this, May is asking about her and her friends and Robin is recounting the history of this world to answer her question. In other words, these agents were last seen in 2017 of this world, not that another version of these agents were last seen in 2017 and/or that these agents were last seen in 2017 of another world.
 * Same universe and timeline.
 * Phil Coulson: "Last time I saw this it sent us to the future. How'd you get a piece of the monolith?"
 * Another comment about the future.
 * Same universe and timeline.
 * Leo Fitz: "Yeah, but the shard alone isn't enough, we need the whole monolith."
 * Phil Coulson: "It'd be great if Robin could help us fill in the blanks here. Daisy, you knew her first. Maybe you can get through to her."
 * Daisy Johnson: "I can try."
 * Melinda May: "If she helps us get home, maybe none of this ever happens."
 * May is hopeful that they can prevent this, though this works either way: changing time in some fashion, or making sure it doesn't happen in their universe, if it's a different universe.
 * Maybe same universe and timeline, maybe separate universes.
 * Leo Fitz: "Oh, not the girl's bloody time machine again. It's impossible. You cannot change time. It's fixed."
 * Fitz reaffirms his stance on time being fixed and unchangeable.
 * Melinda May: "What if it's not? She's been right about everything else, and for us to even have a chance, you and Simmons have to design the machine."
 * The agents are eventually successful, which makes this comment relevant. It is unlikely that the agents were successful but in a completely different way, with the agents being successful, the writers clearly intend for this to be relevant, that May was right: Robin has been right about everything else, with her help, they managed to "change time", finding that time is not "fixed". So their success is through some sort of method of changing time, not just their universe being separate and having a different future.
 * Same universe and timeline.
 * Leo Fitz: "Of course I do! Because we've tried! For all I know, we've tried a thousand times!"
 * This is a slightly odd phrasing, as Fitz is talking about how time cannot be changed and goes on to talk about a loop, implying he is talking about a time loop. Indeed, this chronologically is after his experiences in 2091 (or, if you believe this is an alternate universe, it is after identical events to Fitz's experiences in 2091), including the quotes from the next episode where Fitz comes to decide they are in a time loop, so that is his stance. Yet in a time loop, you technically cannot really count the number of times they have tried, as it's only one, just from a certain perspective it's coming back around an infinite number of times. This quote on its own would somewhat support the theory of a chain of parallel universes rather than a time loop, with him in fact referring to a chain of universes and how there could be a thousand where they've failed so far, who knows exactly? However, in context, it's likely he's simply just using a big number to express the infinite looping nature of a time loop and how from one way of looking at it, they could be on loop 1000, even though that doesn't quite make sense.
 * Leans toward different universe, but maybe not.
 * Leo Fitz: "Always ends the same! It's like a record that keeps on skipping, and we are repeating this loop again and again and again!"
 * Fitz refers to a loop here, which is why it seems like he didn't exactly mean one thousand. The frustration of a loop being that if you are to draw a line and enter into the loop section, you'll just go around and around without ever breaking out, and from that way of looking at it, you could in fact label the number of loops. However, really, they're all just the same one attempt that the line is drawing over again and again.
 * Melinda May: "Fitz, take a breath!"
 * Leo Fitz: "And every time, Jemma dies. They all die. Robin can't change it. Voss couldn't change it. Even Daisy couldn't change it. She saw the aftermath, and she still destroyed the world."
 * Fitz is referring to the 2091 events of the same episode. These 2018-2022 scenes are essentially presented, therefore, as flash-forwards from the agents' perspective (while flashbacks from the timeline's perspective). Fitz is written to be referring to the fact that Voss has shown Daisy what happens (in the 2091 events of this episode), yet she still then went back and, he believes, did it. The implication, it needn't really be said, is that when he's referring to the 2091 events of this episode, he's referring to the 2091 events of this episode, not identical events in another universe. And yes, again, he would say that same thing if it were in fact identical events in another universe, but that's not what the writers at all present.
 * Same universe and timeline.
 * Phil Coulson: "For Robin's sake, we need to make sure this world never comes to be."
 * Again, they are hopeful they can prevent this, but this could fit either way with changing time in some fashion or making sure their universe, if this is a different universe, does not end up the same way.
 * Same universe and timeline.
 * Samuel Voss: "Me and Owen were lockstep in almost everything. Always agreed to pull these people out of the past, but once they got here, we never saw eye-to-eye on that."
 * Another comment about the past.
 * Same universe and timeline.
 * Kasius: "You've never seen the Earth as it was. My father who had better vision than his race who shunned him, called it a hidden blue gem. He and his entire confederacy wanted it for their own. Gather my Inhumans, a fighting force to crush S.H.I.E.L.D.. With them out of the past, my father will then encounter no resistance. Earth waiting for his embrace."
 * Another comment about the past.
 * Kasius wants to prevent them from returning to 2017 so he can change time himself, in a different way to what the agents want. If they never get back, his father can win back in the 2010s, and time will be changed in whatever fashion. This does not work if the agents are simply returning to their parallel universe as he would have no way of knowing what his father in that universe is doing in 2017, or if he even exists. It only works through specifically wanting them to not return to the past he is familiar with, meaning they are returning to the past of this universe. And yes, again, Kasius could in-universe be mistaken, but this is what the writers are presenting.
 * Same universe and timeline.
 * 2017 Elena Rodriguez: "Hello? I'm here to help. What's your name?"
 * 2091 Elena Rodriguez: "Elena. It's good to see you."
 * 2017 Elena Rodriguez: "This is a trick."
 * 2091 Elena Rodriguez: "I thought the same thing when I was standing where you are."
 * 2091 Elena once stood where 2017 Elena is now, she had a conversation with her 2091 self when she was her 2017 self, suggesting a time loop again, that she literally was this 2017 self, though this does not go against the idea of an identical parallel universe she travelled to when she was younger, and there met that universe's 2091 Yo-Yo.
 * Same universe and timeline.
 * 2017 Elena Rodriguez: "How are you alive?"
 * 2091 Elena Rodriguez: "They killed me, brought me back to take my blood, my DNA, then again and again for years. They revive me when they want, kill me when they don't."
 * 2017 Elena Rodriguez: "What? H-How? How many times?"
 * 2091 Elena Rodriguez: "I held on to the thought of this moment."
 * 2017 Elena Rodriguez: "No. This is wrong."
 * 2091 Elena Rodriguez: "But this time, when they asked me how our team fought back, I tried to give them as little as I could. But I knew you were close. You and Mack. Mack! He's still alive. Hold him for as long as you can."
 * 2091 Elena knows that her 2017 self has limited time left with Mack, that he will die soon. This again should only work if they are in a time loop, as, if the 2017 Elena she's speaking to were to return to her own, distinct universe (the main universe), then there's no reason Mack has to necessarily go on and die. Again, one would have to assume that Yo-Yo is simply mistaken, thinking it's a time loop and also happening to act the exact same way and speak the exact same way to the point where nothing tells her otherwise. The writers are just presenting a time loop.
 * 2017 Elena Rodriguez: "What happens to Mack? What happens?"
 * Not "happened", "happens". 2017 Elena knows this to be in her future, since it happened in 2091 Elena's past, so it should be the same Elena, so all the same one universe and timeline. Yes, again, possible they're making a mistake, but the writers are presenting it as this.
 * 2091 Elena Rodriguez: "I practiced so many times what to say. I wanted to be better, save you from the pain. But seeing you - all the pain comes back."
 * 2017 Elena Rodriguez: "You've been here this whole time?"
 * 2091 Elena Rodriguez: "Stuck in the loop. Like you."
 * 2017 Elena Rodriguez: "The loop?"
 * 2091 Elena Rodriguez: "We make it back in time. But then we bring everything that's to come."
 * Again presented that they're in a time loop. They go back in time and then bring about this future. 2091 Elena says "we", she's referring to them as a collective because she is one of them, not a different universe's version, and "make it"/"then we bring everything" because she's recounting 2017 her's future as she recounts her past, telling 2017 Elena what will happen to her because it's what happened to her. It's a time loop.
 * 2017 Elena Rodriguez: "I, I don't believe that."
 * 2091 Elena Rodriguez: "I know. I don't think I did, either. Until I was on fire, reaching for Mack. And then there was nothing there."
 * 2017 Elena Rodriguez: "Well, you can tell me how to stop it, right? How do we change it?"
 * 2091 Elena Rodriguez: "I'm not sure you can."
 * A time loop that they're not sure it's possible to break out of, like Fitz believes.
 * Same universe and timeline.
 * 2017 Elena Rodriguez: "Whatever's coming, I'm not afraid to hear it. Tell me how to fight."
 * Again, it's coming for 2017 Elena because it's been for 2091 Elena, the future version of herself, not an older version of an alternate her.
 * Same universe and timeline.
 * 2017 Elena Rodriguez: "It's okay. Take it slow. Just tell me what you remember."
 * 2091 Elena Rodriguez: "I remember feeling helpless. Not being able to change people's choices. His choices."
 * 2017 Elena Rodriguez: "Mack?"
 * 2091 Elena Rodriguez: "No. Coulson."
 * We go on to then see the frustration Elena goes through as she is unable to change people's choices, like Coulson pushing Daisy to the forefront and trusting her too much. The implication is then that that leads to this Elena, they are the same Elena. Again, yes, possible they're just mistaken, but the writers are presenting it as such.
 * Daisy Johnson: "If I go through that portal, you know it's the beginning of the end."
 * Phil Coulson: "I don't."
 * Change of scene.
 * 2091 Elena Rodriguez: "We made it back home, and we fought to save the world from a future we knew was coming."
 * 2017 Elena Rodriguez: "We have to fight."
 * 2091 Elena Rodriguez: "Of course. But the more we fought, the closer it came."
 * Again, presented as a time loop. No matter what they did, the future was inescapable because it's predestined to be the way they've seen it to be.
 * Leaning toward same universe and timeline.
 * Daisy Johnson: "But we know this solution works. We can stop this today."
 * Phil Coulson: "No, it's not about today. It's about tomorrow. Even if we solve this problem, the world is never safe. The job goes on. We go on."
 * Change of scene.
 * 2091 Elena Rodriguez: "The team makes one choice, and it ruins everything."
 * 2017 Elena Rodriguez: "A choice to do what?"
 * 2091 Elena Rodriguez: "To save him."
 * We see this happen in the final episodes of the season, again implying the time loop is playing out exactly as it was for 2091 Elena, because it's the same events. This specific quote, though, isn't incompatible with the idea of just identical events going on to happen in another universe.
 * 2017 Elena Rodriguez: "What do you mean?"
 * Change of scene.
 * Phil Coulson: "Please."
 * Daisy Johnson: "Maybe I don't go with you. You know it's the right move. Coulson, as an agent of S.H.I.E.L.D., you trained me to fight. Now I'm making my stand, here."
 * Phil Coulson: "May trained you to fight... I need you to lead."
 * 2091 Elena Rodriguez: "Phil Coulson is dying. And you have to let him."
 * 2017 Elena Rodriguez: "Coulson... How? How does he die?"
 * 2091 Elena Rodriguez: "It's already begun. He's sick, and he knows it."
 * 2091 Elena should only be able to know Coulson is already sick and dying if it's a time loop. If this were simply a Coulson from a different universe to hers, then things could very well be different. She knows these things because she's been through them herself when she was the person standing in front of her. Now, yes, it's possible that she is just mistaken into thinking it's a time loop and nothing has indicated otherwise, and it's an identical universe with identical events, so Coulson does indeed happen to be sick. But that's not what the writers are presenting, and as mentioned, it would be highly unlikely that 2091 Elena would not get an indicator that it's not a time loop.
 * 2091 Elena Rodriguez: "We tried to stop it. Loyalty, it cost us the world."
 * Again, we see this event playing out in later episodes, presented as 2091 Elena knowing what will happen because it's happened to her, because it's all the same Elena. Same things about how it's possible for identical events and a mistake, but it's highly unlikely and not how it's presented.
 * 2017 Elena Rodriguez: "You heard all this, and still you couldn't change anything?"
 * 2091 Elena heard what 2091 Elena says when she was 2017 Elena, which is that way because it's a time loop. 2091 Elena didn't just hear another version of Elena in 2091, she "heard all this", as in she heard this conversation. Yes, you can fudge it that she just heard "all of this sort of thing in a very similar way", but the writers are presenting it as being literally the same conversation.
 * 2091 Elena Rodriguez: "I know. Stuck in the loop."
 * Again, in a time loop, not a chain of universes (if Elena is correct, but this nonetheless communicates the writers' intent).
 * Leans toward same universe and timeline.
 * Leo Fitz: "I've been here before, with Enoch. We made it."
 * Fitz has been here before. Not an alternate universe's identical version of here, just "here" (if Fitz is correct, but this nonetheless communicates the writers' intent).
 * Leo Fitz: "Hunter and I left the Zephyr cloaked just outside of town. I'll show you where it is."
 * Fitz knows Zephyr One is parked nearby, because he and Hunter parked it. Not that, back in his universe, he and Hunter left the Zephyr cloaked nearby, and luckily this universe's Hunter and Fitz (shown in Rewind) also did the exact same thing. "Hunter and I left the Zephyr." The Zephyr, the Zephyr of this universe, was left by "I", this Fitz (with Hunter). Yes, it's possible Fitz is just mistaken and, luckily, this universe was the same, but that is not what the dialogue has been written to say.
 * Deke Shaw: "I'm from the future."
 * Another comment about the future.
 * Alphonso Mackenzie: "We're gonna change the future anyway."
 * Mack is hopeful that they can change things, but they key word is "change". They are not fighting to prevent the future they saw from playing out in their universe, they are fighting because it is currently going to happen in their universe and they have to change it in some fashion. Yes, Mack may just be mistaken, but the agents, outside of those who do and don't necessarily agree with Fitz that time is fixed, are still nonetheless taking the fact that it is the future and just needs changing as a given. That that is the baseline fact they can at least all agree on.
 * Same universe and timeline.
 * Piper: "So, where on Earth were you hiding?"
 * Alphonso Mackenzie: "Well, technically, it was Earth."
 * It was Earth. The point of the comment is that it wasn't the location that was the problem, it was the time. The location is the same (broadly speaking), it was the same planet, just in the future. Not an a different location as well as a different time, just a different time, so not an alternate universe's Earth in 2091, just Earth in 2091.
 * Same universe and timeline.
 * Elena is carried, her arms just sliced off, like 2091 Elena's had been.
 * Elena Rodriguez: "It's all coming true."
 * Elena is scared about the fact that, already, events are happening to lead to the future they've just been to. Her arms have been sliced off, just as they were for the older version of herself. The worry is the fact that this serves as more proof that time cannot be changed, in a fixed loop.
 * Leans toward same universe and timeline.
 * Elena Rodriguez: "We have to stay and fight. The things I heard in the future they're all coming true. Faster than imagined."
 * Another comment about the future.
 * Again, things are playing out exactly the way they were always set to play out.
 * Same universe and timeline.
 * Alphonso Mackenzie: "So, we need more gravitonium to seal the rift for good, right?"
 * Leo Fitz: "Yeah, but that's something we haven't seen on this side of the future in a long time."
 * Another comment about the future.
 * Elena Rodriguez: "What I saw, what I heard... that's all happening. There's no future but the one I saw."
 * Everything is pointing, for Elena, to the fact that time cannot be changed, and that's the future. That's the only future.
 * Jemma Simmons: "No, that's not true. Hey! We can change it. We will change it."
 * Elena Rodriguez: "No. Nothing's gonna change it."
 * Again, the only optimistic stance for the agents is to "change" the future, not to prevent it from happening. It is a given, for all of them, that that is the future, just they're hoping to change it.
 * Elena Rodriguez: "I'm just trying to not lose faith. We're gonna change things."
 * Jemma Simmons: "That's the spirit."
 * Again, they're hoping to "change" things, the fact that it's due to happen as things stand is a given.
 * Same universe and timeline.
 * Elena Rodriguez: "Nothing's going to happen to me."
 * Alphonso Mackenzie: "You're damn right nothing's gonna happen to you. Not on my watch."
 * Elena Rodriguez: "No, Mack. Nothing can happen to me."
 * Alphonso Mackenzie: "What's that supposed to mean?"
 * Elena Rodriguez: "Well, think about it. You saw me in the Lighthouse. You know I make it to that point in the future. Nothing can happen to me until then."
 * This is another example of the time loop. Elena can't die until at least 2022 because they know she survived until at least 2022. She survived until at least 2022 because she doesn't die until at least 2022. She won't die until at least 2022 because she survived until at least 2022. She survived until at least 2022 because she doesn't die until at least 2022, etc.. This only works in a time loop, as otherwise there is nothing preventing her from dying (not that there's anything preventing her dying per se in a time loop, more just that it's knowledge that she simply won't). She could absolutely just die. It's possible she's merely mistaken, but it's not what the writers are presenting.
 * Same universe and timeline.
 * Alphonso Mackenzie: "We're actively working to make sure it doesn't come true, that means you could still die. I could still lose you. What then?"
 * Elena Rodriguez: "Well, then, we would have broken the loop."
 * The reason this is significant is because it would mean they are no longer bound by predestination if Elena dies sooner than she should. If this were simply a different universe to the 2091 they visited, then if Elena died now, then that would just be a tragedy that has happened in this version of events. However, in a time loop, if Elena dies, that means they're no longer bound by the loop and no longer have no scientific chance of being successful in saving the world. Elena's comment only has significance in a time loop.
 * Jemma Simmons: "It's such a confusing, grey area, but if we are going to change the timeline, we have to do things differently, make harder choices."
 * Again, the agents are taking it as given that the timeline is set this way, that the only hope of a good future is to "change the timeline". There is no question of "But what if we're in a different universe with a chance of making sure things play out differently in this one?"
 * Same universe and timeline.
 * Phil Coulson: "We traveled to the future. We saw the aftermath of that program."
 * Another comment about the future.
 * They saw the aftermath of the Destroyer of Worlds program, of what's happening currently. Again, the writers are presenting the 2091 events as the future, not a parallel universe's.
 * Hale: "You traveled to the future?"
 * Phil Coulson: "And back."
 * Another comment about the future.
 * Ruby Hale: "Did you actually travel to the future? 'Cause my mom doesn't believe that."
 * Phil Coulson: "Well aware how crazy it sounds."
 * Another comment about the future.
 * Ruby Hale: "So, if you really did see the future, then... tell me how I fail."
 * Phil Coulson: "What do you mean?"
 * Ruby Hale: "You told my mom that the Destroyer of Worlds cracks the planet apart, so what did I do wrong?"
 * Phil Coulson: "I hate to burst your apocalyptic bubble, but it wasn't you."
 * The significance of this conversation is that the reason it wasn't Ruby was because it was Daisy. If it had been Ruby, then it would have been "you". This again suggests a singular universe and timeline, because if it were another universe, it wouldn't have been "you", the Ruby he's speaking to, anyway (if Coulson is correct, but this nonetheless communicates the writers' intent).
 * Same universe and timeline.
 * Jemma Simmons: "So, if Yo-Yo subscribes to Fitz's theory that time can't be changed, then..."
 * They know "for a fact" that they were in the future, and the only way that that would end up not true, that Elena would be vulnerable, would be if they "changed" "time" in some fashion.
 * Alphonso Mackenzie: "She thinks she can't be killed."
 * Jemma Simmons: "Interesting."
 * Simmons is intrigued by this, realising, we later find out, that the science is sound and indeed, she shouldn't be able to die.
 * Same universe and timeline.
 * Deke Shaw: "And this place, 80 years from now, I'd survived on moves like that."
 * Deke was surviving in "this place", 73 years from now (he's rounding since it's 8 decades, 2010s to 2090s). So this place, plus 73 years, is the dystopian 2091 where Deke was living, making this the same universe and timeline. If not, then "this place, [73] years from now" would not at all be where Deke was living, a completely different future already, because the future would already be set to be positive. You can't rewrite a timeline as you go, the future is always going to be the way it is, the only hope for "change" is to branch a timeline. So the future, where they stand, is the dystopian 2091 they visited.
 * Jemma Simmons: "Can I pick your brain for a minute?"
 * Deke Shaw: "That's a weird saying."
 * Jemma Simmons: "I was hoping you could tell me more about our future."
 * "Our" future. Not the future of her and Fitz's alternate selves, but just simply her and Fitz's future, which Deke knows about, being from their future.
 * Deke Shaw: "I mean, you saw it. It sucked."
 * What they saw was "our" future, not another future.
 * Jemma Simmons: "No, I mean Fitz and me. Do you recall any evidence of major injury, any noticeable scarring, perhaps?"
 * Deke Shaw: "I don't remember you guys at all. I didn't even know your real names. Everyone in S.H.I.E.L.D. changed them when they were getting hunted down. I just knew you as Nana and Bobo. But you guys made it to the Lighthouse."
 * Jemma Simmons: "Good to hear."
 * Deke Shaw: "Mom talked about you a lot, but she never mentioned any health stuff. Pretty sure you were tip-top. You remind me of her. If you want, I could tell you stories about what you're a-"
 * Jemma Simmons: "I think it's best not to know too much. It's enough to know Fitz and I live long enough to create her."
 * Simmons now knows that they live long enough to have a daughter, because Deke knows they lived long enough to have a daughter, which only works if it's a time loop.
 * Jemma Simmons: "Mack said you believe you can't die."
 * Elena Rodriguez: "I know it sounds crazy, Jemma, bu-"
 * Jemma Simmons: "I don't think it's crazy. I believe it's true."
 * As Simmons was discussing with Mack, when subscribing to the idea that time can't be changed, then Elena cannot die in 2018, because they have knowledge that she survives 2018 in the timeline - only working if that were the same timeline.
 * Elena Rodriguez: "I'm glad someone understands."
 * Jemma Simmons: "I don't just mean you."
 * Elena looks at Fitz, and he gives a wry smile, as Jemma is referring to him and herself.
 * Elena Rodriguez: "You guys didn't see yourselves in the future."
 * Another comment about the future, and how that is what's significant for this idea of not being able to die - that they have to know from the future.
 * Jemma Simmons: "No. Deke is our proof. His mother... was our daughter."
 * Deke's mother is their daughter. Not another Fitz and Simmons', theirs, so he's from the future of this universe and timeline.
 * Elena Rodriguez: "Deke..."
 * Jemma Simmons: "Is our grandson."
 * He's their grandson, not another Fitz and Simmons', theirs, so he's from the future of this universe and timeline.
 * Elena Rodriguez: "Wow. I'm sorry."
 * Leo Fitz: "Thank you."
 * Jemma Simmons: "No, no, he's really quite sweet."
 * Elena Rodriguez: "Well, it makes as much sense as anything else. So we're the invincible three, huh? Now what?"
 * They know themselves to be, in a sense, invincible. Not in the sense that they're physically unable to be killed, but the fact that they simply have the knowledge that they don't die for years to come, meaning they won't die for years to come, so whatever they do, despite the odds, they just must survive. Only works under a time loop.
 * Elena Rodriguez: "I saw myself alive in the future. I want to use that to help..."
 * Another comment about the future.
 * Alphonso Mackenzie: "Damn it, Elena! That doesn't make you bulletproof. I thought you let go of that."
 * As discussed above, Elena knows she won't die, but isn't physically bulletproof. Mack, worried for her, looks at it the latter way.
 * Elena Rodriguez: "There are things I can't let go of. Things I learned in the future about this team, about Coulson, about you."
 * Another comment about the future.
 * Alphonso Mackenzie: "I don't want to hear about the future! Look, all I know is, right here, right now, you're in front of me. Safe."
 * Elena Rodriguez: "You can't protect me forever, Mack."
 * Alphonso Mackenzie: "Did you ever stop to think maybe you're alive in the future because I did? No, Fitz stays where he is. And so do you."
 * Mack's comment about her possibly only surviving because he advised caution is another example of a casual loop paradox, only working under a causal loop. He is positing, if she had listened to him: In 2018, Elena wants to be reckless, which likely would have got her killed. However, Mack cautioned her, which led to her surviving for years. Because she survived for years, she later found out she survived for years. Because she found out she survived for years, in 2018, Elena wants to be reckless, which likely would have got her killed. However, Mack cautioned her, which led to her surviving for years, etc.. He is specifically referring to her being alive in the future, not just that the version of her that they saw perhaps only survived in that universe because of the parallel version of him cautioning her.
 * Same universe and timeline.
 * Alphonso Mackenzie: "What the hell is this?"
 * Jemma Simmons: "An experiment. The test of a hypothesis. If that hypothesis is true, you'll see that you should let Fitz out."
 * Alphonso Mackenzie: "I already gave you my answer on that."
 * Jemma Simmons: "Yeah, but we want you to reconsider with all the facts, so, I'm going to prove that I can't be killed."
 * Alphonso Mackenzie: "What, you, too, Simmons? Do you know how all this sounds?"
 * Jemma Simmons: "Like science."
 * Again, for the same reasons, the science means that they cannot die in 2018. This means it's a time loop. If it were another universe, then knowing they survive through 2018 in that universe wouldn't cause any science to support the idea that they can't die now (if Simmons is correct, but this nonetheless communicates the writers' intent).
 * Alphonso Mackenzie: "No. Sounds like you're detached from reality."
 * Leo Fitz: "Don't look at me. I don't know what she's doing."
 * Jemma Simmons: "Well, what's an experiment without a little scepticism? So, each of these beakers contain a liquid. Three of them contain water, the fourth holds a phosphoric acid compound used in the hydraulics of Yo-Yo's arms. Highly toxic. One sip will make you sick, I mean, this much will surely kill you."
 * Leo Fitz: "What the hell? Jemma... No."
 * Jemma Simmons: "Yes, Fitz. I wouldn't be doing this if the science wasn't sound."
 * Simmons is confident in the science, that it's a time loop.
 * Jemma Simmons: "So, without knowing which is which, I will drink three of them, and since I can't be killed, I will happen to consume the three that just hold water."
 * Jemma only has a (0.25 × 0.33333 × 0.5 + 0.25 × 0.33333 × 0.5 + 0.25 × 0.33333 × 0.5 + 0.25 × 0.33333 × 0.5 + 0.25 × 0.33333 × 0.5 + 0.25 × 0.33333 × 0.5) 25% chance of survival, speaking simply about unfolding events, in picking three of the four beakers, and them all being safe. Except from her perspective, she has a 100% chance of getting that 25% chance outcome because she knows she gets it. It's like getting a glimpse into the future of next week's lottery numbers, a 1 in a million chance simply speaking, but from your perspective, you have a 100% chance of getting that 1 in a million chance. If this were a different universe, then she's just lucky, getting the 25% odds of success. In a time loop, there is more to it, as it's luck from one perspective but certainty from another, and the time loop establishes a paradox wherein she can't die, and it can be looked at the other way around: while yes, she makes it past 2018 in part because she survives here, she also survives here because she has to make it past 2018. It's a "chicken and the egg" situation, does she succeed at her 25% chance which gives her a 100% chance, or does she have a 100% chance meaning she succeeds at her 25% chance? She simultaneously has a 25% chance and 100% chance, rather than just a normal 25% chance.
 * Same universe and timeline.
 * Alphonso Mackenzie: "This is insane."
 * Elena shuffles the beakers.
 * Elena Rodriguez: "No looking."
 * Jemma Simmons: "I'm not looking."
 * Alphonso Mackenzie: "Are you kidd- Simmons! Are you serious?"
 * Elena Rodriguez: "Ready."
 * Alphonso Mackenzie: "Don't do it."
 * Leo Fitz: "He's right. Jemma, J-"
 * Simmons starts drinking from the first beaker.
 * Alphonso Mackenzie: "Don't. Don't. Simm- d-!"
 * Simmons finishes drinking from the first beaker.
 * Alphonso Mackenzie: "Simmons - Simmons, I need you to stop right now!"
 * Simmons starts drinking from the second beaker.
 * Leo Fitz: "N-! Oh, geez."
 * Simmons finishes drinking from the second beaker.
 * Jemma Simmons: "I will now drink the last one. And it will be water."
 * Leo Fitz: "No."
 * Alphonso Mackenzie: "No."
 * Jemma Simmons: "You would shoot me just to keep me from dying?"
 * Alphonso Mackenzie: "No, I - I'll wound you to stop this madness."
 * Jemma Simmons: "No. I don't think you will."
 * Alphonso Mackenzie: "Simmons, please. Please, Simmons, please don't."
 * Leo Fitz: "Jemma!"
 * Simmons starts drinking from the third beaker.
 * Alphonso Mackenzie: "Stop!"
 * Simmons finishes drinking from the third beaker. She gasps, seemingly feeling its effects.
 * Jemma Simmons: "Fitz..."
 * Simmons starts coughing.
 * Leo Fitz: "Jemma?"
 * Simmons falls and starts writhing.
 * Leo Fitz: "Jemma?! Jemma!"
 * Simmons is seemingly dying.
 * Alphonso Mackenzie: "Simmons! Fitz! Fitz, what do I do?!"
 * Leo Fitz: "She needs some alkaloid phosphate to counteract the toxicity!"
 * Alphonso Mackenzie: Okay, well where do I find it?!"
 * Leo Fitz: "I know where it is! Let me out!"
 * Elena Rodriguez: "Let him out! Please, let him out!"
 * Mack lets him out.
 * Leo Fitz: "Hang on, Jemma!"
 * Alphonso Mackenzie: "Hurry up!"
 * Elena speeds Mack into the cell and shuts the door.
 * Alphonso Mackenzie: "Elena, open the door! Now! Open the door! Open the door now! Ele-"
 * Simmons gets up. Mack and Fitz realise she was faking to trick Mack.
 * Leo Fitz: "A heads-up would've been nice. You sca-... Here."
 * Fitz pulls Simmons into a hug.
 * Leo Fitz: "Compliments on the performance, Dame Judi Dench. That's the longest you ever kept a lie going."
 * Jemma Simmons: "It wasn't all a lie, Fitz."
 * Simmons pours out the fourth beaker, and it fizzes on the tray, being the phosphoric acid compound.
 * Jemma Simmons: "I might've chosen that one. I didn't. Because we are invincible."
 * Despite the ruse, the experiment was still happening as intended, and despite the odds, Simmons survived. It's possible that she just survived due to luck (and, as explained above, there's an argument to be made that even in a time loop, she's still technically just surviving due to luck), but it's presented that she survived because that's the science, as she says. She cannot die, due to the time loop.
 * Leo Fitz: "And crazy, apparently."
 * Alphonso Mackenzie: "Let me out of here."
 * Elena Rodriguez: "I'm sorry, Mack. I know you don't understand. But I'm doing this to keep you safe."
 * Alphonso Mackenzie: "You're right. I don't understand."
 * Elena Rodriguez: "If, for some reason, I don't come back, it means..."
 * Jemma Simmons: "We've broken the time loop."
 * Again, there's a significance to one of them dying - a positive, despite the obvious negative - because it is evidence that they actually have a chance to change things. If they were in a different universe, it's just an unfortunate casualty. Sure, if they are in a different universe then clearly they still think they are in a time loop, and therefore would also mistakenly see the same significance, but again this involves assuming mistakes from the characters as well as going against what the writers are presenting.
 * Leo Fitz: "You know my feelings on that. It can't be broken."
 * Fitz reaffirms his stance again, this time instead of saying that time can't be changed, phrasing it that it would mean the time loop cannot be broken. The agents are again taking it as a given that they are in a time loop, the only question being whether they can break it or not.
 * Jemma Simmons: "Oh, is that what you'd tell our daughter, that her world can't be changed?"
 * Leo Fitz: "Maybe. Don't know. Haven't met her yet."
 * Jemma Simmons: "Oh, for goodness' sake."
 * Leo Fitz: "So maybe when I..."
 * Elena Rodriguez: "Guys!"
 * Leo Fitz: "... clear it..."
 * Jemma Simmons: "Can you..."
 * Leo Fitz: "... up..."
 * Jemma Simmons: "... not..."
 * Leo Fitz: "... then..."
 * Elena Rodriguez: Guys! You'll argue on the way. But if you really believe that, Fitz, then it means we're in no dang-"
 * Elena accidentally shoots the gun in her hand in their direction, but it miraculously misses both of them.
 * Again, the group survive despite the even lower odds. Assuming an approximate 5% chance of survival, then to survive this and Simmons' experiment becomes very unlikely without a cosmic factor. Again, with the cosmic factor of the time loop, you end up with a situation of simultaneous 100% chance of survival: do they survives in a scenario with a 5% chance of survival, which gives her a 100% chance, or do they have a 100% chance, meaning they survive in the scenario with a 5% chance?
 * Elena Rodriguez: "That was close."
 * Simmons is emboldened by another survival against the odds.
 * Jemma Simmons: "Let's go."
 * Again, Simmons feels further emboldened and sure that clearly the science is correct: they are in a time loop, unable to die because of it.
 * May walks to Robin with her sad drawing.
 * Melinda May: "Robin, is this why you had stopped drawing before? Because of what it shows?"
 * Again, Robin, who sees the future, has been seeing things such as her death and other events in the dystopian future. The dystopian future is the future, of this universe.
 * Same universe and timeline.
 * Deke Shaw: "Well, once again, my life depends on a crayon drawing of a crazy person, which is... great for me. Is May still with her?"
 * Daisy Johnson: "Yeah. I just cannot imagine bouncing back and forth between the past and the future like that. It sounds terrible."
 * Again, Robin goes back and forth between the past and the future, meaning the dystopian 2091 is in the future, not a different universe's future, with this universe's future being positive.
 * Same universe and timeline.
 * Glenn Talbot: "Where were you?"
 * Phil Coulson: "We were in the future."
 * Another comment about the future.
 * Deke Shaw: "Well, I thought that I left all this prophecy crap back in the future."
 * Another comment about the future.
 * Glenn Talbot: "So, this kid's from the future?"
 * Another comment about the future.
 * Same universe and timeline.
 * Jemma Simmons: "But there's always a chance that we've tried this before."
 * Leo Fitz: "More than a chance."
 * This would again suggest a time loop, specifically they ("we've") have tried this before, from a certain perspective.
 * Leo Fitz: "Previous selves probably came here, made all the same decisions still failed to change the timeline."
 * Referring to previous selves, however, does lean more in the direction of a chain of universes. However, the fact that Fitz is still talking about wanting to "change the timeline" would suggest just talking about changing events for one universe, one timeline. It's possible that Fitz is just, again, using a figure of speech for the perspective of a time loop repeating itself in iterations.
 * Leans toward separate universe, but maybe not.
 * Jemma Simmons: "You spoke to your older self in the future.
 * Her older self, not another version of her.
 * Same universe and timeline.
 * Jemma Simmons: "Did she give you any clues, any specific ways to stop this all from happening again?"
 * Elena Rodriguez: "We didn't have much time. I haven't told anyone this, not even Mack. I didn't want to put this on the team."
 * Leo Fitz: "What?"
 * Elena Rodriguez: "We have to let Coulson die."
 * Jemma Simmons: "What? That - That doesn't make sense."
 * Elena Rodriguez: "The other me, she said, trying to save him is what led to the end."
 * Elena calls 2091 Elena "the other me", suggesting more of a separate person than just her in the future. However, it's very possible she is just speaking loosely, the other Elena who was present in that room.
 * Leans toward separate universe, but maybe not.
 * Jemma Simmons: "Please tell me you still believe time can't be changed."
 * Jemma wants a reminder that time can't be changed, because they're in danger, and this would mean again that they cannot die.
 * Leo Fitz: "You want to debate that now? Isn't - Isn't that why we're here?"
 * Again, they are here with the hope that time can "be changed", that they can change it, not just prevent things from playing out similarly in this universe.
 * Same universe and timeline.
 * Jemma Simmons: "Still can't believe we survived."
 * Leo Fitz: "Me neither."
 * Jemma Simmons: "But you were so certain we'd be fine, "time is fixed" and all that."
 * Again, they survive despite the odds, caught in a firefight that would almost certainly get at least one of them at least badly injured. But they're fine, the explanation being that, most likely, this is just because they were always going to be fine, because they have to turn out fine. Yes, it's possible that they're mistaken and just happen to survive all of these things, but that's not the way the writers present it, nor is it likely - with Simmons unscathed from consecutive events with a 25% chance of survival, a roughly 22.4% individual chance of survival (if going by the idea of about 5% chance that both her and Fitz are unharmed, then there should be about a 22.4% individual chance each), and then a maybe 10% chance of being unharmed in this firefight, you're looking at a 0.6% chance of Simmons' survival in the last couple of days and she's not even harmed, unless in a time loop, where she has, in a sense, a 100% chance of being OK.
 * Leo Fitz: "I started having my doubts. Maybe your hopeful nature is rubbing off on me."
 * It is not that time is indeed fixed and they're just in a different universe, it's that time maybe is not exactly fixed, changeable in a certain fashion for their universe.
 * Same universe and timeline.
 * Ruby Hale: "Your little trip to the future? Coulson filled me in."
 * Another comment about the future.
 * Leo Fitz: "You realise that we have a choice to make?"
 * Jemma Simmons: "Yeah. Our hypothesis is being proven. We die, we break the loop. We don't fix this, we stop them."
 * Another comment about being in a loop and wanting to break it, and that if one of them died then it would be broken and they have a chance to save the world, but they don't feel able to allow that to happen.
 * Deke Shaw: "Well, I'm not even gonna be born for another 50 years, so maybe rethink "out there"."
 * Deke is due to be born in 50 years. If they were in a new universe, that would not be the case. Another Deke might be due to be born in 50 years (and in fact wouldn't be, since they change the timeline so that the humans aren't stuck together in the Lighthouse, so it's likely Deke's parents wouldn't meet, but at this point as far as they're aware the future would still be dystopian), but not him. They have to be in the same timeline he is from for Deke to be born in 50 years' time (if Deke is correct, but this nonetheless communicates the writers' intent). It's also clear that Deke, now they have returned to 2017 (now lived through into 2018), has ditched his initial comment about how it might've been another Daisy who destroyed the world since this Daisy had been plucked out of 2017. Since they've returned, there's no need for that, and he just agrees it's the same timeline.
 * Phil Coulson: "Well, let's hope it never happens, but if we can't change things then-"
 * Alphonso Mackenzie: ""Always be prepared," yeah, yeah."
 * Again, they're concerned about whether they can "change things", not make this universe have things play out differently (if Coulson is correct, but this nonetheless communicates the writers' intent)
 * Same universe and timeline.
 * Glenn Talbot: "Who is this? And when does this happen?"
 * Polly Hinton: "That's not really how it works."
 * Robin Hinton: "Soon."
 * Glenn Talbot: "Soon... And these? These all come true? We need to act on this."
 * Their universe is going to end up dystopian soon, again meaning there is no reason for the 2091 events to have been a different universe, since this universe's future is that dystopia anyway and the main motive for assuming the 2091 they visit is a different universe is to explain the change in events. But the change in events must be some sort of splitting off and not that this universe just turns out differently, as this universe's future is indeed dystopian, only then not being when they in some fashion change it.
 * Same universe and timeline.
 * Elena Rodriguez: "Well, we didn't pick you. Coulson made that decision and brought you back when he could have broken that loop right there!"
 * Another comment about the loop, and how they have had opportunities to definitely change things but failed, meaning they are still stuck in the loop.
 * Same universe and timeline.
 * Leo Fitz: "Hmm, I'm not sure you actually know what "multiverse" means."
 * Deke Shaw: "That every choice we make spins out a different timeline into the cosmos, and right now, there are infinite parallel universes."
 * This would align with the time loop, as at every decision point, another version of them might have spun out into a new, better, branch timeline, but the show is following the agents who make the same decisions every time heading toward that dystopian future, and then going around and around in that one through-line of a timeline. And then, when the show follows the agents into a branch not headed for the dystopian future, for those agents, the loop is broken.
 * Same universe and timeline.
 * Jemma Simmons: "But, if we succeed in ridding the planet of gravitonium, then we break that loop and prevent the Earth's destruction."
 * Again, hoping to break the loop. The loop is a given.
 * Same universe and timeline.
 * Elena Rodriguez: "You need to listen. You saw her, me in the future. I spoke to her. She warned me of all of this."
 * Another comment about the future.
 * Elena calls the woman she saw "me", so it's a future her, not another version of her (if Elena is correct, but this nonetheless communicates the writers' intent).
 * Alphonso Mackenzie: "I don't want to hear it, and I don't want to know."
 * Elena Rodriguez: "She was trying to help us, Mack, to prevent this. To keep me from losing you. She said things that -"
 * Alphonso Mackenzie: "Yeah, and it's making you crazy. This whole future thing has got you all acting crazy. I don't wanna know. I'm just trying to fix the problems right in front of me, not get my mind twisted trying to figure out what comes next."
 * Elena Rodriguez: "We already saw what comes next!"
 * They have already seen what's about to happen, so what they saw had happened is what is about happen, it's the future, not another future (if Elena is correct, but this nonetheless communicates the writers' intent).
 * Alphonso Mackenzie: "So you're willing to do anything, no matter who it hurts?! We've been through too much [...] In the future we swore. We swore we wouldn't lose ourselves."
 * Another comment about the future.
 * Melinda May: "She's following a lead."
 * Phil Coulson: "A lead on what?"
 * Melinda May: A way to keep you alive.
 * Elena Rodriguez: "What?"
 * Phil Coulson: "I don't want that. My orders are very clear about that."
 * Melinda May: "If there's a chance we can save you, don't you think I'd take it?"
 * Phil Coulson: "Right now, we all need saving from our new overlords out there, and our most powerful team member's gone."
 * Elena Rodriguez: "No, no, no, no, no. I killed Ruby for nothing. It didn't matter, it's all happening, right now. Everything she told me."
 * Phil Coulson: ""She" who?"
 * Elena Rodriguez: "This, right here? This is how we lose. I could've warned myself about a lot of things. Ruby, Hale, these aliens... but instead, she told me - Instead, she told me, "Coulson is dying, and we need to let him." I'm sorry, sir. I hated keeping this. I owe you so much. You're my family."
 * Again, events are playing out exactly how 2091 Elena told 2017 Elena they would despite everything they try, further implying the time loop.
 * Melinda May: "No, you're wrong. Robin said Coulson puts the pieces back together. And you're saying that we should've just left him to freeze to death in the middle of nowhere."
 * Elena Rodriguez: "I have to listen, May [...] She was me. She's lived through this, through the loop..."
 * It was an older her, who has lived through what she's currently living, because current Elena will be that woman. It's not another Elena.
 * Another comment about the loop.
 * Same universe and timeline.
 * Elena Rodriguez: "... who knows how many times?"
 * Another comment that suggests that a time loop is somehow quantifiable, which it isn't, but presumably just a manner of speaking - a perspective of entering and going around and around - rather than an indication of something else, considering Elena is saying that her older self has lived through the loop over and over, that the one Elena is stuck in the loop - not that it's a different Elena each time in a chain.
 * Leans toward separate universe.
 * Melinda May: "Exactly, you don't know. We haven't lost yet, and as far as we know, they can't get in here, - and until they do [...] you better believe we're gonna do everything possible to keep him alive."
 * The agents, as Elena is concerned about, are playing right into the exact future they are trying to avoid by trying to keep Coulson alive.
 * Alphonso Mackenzie: "Well, people in the future survive. There must be a way to stop them."
 * Another comment about the future.
 * Deke Shaw: "No, we didn't stop them."
 * "We", Deke is telling Mack about his experience in response to "the future", so he is from "the future" that Mack is referring to, the upcoming future, not some other future (if the characters are correct, but this nonetheless communicates the writers' intent).
 * Same universe and timeline.
 * Deke Shaw: "It's like the universe keeps reminding me that I should never have come back from the future."
 * Another comment about the future.
 * Same universe and timeline.
 * Phil Coulson: "I know it sounds crazy, but the alien running Earth in the future was a Kasius."
 * Another comment about the future.
 * Same universe and timeline.
 * Jemma Simmons: "Should work. It's just..."
 * Leo Fitz: "What Yo-Yo said... danger."
 * Jemma Simmons: "Yeah."
 * Leo Fitz: "Well, I've been thinking about that, and her warning was that trying to save Coulson ends the world, right? But what if, what if, what if we don't just try? What happens if we actually succeed? Jemma, what if there's another way to frame this?"
 * Jemma Simmons: "Coulson wasn't there in the future. You're saying we break the loop not by allowing someone to die, but by making sure they live?"
 * The agents are still trying to find a way to "break the loop", the loop being a given. This one is just a more positive loophole way of breaking the loop, rather than a tragic one.
 * Leo Fitz: "What if all we have to do is not fail?"
 * Jemma Simmons: "That's quite an audacious leap... especially from someone who once believed time cannot be changed."
 * Leo Fitz: "Maybe it's time to be audacious."
 * The hope is that time can be "changed" in some way, not that they're in a different timeline. Their only optimistic outlook is that it is not true that "time cannot be changed".
 * Phil Coulson: "That's the same writing that was in the Lighthouse in the future."
 * Another comment about the future.
 * Glenn Talbot: "You drew me. You see me in your head, don't you? You ever see me tearing the Earth apart, bringing something up from the ground?"
 * Robin nods.
 * Again, Robin has seen the future of the timeline, that this will happen in the timeline, not in another timeline.
 * Same universe and timeline.
 * Leo Fitz: "Where's Mack?"
 * Melinda May: "Uh, in the ship. He went to find Polly."
 * Leo Fitz: "May... neither of them make it... Oh, no..."
 * Neither of them "make it", not neither of them "made it". They are set to not make it, they are set to die, about to die, which they know because they learned from a point in the future that they previously died. Fitz doesn't know that the timeline is changed by this point (as Coulson has given Quake the serum), so from the perspective of assuming they are in the same position they were half an hour ago, then again, up to now, they have been in a time loop, what's about to happen is what happened when they were in the future (just it doesn't actually happen now, because the timeline is changed).
 * Same universe and timeline.
 * Jemma Simmons: "It's times like this I wish we didn't change the timeline."
 * The change in the timeline was what meant Fitz could end up in an accident, which is what Simmons is bemoaning. He was no longer bound by time to end up fine until 2091. He would never have been bound by time to end up fine until 2091 if they were always in a separate universe, it's specifically that they changed the timeline that meant anything could happen to him.
 * Same universe and timeline.
 * Enoch: "I presume Atarah wants to know how you were able to travel through time so that we may go back and save our world."
 * Jemma Simmons: "It's not that simple."
 * Atarah: "You deny that you meddled with the course of events?"
 * Daisy Johnson: "No, but we don't make a point of helping people play with time that have been trying to kill us."
 * Jemma Simmons: "It's complicated, we don't actually know how we did it."
 * They "meddled with the course of events", not just happening to travel to another universe and back and learning enough from their experience to prevent things from happening like they did in that universe. Making sure your universe would not end up like another one would not be meddling with the course of events, since it would just be participating in your universe's course of events being the way they are. You're not actually changing anything.
 * Same universe and timeline.
 * Deke Shaw: "And, and you sent a team out to find him, and you didn't tell me that, either?! That's not complicated, that just sucks!"
 * Alphonso Mackenzie: "It was the call made at the time."
 * Deke Shaw: "Well, maybe you shouldn't be making the calls because that was a bad one."
 * Alphonso Mackenzie: "No, it looked like you had other priorities besides being a part of this team."
 * Deke Shaw: "Oh, this team? You mean the team that I helped bring back from the dystopian future?"
 * Another comment about the future. No discussion ever of it being a different universe, in the future. It was the future, the dystopian one, that they have escaped and now they're on course for a non-dystopian future.
 * Same universe and timeline.

Jeff Bell, Jed Whedon, and Maurissa Tancharoen

 * Natalie Abrams: "How will Daisy handle knowing she supposedly caused the cataclysmic event that led to the end of the world?"
 * Jeff Bell: "I would say she's going to question everything about herself because she would say, "I didn't do it.""
 * Jed Whedon: ""I don't believe it because I didn't do it.""
 * Jeff Bell: ""I didn't do it, I would remember it if I had done it," but he'll say, "Yeah, but that's because you came to the future, what if you hadn't? The you that didn't, or whatever, could've done that.""
 * This gives some further context to the confusing conversation in the next episode. When Deke starts suggesting that they might be a different part of the multiverse, Bell's comment would suggest he specifically means that they've jumped out of the timeline but continued down the timeline where they're supposed to have stayed and then arrived in the future of a timeline where they never left. This is disproved by the rest of the season and the evidence that the agents always go to the future and then return, but still end up destroying the planet. I go into it more in that next episode's discussion.
 * Leans toward separate universe, but maybe not.
 * Mike Avila: "But you did seem to leave the door open for a possible Fitz return, judging by what Jemma was talking with Coulson about in the aftermath."
 * Jed Whedon: "Right. Everybody got zapped to the future, and zapped back, plus Fitz.
 * Another comment about the future.
 * Same universe and timeline.

Marvel's Agents of S.H.I.E.L.D. (factual)
Same universe and timeline.
 * Leo Fitz: "It's a cryo-freeze chamber."
 * Lance Hunter: "What?!"
 * Leo Fitz: "Yeah. I'm taking the long way there. Gonna sleep for 74 years."
 * Again, it's the future of this timeline. Fitz is about to sleep for 74 years so he can wake up in 2091, where he can join his friends, because they're in 2091. Not another 2091. While it's possible that Fitz is mistaken, because they're in an alternate 2091, it shouldn't be possible for Enoch to be wrong, given his knowledge via Robin.
 * On-screen: "74 years later".
 * This confirms it. Essentially, saying "74 years later" is like hitting super fast fast-forward. The show just fast-forwarded through 74 years of the timeline to get to 2091, where the agents are. He got there simply by living long enough (by being frozen). The agents are in 2091, it's that simple. This isn't "74 years later, in another universe", it isn't "now let's switch to focus on another universe's Fitz", it's just the continuation the episode's narrative, following Fitz through.
 * Same universe and timeline.
 * Leo Fitz: "Gravitonium would explain why it's held together."
 * Jemma Simmons: "And maybe why it was cracked apart."
 * Leo Fitz: "But it being here also means that... It's true. Robin, May it's all true. This is the same design from the Lighthouse, so unless someone else just... happened to come up with the exact same idea... we did this, in the past, after we've lived this moment."
 * Jemma Simmons: "Yeah, the causal loop paradox. We'd only know how to design it because we'd already seen it."
 * Fitz and Simmons have realised that they've just been given the idea and method of installing gravitonium into Zephyr One, which will then allow them to do it in the past, leading to it being here now to give them to idea, leading to allowing them to do it in the past, etc.. So, they are in a time loop. That's what Fitz is worried about, he's just seen proof they're stuck in a loop.
 * This further suggests a time loop over a chain of universes, not least because Simmons explicitly says "causal loop paradox". The chain of universes interpretation is that the Universe B agents travel from 2017B to Universe A's dystopian 2091, 2091A, before coming back to Universe B's 2017, 2017B, the Earth is destroyed in 2018B, then 2091B is dystopian in the exact same way. Universe C's agents travel from 2017C to 2091B, before coming back to 2017C, the Earth is destroyed in 2019C, then 2091C is dystopian in the exact same way. Universe D's agents travel from 2017D to 2091C, and so on. However, as Fitz is establishing, they get the idea and understanding over the gravitonium from seeing it in 2091, leading them to do it when they get back to 2018, leading to it being there in 2091. But the chain of universes interpretation would mean that the gravitonium has to be installed in the exact same way in Universe A for them to see it in 2091A and get the idea, to then be able to do it in 2018B. But Universe A's agents would never have travelled to another, dystopian universe's 2091, so would never have got the idea or method to install it in that timeline, so it can't be fitted in 2091A for them to learn for Universe B, etc.. This just doesn't fit with a chain, as it requires an initial different universe.
 * This touches on a wider point: The problem of an initial universe. This interpretation requires numerous identical universes, including Universe A, for the agents of Universe B to experience the same 2091 events when they visit 2091A. Except Universe A's agents would have never travelled to a dystopian 2091, so events are, by default, different, let alone the fact that so many events surrounding the destruction of Earth and dystopian future revolve around the fact that the agents got to see the dystopian future. Universe A would have no way of playing out the same way to kick off a chain.
 * Leo Fitz: "Well, we're done for. This is proof."
 * Jemma Simmons: "Uh, I don't know if that's true."
 * Leo Fitz: "Yes, it is. Think about it. There is nothing that we do that matters. This is a bloody time loop. We're doomed to fail."
 * Fitz discusses the time loop they're stuck in, and that due to that, they're bound by predestination.
 * Jemma Simmons: "If we did this, do you know what I see? Proof we make it back."
 * Simmons looks at it the more optimistic way, but it's the same concept. They have to now make it back because in 2017 in the timeline, they made it back. That's just the way it is.
 * Same universe and timeline.
 * 2017 Elena Rodriguez: "This isn't real."
 * 2091 Elena Rodriguez: "I wish it were true. An LMD or a Framework illusion - but it's me. I'm you."
 * 2017 Elena Rodriguez: "How? I-"
 * 2091 Elena Rodriguez: "I waited so long to see myself again, still with hope in my eyes."
 * She knew she was going to see her younger self, which again tells us the agents are in a time loop. If 2091 Elena has lived out her life in her own universe, the one they're in now, distinct from the main universe, then she would have no way of knowing that another universe's 2017 Yo-Yo would join her in the future, because she simply wouldn't know the exact way the future would play out. The only way that would work would be if they still thought it was a time loop and were just mistaken, but things still played out the same anyway. It is much more likely that this is simply a time loop, with Yo-Yo knowing she will see her younger self again.
 * Same universe and timeline.
 * 2091 Elena Rodriguez: "I want to. I want to help you fix the mistakes. I want to tell you something different than last time. But the more I talk, the more I hear my words echo all over again."
 * This is an indicator of the time loop. No matter what she says, whatever she tries, she finds herself saying the exact same thing she heard when she was her younger self, because it is the exact same thing. If this were a different universe to the one her younger self visited, then she would not be bound to say the same thing she heard, as she's not the same person. She would be able to change even one word, and that would be enough of an indicator that they're not stuck in a time loop. While identical versions of the same character in the same situations might say the same thing, Elena is trying with every word to say something different to what she heard, and wouldn't be unable to. While you might then think that, well, the previous version was also trying to say something different, so she's in the same situation so would try the same thing, this Elena would simply be trying to say something different to the last one, the only one she's aware of, just with the script in her head and all she has to do is say one word differently. She can't, no matter what she does, because it is the exact same conversation, in a time loop.
 * Same universe and timeline.
 * 2091 Elena Rodriguez: "But you can forge a different fu- Even as I say the words, I realize I've heard them before."
 * This frustration is a good example of the mechanics of a time loop. Every single word Elena speaks is the same thing she heard when she was younger, because it's the same conversation. She heard herself say "But you can forge a different fu-" and then realise, "Even as I say the words, I realize I've heard them before" and say that aloud, likely realising as she says that that she's heard it before, and so on. She can try every moment to say something different to what she heard but whatever she does, it is unavoidable, because what she saw was this conversation. If what she saw was in another universe, with a chain of universes, then she would be able to break away and say even one word differently, not bound by the fact that it is literally the same conversation.
 * 2017 Elena Rodriguez: "Are you telling me to go back and change the world, or are you warning me that I can't?"
 * This is the dilemma, in summary. Hoping that time can in some way be changed, but semi-resigning to the fact that it's probably not possible and there's no clear method to somehow change it, which would only be this way if it's the same universe and timeline.
 * Same universe and timeline.
 * Jemma Simmons: "Is something wrong?"
 * Alphonso Mackenzie: "Just that, lately, she's been acting like she's bulletproof, like nothing can stop her."
 * Jemma Simmons: "Well, that is not an uncommon attitude for our team."
 * Alphonso Mackenzie: "No, this is different. Yo-Yo saw herself in the Lighthouse, so now she knows for a fact that she lives far into the future."
 * Elena knows "for a fact" that she survives into the future, since she found out in the future that she survives that long. This implies that the agents know "for a fact" that that is the future, not another universe's future, further negating the point that the agents might simply be mistaken.
 * Same universe and timeline.
 * Robin wanders the plane.
 * Polly Hinton: "At least when she would draw, I'd have a window into her world."
 * Daisy Johnson: "Do you remember what her last drawing was?"
 * Polly Hinton: "I have it."
 * Polly hands Daisy the drawing.
 * Polly Hinton: "Do you know what it means?"
 * Daisy has a personal flashback to Robin's death.
 * Robin saw her 2091 death from The Last Day, meaning that's in the future of this timeline, not another one. One could argue that it's just her seeing this timeline's version of her death, identical to the one in The Last Day, but in that case it defeats the purpose of the alternate universe theory, specifically intended for the future of this universe to not be dystopian.
 * Daisy Johnson: "I'm not sure."
 * Robin gets to the cockpit, where May is.
 * Robin Hinton: "Mom? Mommy?"
 * She hugs May.
 * Robin is seeing the future, where May becomes her adoptive mother after Polly dies. This again means that the future of this universe is indeed dystopian, so there is then no reason for the dystopian future of the first half of the season to be anything other than this dystopian future, when that's how it's presented. Robin is specifically referring to the 2018-2022 scenes from The Last Day, in the future of this universe.
 * Robin Hinton: "I missed you. I told you Flint would get you back!"
 * Melinda May: "You did! You were right."
 * Robin is referring to when she, experiencing things as her elderly self, told May about Flint in 2091, in The Last Day. Therefore, that is the future of this universe. Again, if arguing that The Last Day was just an identical event in another universe, that would be pointless, since this still proves that the same event happens in this universe's future, therefore defeating the purpose of the argument in the first place, when, if this universe is set to have identical events, the events might as well be just the same ones, in this universe's future, as presented.
 * Same universe and timeline.
 * Malachi: "Leopold Fitz should not be here."
 * Jemma Simmons: "Agreed. He should be with us, back on Earth."
 * Malachi: "Earth is where he died. Over a year ago, if I'm not mistaken."
 * The Chronicoms are going after the agents because they want to learn how to change time, as is later revealed. They are pointing out that Fitz being both dead and on Kitson is evidence of time travel and changing the timeline (in whatever fashion), not cross-universe travel, which would be the case if the dead Fitz had come from another universe. They just travelled in time.
 * Same universe and timeline.

Result
Debatable: Same universe and timeline.

Is the Marvel's Agents of S.H.I.E.L.D. 2091 the future of the universe the agents were in when they left 2017, or were they taken to a separate universe's 2091?
Caused by something to do with the changes of the universe.
 * Debatable: Same universe and timeline.
 * So, the answer does not rely on three separate universes.
 * Caused by something to do with the changes of the universe.

Marvel's Agents of S.H.I.E.L.D. (in-universe, the characters might be mistaken)
One Fitz at two different ages simultaneously in 2018, timeline splits, you now have two untethered Fitzes of different ages.
 * Phil Coulson: "And now he's frozen, out in deep space somewhere, no idea he's already solved it."
 * There are two versions of Fitz around post-May 2018, one 104 years old (not biologically) who has just died, and one who is 30 years old, still out there, frozen. Fitz lived through to 2091, then doubled back on himself so there are simultaneous Fitzes from December 2017. When the timeline splits in May 2018, there are two Fitzes, now separate, unbound. The 104-year-old dies, the 30-year-old is still frozen out in space and can be retrieved.
 * Imagine a piece of string next to a ruler, starting at point "1987.632cm". It continues through to "2091.999cm", where a portal is positioned. The string continues on, through the portal and out the other side, which is next to the string back at "2017.925cm", and the string continues again, side-by-side with its earlier self. Then, at "2018.412cm", a guillotine slices across, as the timeline splits off. The one piece of string is now two, one snipped about 30.8cm into its length, one snipped about 104.9cm into its length. Originally two points on the same piece of string, but now two loose ends, with their own futures, unbound. The 104.9cm one dies almost immediately, but the 30.8cm one is still out there to be found, essentially an old save file of Fitz from 74 years back in his life (but 73.6 of those spent frozen).
 * Another way to look at it is to look at the fork of the timeline. Follow it from the perspective of Fitz's life. His life goes as normal up to his 6 months imprisoned at Blue Raven Ridge. Fitz is then frozen. 6 months later, we hit the fork in the timeline. Going down the bad branch, he continues to be frozen. Going down the good branch, he comes out of freeze, and we get the Season 6 Fitz, who we will continue to be following in the show. The bad timeline, the frozen Fitz is still frozen until 2091. He goes back in time to December 2017. Over 5 months later, we hit the fork in the timeline again. Going down the bad branch, he ends up in the Lighthouse in the 2018-2022 events of The Last Day. Going down the good branch, he dies in an accident as the rubble falls on him. From Fitz's perspective, it's a two-pronged split, and then a further two-pronged split on one of those prongs. From the timeline's perspective, those splits are actually the same one split, with the prongs bending back on themselves. In either timeline, post-May 2018, there are always two Fitzes. In the bad timeline, there's 30-year-old frozen Fitz and 104-year-old Lighthouse Fitz. In the good timeline, there's 30-year-old soon unfrozen Fitz and 104-year-old dead Fitz.
 * One Fitz at two different ages simultaneously in 2018, timeline splits, you now have two untethered Fitzes of different ages.

Jed Whedon
One Fitz at two different ages simultaneously in 2018, timeline splits, you now have two untethered Fitzes of different ages.
 * Jed Whedon: "But Fitz traveled to the future the long way. He basically slept in cryo-freeze for 80 years. So there are technically two Fitzes in this timeline, so we just killed one of them."
 * Describing how Fitz doubled back on himself, leaving two Fitzes around. The use of "this timeline" then seemingly is used to explain how they have two disconnected Fitzes around now they're in this timeline, rather than being the one Fitz at two different points in his life as before. Then the older one died.
 * One Fitz at two different ages simultaneously in 2018, timeline splits, you now have two untethered Fitzes of different ages.

Result
Debatable: '''Not three universes. One Fitz at two different ages simultaneously in 2018, timeline splits, you now have two untethered Fitzes of different ages.'''

Films (in-universe, the characters might be mistaken)
No.
 * Karl Mordo: "Unstable dimensional openings. Spacious paradoxes! Time loops!!! You want to get stuck reliving the same moment over, and over, forever, or never having existed at all?
 * The rest of the time-related things in Doctor Strange are done without complication. What he does with the Time Stone is merely turn the apple and book backwards and forwards in their personal existence, and then he does the same to the city in Hong Kong, just on a grander scale. There is no actual turning back of time. Then the time loop is fairly clear, Strange flies off then traps himself and Dormammu in a loop while no time is passing outside of their bubble, then once he's done he returns, immediately after he left. So, the time loop described here is not a problem with time travel and changing timelines and things. The meaning behind what Mordo says about "never having existed at all" is unclear, if this implies some rewriting of a timeline (said elsewhere to be impossible) or just that some other mistake he might make when meddling with something as powerful as an Infinity Stone that controls time could erase himself from existence in some manner.
 * Maybe yes, maybe no.
 * James Rhodes: "If we can do this - you know, go back in time - why don't we just find baby Thanos, you know, and...?"
 * Rhodes mimes choking baby Thanos.
 * Smart Hulk: "First of all, that's horrible..."
 * James Rhodes: "It's Thanos!"
 * Smart Hulk: "... And secondly, time doesn't work that way. Changing the past doesn't change the future."
 * You can't just rewrite time in the way many films do time travel.
 * Scott Lang: "We go back, we get the stones before Thanos gets them... Thanos doesn't have the stones! Problem solved!"
 * Clint Barton: "Bingo."
 * Smart Hulk: "That's not how it works."
 * Clint Barton: "Well that's what I heard."
 * Smart Hulk: "Wait, by who? Who told you that?"
 * James Rhodes: "Star Trek, Terminator, Time Cop, Time After Time..."
 * Scott Lang: "Quantum Leap!"
 * James Rhodes: "... A Wrinkle in Time, Somewhere in Time..."
 * Scott Lang: "Hot Tub Time Machine!"
 * James Rhodes: "Hot Tub Time Machine! Bill & Ted's Excellent Adventure, basically any movie that deals with time travel..."
 * Scott Lang: "Die Hard!... No, that's not one."
 * James Rhodes: "... This is known."
 * Smart Hulk: "I don't know why everyone believes that but that isn't true."
 * This is all them discussing again the idea that you can't just rewrite time in the way science fiction films often suggest.
 * Smart Hulk: "Think about it: if you travel to the past, that past becomes your future..."
 * When you travel to 2012, that chunk of the past you are now living in is now in your present and future.
 * Smart Hulk: "... and your former present becomes the past."
 * 2023 is now in your personal past.
 * Smart Hulk: "Which can't now be changed by your new future."
 * Just by being in 2012, nothing you do can change your personal past of your 2023.
 * Nebula: "Exactly."
 * Scott Lang: "... So Back to the Future ' s a bunch of bulls**t?"
 * Just another affirmation of the classic sci-fi rules of rewriting time being wrong.
 * No.

Marvel's Agents of S.H.I.E.L.D. (in-universe, the characters might be mistaken)
No.
 * Daisy Johnson: "I can change it."
 * Leo Fitz: "No."
 * Daisy Johnson: "We can reverse-engineer the visions, figure out where this went down, and get there ahead of it."
 * Jemma Simmons: "Save that poor man."
 * Leo Fitz: "You can't. I mean, fourth-dimensionally speaking, is all. If you saw the future, then... that's the future."
 * Fitz is explaining that time already all exists, fourth-dimensionally speaking. We just happen to be currently perceiving a certain point in the timeline.
 * Daisy Johnson: "I don't want to believe that. I can't explain how it felt, but it was awful. I felt so helpless. I was inches away from him. I have to save him."
 * Lincoln Campbell: "Edwin called in with your name for a reason. Maybe you're meant to change it."
 * Phil Coulson: "And we know what this homeless man, Charles, looks like."
 * Melinda May: "And we're running a search."
 * Phil Coulson: "If Daisy can remember details about the location and we get there in time, we -"
 * Leo Fitz: "Guys, there is no time. She glimpsed the fourth dimension. Time is an illusion. It's how we perceive the fourth dimension. Simmons..."
 * Jemma Simmons: "It's mathematics. He's talking about space-time."
 * Fitz is talking about space-time and how the fourth dimension just already is.
 * Leo Fitz: "How do you-? How can I explain this? Right..."
 * Fitz picks up a wad of paper.
 * Leo Fitz: "We're 3-D, yeah? Okay, but imagine, imagine we lived in a 2-dimensional existence. Flat, just like a piece of paper. We wouldn't be able to conceive of three dimensions, of, of, of a, a cube or... anything that's not 2-dimensional, okay?"
 * Phil Coulson: "Yeah."
 * Leo Fitz: "Right, so, we flat, paper people..."
 * Fitz draws a line along the side of the wad.
 * Leo Fitz: "... would perceive this 3-dimensional cube as many separate 2-dimensional moments. As..."
 * Fitz flicks through the paper wad like a flip book.
 * Leo Fitz: "... time passing, the point on the line traveling through space and time."
 * Jemma Simmons: "But, in fact, the cube, the line, is fixed."
 * This is a good explanation of the space-time continuum and how time is already fixed, with present just being our perception in a current 3-D moment and either side of our current moment being labelled past and future.
 * Leo Fitz: "Yeah, it's just sitting there. There's no future. There's no past. It just... it just is. And nothing you can do will change that."
 * Time already sits the way it was and always will be that way. If you glimpsed the future, then you have glimpsed the future. This turns out true, everything plays out as foreseen, both in this episode and then in the rest of the season leading up to Lincoln's death in Ascension.
 * No.
 * Leo Fitz: "Oh, not the girl's bloody time machine again. It's impossible. You cannot change time. It's fixed."
 * Fitz reaffirms his stance on time being fixed and unchangeable.
 * No.
 * Leo Fitz: "Nothing we do matters. Because we can't change time."
 * Fitz reaffirms his stance again.
 * No.
 * Jemma Simmons: "No, Fitz, just tell me it's against the law of physics, I need that right now."
 * Leo Fitz: "The perception of time is an illusion."
 * Jemma Simmons: "Last mag."
 * Leo Fitz: "According to Hermann Minkowski, space-time -"
 * Jemma Simmons: "Oh, you know what? I was wrong, it's not helping!"
 * Fitz again states that time is fixed, with Simmons specifically saying to rewrite time would be "against the law of physics".
 * No.
 * Deke Shaw: "I mean, besides, according to Fitz, if the world doesn't crack open and you break the time loop, I'll just blink out of existence anyway, so it's just one more vacancy, right?"
 * Fitz believes there is a singular timeline, so the only way they could break the time loop would be to rewrite time (which he doesn't think is possible, but if it is), thus causing Deke to blink out of existence. Fitz is later shown to be wrong - Deke stays around - but they did break out of the time loop, so this means they didn't rewrite time, Fitz was right about that not being possible, as also discussed in Avengers: Endgame.
 * No.

Novels (in-universe, the characters might be mistaken)
Yes with the Time Stone.
 * Jane Foster: "The green Time Stone allows its wielder to go backward or forward in time, changing whatever they see fit."
 * Maybe it is possible to rewrite the singular timeline, but only through the use of the Time Stone, since Infinity Stones essentially have control over the universe and the ability to break physics.
 * Yes with the Time Stone.

Anthony and Joe Russo
No.
 * Joe Russo: "... it's just like what Hulk said, what happened in the past has already happened. If you go back to past, you simply created a new reality."
 * Here, Joe Russo reiterates that you cannot rewrite time.
 * Joe Russo: "The characters in this movie created new timelines when they went back to the past, but it had no effect to the prime universe. What happened in the past 22 movies was still canon."
 * He reiterates the point about being unable to rewrite time and therefore change the main timeline.
 * No.
 * Joe Russo: "It's not butterfly effect."
 * The people involved with the film seem to define the butterfly effect as specifically rewriting the one only existing timeline. So, again, a comment about not rewriting the one only existing timeline.
 * No.
 * Sonaiya Kelley: "Okay, be honest: Do you guys understand everything about how time travel works as explained in the movie or are there still loopholes even for you?"
 * Anthony Russo: "In the movie, the Hulk is very explicit about what our rules are, which is you cannot change the present by altering the past."
 * Here, Anthony does get right what Hulk says (assuming the next part is no longer referring to what Hulk says) without adding any extra stuff like some others in some other quotes. Simply that you cannot change things even if you're changing the past.
 * No.
 * Anthony Russo: "Here's the most important thing about time travel: It doesn't exist."
 * Joe Russo: "According by the rules of the movie, as stated by the Hulk and by the Ancient One, we go to great pains to tell you that Back to the Future is bulls**t."
 * Just another reiteration of the idea of not rewriting one single timeline.
 * No.
 * Joe Russo: "The Hulk says if you're in the present and you go back to the past, you cannot affect the present because it has already occurred. That now becomes your past. Right? And if you're [currently] in the past, this is now your present."
 * That's all true, correct, and fine.
 * No.
 * Joe Russo: "If you're paying attention to what the characters are saying, they're each talking from their own perspective. Banner is a man of science and when he's explaining to everyone in that room why movies are wrong, he's talking about it from quantum physics standpoint. He says that if you leave the present to go to the past then that present has become your past. It has always happened. You can't change it by influencing the past."
 * Simply, you can't change time, you can't rewrite a timeline.
 * No.
 * Joe Russo: "So, you have to travel to the past, come back to that present and then fix it moving forward because you can't alter it from back there."
 * Again, you can't rewrite the timeline.
 * No.
 * Joe Russo: "We didn't want to play by the Back to the Future rules, we wanted to do something different."
 * Another standard "we're not following the Back to the Future rules of rewriting the one single timeline" comment.
 * Joe Russo: "The Hulk tells you in the film, he says you cannot affect the present by going to the past, because the present has always happened."
 * That's not what he says, he says you cannot affect the present by changing the past. However, he does essentially say you can't affect the present because it's always happened, and through that, he has indirectly said that you cannot affect the present by going to the past at all, as Joe says. That's all fine, it's the same as the talking about not using Back to the Future rules.
 * No.
 * Joe Russo: "So it's very different than, you know, Back to the Future which is linear, right?..."
 * Chris Hewitt: "Yes."
 * Joe Russo: "... Is that you can affect your present by going back to the past. That is not the case in, sort of, you know, any sort of quantum physics approach to time travel."
 * Chris Hewitt: "Yeah, it allows you to do things like have Nebula - our Nebula, so to speak - essentially kill her..."
 * Joe Russo: "Murder herself."
 * Chris Hewitt: "Yeah, murder herself."
 * Joe Russo: "Yes."
 * Chris Hewitt: "And then she doesn't disappear, which is..."
 * Joe Russo: "That's correct."
 * Chris Hewitt: "... something that might have happened in other movies."
 * Joe Russo: "As Tony Stark says, it's..."
 * Chris Hewitt: "Yeah."
 * Joe Russo: "... "That's not how it works.""
 * Chris Hewitt: ""That's not how it works"! How much - how crazy did you drive yourselves with charts and wall charts and..."
 * Joe Russo: "Well..."
 * Chris Hewitt: "... all..."
 * Joe Russo: "... you..."
 * Chris Hewitt: "... sorts of..."
 * Joe Russo: "... you really do have to define..."
 * Anthony Russo: "Very interesting..."
 * Joe Russo: "Yeah."
 * Anthony Russo: "... question, yeah."
 * Joe Russo: "We had some..."
 * Anthony Russo: "Crazy."
 * Joe Russo: "... physicists come in, and you really do have to define your rules. The tricky part is, is that you're going against, you know, 35, 40 years of TV and film..."
 * Anthony Russo: "Narrative convention."
 * Joe Russo: "... stories that are telling it different."
 * Chris Hewitt: "Yes."
 * Joe Russo: "That are playing by a different set of rules. That was certainly the most complicated part of it."
 * All standard discussion again about how this isn't just one timeline being rewritten, this doesn't work like Back to the Future.
 * No.

Christopher Markus and Stephen McFeely
No.
 * Dave Itzkoff: "It's crucial to your film that in your formulation of time travel, changes to the past don't alter our present. How did you decide this?"
 * Christopher Markus: "We looked at a lot of time-travel stories and went, it doesn't work that way."
 * Stephen McFeely: "It was by necessity. If you have six MacGuffins and every time you go back it changes something, you've got Biff's casino, exponentially. So we just couldn't do that."
 * So not every time you go back does it change something. However, while "something" could be referring to changing a piece of time, it is more likely in context that McFeely is referring to rewriting the main timeline, and how it's too difficult to have every tweak rewrite things in the main timeline.
 * Stephen McFeely: "We had physicists come in - more than one - who said, basically, "Back to the Future is [wrong].""
 * This, again, seems to be specifically about the idea of, "In going back, you would rewrite the one timeline."
 * No.
 * Erik Davis: "Let's start with the time travel. What was your approach?"
 * Stephen McFeely: "[...] So, then, we had to decide what kind of time travel rules we were using. We brought in a couple of physicists who, to a man, said, "I'm glad you brought me in, because I've always wanted to talk to people from Hollywood to say that you know I love Back to the Future as much as the next person, but we don't think that's how it would work." Which was also helpful for us because as you can imagine, every time we went back to one of... you know we have six different time heists in three or four different periods... if every time you went back you created a new Biff's Casino, for want of a better term, right? Another crack in the version of your timeline? We would never get out of the second act."
 * This is McFeely saying, as has been said throughout this, that you cannot rewrite the one timeline.
 * No.
 * Reuben Baron: "The writers revealed that Marvel brought in physicists to provide advice on the mechanics of time travel. The duo was happy to hear one physicist flat-out state, "Back to the Future is bulls**t!""
 * More standard "not Back to the Future rules" discussion.
 * No.
 * Stephen McFeely: "We brought a couple of physics professors in to talk about time travel and that kind..."
 * Chris Hewitt: "Oh wow."
 * Stephen McFeely: "... of stuff. Yeah."
 * Chris Hewitt: "And they were like...?"
 * Stephen McFeely: "They mostly said, I think we're quoting them, "Back to the Future ' s bulls**t.""
 * Chris laughs.
 * Stephen McFeely: "Right? So we go, "Oh really. OK good that's helpful because...""
 * Chris Hewitt: "Yeah..."
 * Stephen McFeely: "... maybe I'm getting around to your question..."
 * Chris Hewitt: "Yeah..."
 * Stephen McFeely: "You know, when you remove something from each of these - we have six MacGuffins."
 * Chris Hewitt: "Yeah, yeah."
 * Stephen McFeely: "If you were to decide that there's a ripple butterfly effect for every time you did that, you would have Biff's casino times..."
 * Chris Hewitt: "Oh god yeah."
 * Stephen McFeely: "... 6 times 6 or whatever, right? So that was not available to us. It would be so puzzling, you know, we couldn't keep all that straight."
 * Christopher Markus: "Avengers: Biff's Casino"."
 * Stephen McFeely: "... "Biff's Casino"."
 * Chris laughs.
 * This is all the standard discussion again of how it is not the rewriting of a singular timeline idea from Back to the Future.
 * No.
 * Stephen McFeely: "If you operated by Back to the Future rules, every time you went back, and came back, you would have a new Biff's casino, right? [...] So, you can imagine that if every time, a new universe was created, we would get nowhere and we wouldn't know how to solve any one because which one did what? It was not helpful to us and we were worried that maybe we couldn't even do this idea. But we brought legit physicists in, quantum physicists, who said, "It probably doesn't work that way as much as I love that movies, it probably works this way, if it works," 'cause again..."
 * Christopher Markus: "... Which it doesn't."
 * Stephen McFeely: "... it doesn't."
 * Standard "It's not like Back to the Future" statements.
 * No.
 * Stephen McFeely: "We had a couple physicists come in, because Chris' research found that some of these Collider-type experiments noted that at the quantum level the same particle can exist in two places at once. And we went, "Ah, that's awesome." Then when we brought those physicists in, they kind of said Back to the Future is bulls**t. They don't look at our existence as one singular timeline..."
 * Standard talk about Back to the Future.
 * No.
 * Stephen McFeely: "... which helps us, to be honest, because we had so many second-act missions to different times. If those created a ripple in the timeline, you'd have an exponential number of Biff's casinos. We needed a cleaner version of time travel, which meant we had to educate our audience to not assume a different version."
 * Again, just discussing how each individual change in the past does not ripple through and rewrite the singular timeline.
 * No.
 * Stephen McFeely: "Again, it's not Back to the Future rules, it's branch reality rules. This is not stepping on a butterfly that turns the world into Biff's casino. You can't alter your future by going back to the past."
 * Again, not Back to the Future butterfly effect rules.
 * No.
 * Christopher Markus: "It also, if you follow the Back to the Future rules, made solving the problem really pretty easy. Like you go back, just pluck one little stone out, stick it in your pocket - it never happened. And it encumbered upon us with thirty superheroes, and this many millions of dollars at stake, to make it a little more challenging. So, those rules did not work for us."
 * Standard "It's not like Back to the Future" discussion.
 * No.

Result
No debate: No, unless maybe with the physics-breaking Time Stone.

Is the Marvel's Agents of S.H.I.E.L.D. 2091 the future of the universe the agents were in when they left 2017, or were they taken to a separate universe's 2091?
Unknown.
 * Debatable: Same universe and timeline.
 * So, the answer is not held here.
 * Unknown.

Can a timeline be literally changed/rewritten?
In some way lessening its validity, but not fully preventing it from ever happening.
 * No debate: No, unless maybe with the physics-breaking Time Stone.
 * So, it cannot have been rewritten. The closest it can come is in some way lessening that future's validity.
 * In some way lessening its validity, but not fully preventing it from ever happening.

Jed Whedon (implication only)
In some way lessening its validity.
 * Natalie Abrams: "Is the driving force of this season whether they can actually prevent the destruction of Earth?"
 * Jed Whedon: "That would be interesting. Yeah, what we're seeing is a horrible future that no one wants to have exist, so the first problem is trying to repair it, but maybe there's a bigger question of "Does it ever need to happen?""
 * The agents are hopeful that it doesn't ever need to happen. This would suggest that when they are successful in The End, they are successful in that regard, somehow making sure it in some way doesn't happen.
 * In some way lessening its validity.

Marvel's Agents of S.H.I.E.L.D. (in-universe, the characters might be mistaken)
In some way still exists, but also in some way preventing it/lessening its validity.
 * Leo Fitz: "Oh, not the girl's bloody time machine again. It's impossible. You cannot change time. It's fixed."
 * Fitz reaffirms his stance on time being fixed and unchangeable.
 * Melinda May: "What if it's not? She's been right about everything else, and for us to even have a chance, you and Simmons have to design the machine."
 * The agents are eventually successful, which makes this comment relevant. It is unlikely that the agents were successful but in a completely different way, with the agents being successful, the writers clearly intend for this to be relevant, that May was right: Robin has been right about everything else, with her help, they managed to "change time", finding that time is not "fixed". So their success is through some sort of method of changing time, not just their universe being separate and having a different future.
 * Leo Fitz: "Oh, not the girl's bloody time machine again. It's impossible. You cannot change time. It's fixed."
 * Fitz reaffirms his stance on time being fixed and unchangeable.
 * Melinda May: "What if it's not? She's been right about everything else, and for us to even have a chance, you and Simmons have to design the machine."
 * "Change time" also suggest they are in some way making the dystopian timeline less valid after they carve the better future.
 * In some way preventing it from ever happening/lessening its validity.
 * Phil Coulson: "It'd be great if Robin could help us fill in the blanks here. Daisy, you knew her first. Maybe you can get through to her."
 * Daisy Johnson: "I can try."
 * Melinda May: "If she helps us get home, maybe none of this ever happens."
 * "None of this ever happens" implies, again, some sort of lessening the validity of this future, even though they are not rewriting the timeline.
 * In some way preventing it from ever happening/lessening its validity.
 * Phil Coulson: "For Robin's sake, we need to make sure this world never comes to be."
 * Again, "make sure this world never comes to be" implies that when they are successful in The End, they are in some way making the dystopian timeline less valid.
 * In some way preventing it from ever happening/lessening its validity.
 * Phil Coulson: "We don't even know you did this."
 * Daisy Johnson: "I was right in the epicenter."
 * Phil Coulson: "I won't let you sacrifice yourself because you're scared of what's to come."
 * Daisy Johnson: "What's to come is the end of everything."
 * Melinda May: "If you can change the future here, you can change it from back home."
 * May continues to have a less scientific, more hopeful stance, simply taking each event as her current present with an undetermined future. So, in 2091, they are affecting events ("changing" from a certain perspective), so from her perspective, they can just do the same when they're back in 2017.
 * In some way preventing it from ever happening/lessening its validity.
 * 2017 Elena Rodriguez: "Are you telling me to go back and change the world, or are you warning me that I can't?"
 * Again, "change", not just prevent in some other universe.
 * 2091 Elena Rodriguez: "You need to go. They're coming."
 * 2017 Elena Rodriguez: "No, not yet."
 * 2091 Elena Rodriguez: "I hope you travel a path to a world I've never seen. Now go."
 * They hold out a little hope still that maybe, just maybe, something can be done to change things.
 * In some way preventing it from ever happening/lessening its validity.
 * Alphonso Mackenzie: "You just lost both your arms. That's not nothing."
 * Elena Rodriguez: "But I didn't die."
 * Alphonso Mackenzie: "And the future we saw isn't guaranteed."
 * Mack believes that future is not guaranteed, for whatever reason - that they can change it, or they can prevent it, or something. He is optimistic, though his exact hope is not spelled out here.
 * In some way preventing it from ever happening/lessening its validity.
 * Robin shrugs.
 * Melinda May: "We are going to try to make sure that this future never happens, okay?"
 * "Never happens" would imply actually rewriting time, in the way Fitz has said you can't, as Avengers: Endgame establishes you can't, and as is further disproved by Deke's continued existence. That said, May and Mack take the least scientific stance of the group, and it's likely this is just the way she sees "changing" time, still making more sense under trying to change time in some fashion than purely preventing it from being just in this universe.
 * In some way preventing it from ever happening/lessening its validity.
 * Leo Fitz: "I started having my doubts. Maybe your hopeful nature is rubbing off on me."
 * The agents still discuss the possibility that maybe time is not "fixed", with the writers clearly planting all these mentions as factors towards the ultimate solution (not least since it is mentioned again after they succeed). Time is suggested to be changeable in a certain fashion.
 * In some way preventing it from ever happening/lessening its validity.
 * Glenn Talbot: "So, this is who all the fuss is about, huh? She can tell the future?"
 * Polly Hinton: "Sort of. She sees a lot, but it's all out of order."
 * Another discussion of Robin's powers being that she sees things from across the timeline, just out of order. Not that she can see other universes.
 * In some way preventing it from ever happening/lessening its validity.
 * Leo Fitz: "Hmm, I'm not sure you actually know what "multiverse" means."
 * Deke Shaw: "That every choice we make spins out a different timeline into the cosmos, and right now, there are infinite parallel universes."
 * The thing is, Charles and Robin Hinton's powers both involved looking specifically into the future, which doesn't line up with the idea of equally valid branches ahead. It suggests that there is a timeline. There has been a hint, as previously discussed, that Robin's powers might see potential spin-out points, but otherwise her mind jumps across the timeline, until she feels the shift in The End into a new one. This would align better with the idea of "changing" time in The End, or the Avengers' success in Avengers: Endgame, but if Deke is correct, that would mean some sort of disparity between types of branches, with a "main" line that somehow gets shifted in The End and other somehow less important ones. This does not particularly make sense scientifically, so it's possible instead that these other universes are more hypothetical universes that don't come to be unless people manage somehow to break through into them as they're burgeoning, so Deke would have the general gist correct, but not quite there. This would likely be the most satisfying fit to all the statements, especially since a problem with the idea of shifting a "main" line doesn't really make sense, as if you were looking at a diagram of a timeline and could highlight one line, and then the highlight shifts, the diagram would essentially have to be animated, the same way you can only properly draw a 4-D object through animation, except time is already one of the axes on the diagram, so an animation of how this changes would involve some incomprehensible fifth dimension for how time changes over the fifth dimension's unit. Then again, maybe when you're talking about "changing" time, looking at "how time changes over the fifth dimension's unit" is in fact relevant, and with the agents not understanding exactly how they did it, perhaps there is something in that - or the hypothetical line essentially going down the dystopian branch then circling back on itself and through the other branch. Another option is perhaps that these universes all exist and Robin sees the timeline going through the statistically most likely outcomes at each split point, but that returns you to the previously mentioned problems with a tree of lots of equally valid universes.
 * As well as this, if there are numerous branches, why would the White Monolith just send them to one of those futures? And if it didn't, if it send them to all sorts of futures, you would have many versions of the agents all going back in time to the same stem 2017. There must be some sort of idea where there is a future in some regard, and where that can change.
 * In some way lessening its validity.
 * Deke Shaw: "But I am proof that you can move between them."
 * Deke saying he is proof you can move between these universes implies that the 2017-2091 jump and the 2091-2017 jump were not jumps between universes, otherwise he wouldn't be different to the others. They would just all be proof, and the agents in particular since they would have travelled first - to get there in the first place. So, when Deke says that he is proof you can move between them, he must be referring to the significance of being in a timeline where you'll never be born, as that's the only difference. This would suggest, therefore, that he believes the timeline they are currently in is already no longer headed for dystopia, for his future, but that that's fine because the dystopia still exists elsewhere in the multiverse tree. If they were now on a new branch from some divergence point c. late 2017/early 2018 since they got back, as it would appear he believes, then that doesn't change anything for Fitz and Simmons (and the others), who were born before the divergence point. It changes for him, because it means the timeline he's headed from is no longer the one they're in. He's proof, essentially, that if you "change time" then someone who theoretically shouldn't exist will not blink away, i.e. that you can safely shift to a world where you don't exist, because it's literally a different world.
 * The thing is, Deke wouldn't need proof you can move between them, by which he seems to mean, as established, proof you can survive outside one you're supposed to exist in. That's not really a problem if you've already established a multiverse existing, as there's no reason you wouldn't still exist if the multiverse existed. It's what he's establishing in the first place, "it could be the multiverse theory (in which case, I'm fine)", and then saying "and I'm proof that then you'd be fine". That's implicit in the first part, and he's not trying to prove any point about how someone would be okay switching timelines if it were a multiverse - I'm sure Fitz would agree, if it were a multiverse, someone would be okay switching timelines. What Fitz isn't sure about is whether there's a multiverse in the first place. So the only way this makes sense is if Deke's using his continued existence as proof of his point, and phrasing it poorly. Essentially saying, "Right now, there are infinite parallel universes instead of one timeline, and I'm proof of that, because I'm still around despite us changing things (having in a sense moved between them)! Plus of course that would show that you can survive in a timeline where you'll never exist, if you were wondering if you would or you wouldn't."
 * Leo Fitz: "Or, you are proof that we are in one timeline, in a loop an infinite, intractable, unchangeable loop."
 * Deke saying he is proof is inaccurate, even if you make the necessary assumptions about what he meant. Fitz points this out, he's only proof if they have already switched hypothetical timelines, but there is no reason to assume they have, so his continued existence could easily just be proof they're in one timeline and won't change things, so he will still be born. Fitz helpfully is pointing out the flaws in Deke's comments, which have been explored above. It would seem that his flawed comments essentially boil down to the fact that he's all too sure he's correct about the multiverse and making (poorly phrased) comments as if that's established as fact. Robin declares the change in events in The End, so Deke is wrong about himself already being proof of surviving outside of your timeline, since he's still on course for his future. It would seem again, that Deke's comments are more just included to seed an idea that will eventually pay off rather than to be fact here and now.
 * In some way still exists.
 * Deke Shaw: "Which is great, because that definitely won't affect me at all. Look, it's not like I'm just gonna blink out of existence. I lived in one timeline, but now I live in this new one, and I think I'm gonna stay in the one with the sun and tacos and all that, because that's the multiverse, that's science."
 * This informed the above exploration of what Deke was seemingly trying to say about moving between universes, and how it's safe to shift into a world where you're not supposed to exist, because he believes (seemingly correctly) that you are literally shifting into a different world, not a new version of the world.
 * In some way still exists.
 * Robin Hinton: "Something's different."
 * As discussed earlier, it would also seem that there is some sense of a main timeline or a future you are headed for, and that shifting, suggesting there are not just equally valid branches in a tree, specifically headed for the dystopian branch until this point, like this branch has just been split from the other timeline and wasn't necessarily, at least from some perspective, always due to split from it. Now, theoretically, all the timelines should already exist from a fourth-dimensional perspective, always due to split at the certain points, just only from the characters' perspective do they "go back" and create them. But perhaps there's something in that, that while Robin exists somewhat outside of a three-dimensional existence, she is still experiencing the characters' perspective of the branch timelines not yet being created, or again, there's some sort of fifth-dimensional thing involved where time changes over the fifth dimension's unit.
 * In some way preventing it from ever happening/lessening its validity.
 * Jemma Simmons: "It's times like this I wish we didn't change the timeline."
 * What they did was "change the timeline", which goes back to the previous discussions about whether there is a specific guiding of "the timeline" into one path, more valid in some capacity than other paths. It also again is a discussion of how what they did was "change" things, not just make things turn out differently in their universe.
 * In some way preventing it from ever happening/lessening its validity.
 * Enoch: "I presume Atarah wants to know how you were able to travel through time so that we may go back and save our world."
 * Jemma Simmons: "It's not that simple."
 * Atarah: "You deny that you meddled with the course of events?"
 * Daisy Johnson: "No, but we don't make a point of helping people play with time that have been trying to kill us."
 * Jemma Simmons: "It's complicated, we don't actually know how we did it."
 * This is interesting, and would suggest that the discussion above of how the exact fashion in which the agents have "changed" time being left unclear is not missing something. The exact fashion is not entirely clear to the agents, but in some way they have "meddled with the course of events", suggesting in some way changing time, lessening the dystopian future's validity.
 * In some way preventing it from ever happening/lessening its validity.

Marvel's Agents of S.H.I.E.L.D. (factual)
In some way still exists.
 * Deke Shaw: "Fitz died. He died, and no one was gonna bother to, I don't know, send me a text?"
 * Alphonso Mackenzie: "It was complicated."
 * Deke Shaw: "Yeah, no kidding. Besides the fact that this completely proves my entire multiverse theory, 'cause I'm still here, there's a second Fitz!"
 * The show is telling us that Deke was right, there's a multiverse, and that's why he didn't blink out of existence. The 2091 he is from wasn't literally rewritten, the same as with Avengers: Endgame establishing you cannot rewrite a timeline.
 * In some way still exists.

Result
Debatable: It has to still exist in some fashion, but with the references to having "changed" time, it also would seem that that 2091 is in some way less valid, less accessible, that this new future is somehow the new more valid timeline.

Films (in-universe, the characters might be mistaken)
Yes.
 * Bruce Banner: "With all due respect, alright, I - I'm not sure the science really supports that."
 * The Ancient One conjures a magic timeline, with the six Infinity Stones circling it.
 * Ancient One: "The Infinity Stones create what you experience as the flow of time. Remove one of the stones..."
 * The Ancient One swipes the Time Stone from the line, and a black line splits from the magic timeline.
 * Ancient One: "... and that flow splits."
 * This is fairly self-explanatory. Remove a stone from its timeline and the timeline splits in two. You have a branch of two timelines.
 * Yes.
 * Smart Hulk: "And remember, you have to return the stones to the exact moment you got 'em or you're gonna open up a bunch of nasty alternative realities."
 * If Steve doesn't get them back to exactly where they were, it leaves a moment where a timeline is Infinity Stone-less and timelines will start branching. Hence a moment in the timeline without all six different Infinity Stones leads to a split in the timeline/reality.
 * Yes.

Christopher Markus and Stephen McFeely
Yes.
 * Erik Davis: "So people are asking... Does this mean an old Captain America was hanging out this whole time while another Captain America was saving the day?"
 * Christopher Markus: "That is our theory. We are not experts on time travel, but the Ancient One specifically states that when you take an Infinity Stone out of a timeline it creates a new timeline. So Steve going back and just being there would not create a new timeline. So I reject the "Steve is in an alternate reality" theory."
 * When you take a stone out, it creates an alternate timeline. If there were any doubt that that is what splitting the flow of time meant.
 * Yes.
 * Reuben Baron: "In regard to what the destruction of the Infinity Stones means for the timeline, the writers are divided: McFeely said there..."
 * Stephen McFeely: "... could be trouble going forward..."
 * Reuben Baron: "... in regard to stability, while Markus argued that..."
 * Christopher Markus: "... the atoms are still there..."
 * Reuben Baron: "... so technically the stones' essence is still keeping time flowing normally.
 * The writers again raise the idea that the Infinity Stones are keeping the flow of time intact.
 * Yes.

Result
No debate: Yes.

Films (in-universe, the characters might be mistaken)

 * James Rhodes: "If we can do this - you know, go back in time - why don't we just find baby Thanos, you know, and...?"
 * Rhodes mimes choking baby Thanos.
 * Smart Hulk: "First of all, that's horrible..."
 * James Rhodes: "It's Thanos!"
 * Smart Hulk: "... And secondly, time doesn't work that way. Changing the past doesn't change the future."
 * Also interestingly about the fact he says "changing the past" and not "visiting the past", Bruce is already confident you can change the past. This could be because he already knows that the Infinity Stones are involved in meddling with time and so they'll be capable of changing things, but the way he and Nebula agree and the scene is done feels more like, "These guys are more scientifically knowledgeable so they know about changing the past." This would imply that you are capable of changing time anyway.
 * Leans toward yes.

Result
Debatable: Seemingly yes.

Can anything other than removing an Infinity Stone split the timeline?
It's possible.
 * Debatable: Seemingly yes.
 * So, decisions creating timeline splits is not out of the question.
 * It's possible.

Joe Russo
Unclear.
 * Joe Russo: "Every decision you made in the past could potentially create a new timeline."
 * This is a strange comment. None of the discussion has been about whether decisions create a new timeline. This implies that the act itself of going back didn't create the timelines, but rather that when they arrive, they have to work in compliance with the original timeline or else a decision they make could split the timeline. This would mean that not every jump necessarily created a new timeline. However, in Avengers: Endgame, those characters after arriving in the past have to jump back - if their decisions after arrival were what split the timeline, then what happened in the main timeline to the versions of them who didn't make that decision? They can't have jumped back to 2023 because then we'd have several versions of the characters arriving through the Quantum Tunnel simultaneously following the Time Heist. But it's highly unlikely that there's several versions of the characters out there in hiding having been left behind by the Time Heist...
 * What's more likely, if you were to take this interpretation, is that the jump itself didn't create a new timeline, but the landing of the jump, the arrival in that time, was a decision that split the timeline in each situation where there was a split, so in the normal timeline nobody was ever there in, say, 2012. This would mean that 2012 and 2014, where events are very much incompatible with the original timeline, had decisions split them. But the 1940s, 1970, 2013, and 2018 would be less clear, as they are potentially compatible with the main timeline.
 * However, this comment is different from everything else in the main discussion, I'm not sure it warrants too much thought. It's quite possible Joe Russo just meant that every decision you made in the past could potentially make your new timeline very different - that something like 1970, for example, would technically still be a new timeline but negligible from the main timeline so he's not considering it a proper "new timeline", but decisions in 2012 and 2014, for example, are proper "new timeline"s.
 * Joe Russo: "Every decision you made in the past could potentially create a new timeline."
 * Tying this into Marvel's Agents of S.H.I.E.L.D. (which he is not referring to), this could contribute for an explanation as to how the agents broke out of the loop - that in travelling back to the past, while this did not itself split the timeline, the fact that they had travelled through time essentially gave them the opportunity, somehow, to break away from the loop if their decisions made this happen.
 * Leaning toward yes.
 * Reporter: "Joe Russo pointed to two explanations of time travel in the MCU, one from Banner and the other from the Ancient One. Every action the heroes commit while in the past would result in the formation of a divergent timeline, or alternate reality, as a sort of butterfly effect."
 * This should not be read too much into since it's the reporter relaying what was said in their own terms and not a direct quote. The wording about "every action" forming a divergent timeline if taken very strictly would be what Joe Russo casually mentioned in the previous interview about actions creating timelines, but it is more likely that the reporter is just talking about Joe Russo discussing the heroes' actions going to the past creating divergent timelines.
 * Unclear.
 * Joe Russo: "And anything you do in that time shift would create a multiverse reality. It will create a new future, but it's not going to affect your past."
 * Here, Joe is saying that any action once shifted into the past creates a multiverse reality new future. This goes again slightly into the idea of it being actions that split the timeline and not their arrival, but them just being there is likely what he means.
 * Unclear.
 * Joe Russo: "Loki, when he teleports away with the Time Stone, would create his own timeline."
 * He means the Space Stone.
 * This again appears to be Joe Russo implying that an action is what creates a new timeline, though it might be just poor wording and he means either that at that point the timeline is properly different from the normal timeline or that at that point the timeline is not correctable, whatever he means by "correct".
 * Maybe, possibly just makes them distinct.
 * Joe Russo: "The minute that Loki does something as dramatic as take the Space Stone, he creates a branched reality."
 * Joe again makes a muddled comment about it just being actions that create a branched reality, while also suggesting that time in some way relies on "dramatic" actions. Again, this only makes some sense if you understand him to mean either that only at that point is the branched reality actually no longer negligibly different, or that it only at that point is unable to corrected/rectified in whatever sense that's supposed to mean.
 * Maybe, possibly just makes them distinct.

Result
Unclear: Unclear, possible.

Films (in-universe, the characters might be mistaken)
"Changing the past" exists, but not directly as rewriting time.
 * James Rhodes: "If we can do this - you know, go back in time - why don't we just find baby Thanos, you know, and...?"
 * Rhodes mimes choking baby Thanos.
 * Smart Hulk: "First of all, that's horrible..."
 * James Rhodes: "It's Thanos!"
 * Smart Hulk: "... And secondly, time doesn't work that way. Changing the past doesn't change the future."
 * It's interesting that he says "changing the past", not "visiting the past". It implies that time can be changed if you go back in time, not just visited in a causal loop/bootstrap paradox. However, when you make a change it doesn't impact this timeline, for whatever reason.
 * Something that does not affect the timeline you're from.

Joe Russo
It can involve creating alternate realities.
 * Joe Russo: "The time travel in this movie created an alternate reality."
 * Yes, this sounds like Joe Russo saying that all the time travel points are in one alternate reality, which doesn't make sense, but I wouldn't over-analyse this - it'll be the translation and he just means, "The time travel in this movie created alternate realities."
 * It can be the creation of alternate realities.

Stephen McFeely
It can involve creating alternate realities.
 * Stephen McFeely: "So for us the strongest thing we could do, and the most helpful thing we could do, is to operate under some kind of branch reality, so that the things that have already happened... which is what... again, it's time travel which is humanly impossible, but a number of physicists had told us it's much more likely we would operate in a branch reality than a singular timeline. So that's the floor for the time travel conversation."
 * The main plot functions under branch realities, not a singular timeline. He is referring to not rewriting the singular timeline.
 * It can be the creation of branch realities.
 * Stephen McFeely: "So we decided the branch reality one was better for us in that the reality you're in always happens, you cannot alter that. If you died you died, it is what it is. But it doesn't mean that you can't go back and, you know..."
 * Chris Hewitt: "Yeah."
 * Stephen McFeely: "... heist your stones."
 * Chris Hewitt: "Heist your stones and make things branch off in..."
 * Stephen McFeely: "That's right."
 * Chris Hewitt: "... in different directions..."
 * Stephen McFeely: "That's right."
 * This is an uncontroversial statement, just saying that the timeline is unchangeable but it is possible to go back and create branch realities when heisting Infinity Stones.
 * It can be the creation of branch realities.
 * Stephen McFeely: "So the idea of branch realities, of quantum travel..."
 * Branch realities are involved, which is not contested.
 * It can be the creation of branch realities.

Result
No debate: It should not involve rewriting any actual part of the timeline, seemingly only being the creation of an alternate reality in some fashion.

Is the timeline's future rewritten in Marvel's Agents of S.H.I.E.L.D.: Season 5 or does that 2091 still exist in some manner?
They didn't erase that future but may have devalued it somehow.
 * Debatable: It has to still exist in some fashion, but with the references to having "changed" time, it also would seem that that 2091 is in some way less valid, less accessible, that this new future is somehow the new more valid timeline.
 * The 2091 still exists in some manner.
 * They didn't erase that future but may have devalued it somehow.

Can a timeline be literally changed/rewritten?
With the discussing that time can be changed, it would seem that they achieved whatever the next best thing is to rewriting the timeline, without rewriting the timeline.
 * No debate: No, unless maybe with the physics-breaking Time Stone.
 * Not literally rewriting the timeline.
 * With the discussing that time can be changed, it would seem that they achieved whatever the next best thing is to rewriting the timeline, without rewriting the timeline.

Is it possible for decisions to create timeline splits?
Possibly through a branch timeline in which a different decision was made.
 * Unclear: Unclear, possible.
 * Maybe, so this might be involved in how they succeeded.
 * Possibly through a branch timeline in which a different decision was made.

What is "changing time"?
With the discussing that time can be changed, it would seem that they achieved whatever the next best thing is to rewriting the timeline, some sort of alternate reality perhaps of higher validity.
 * No debate: It should not involve rewriting any actual part of the timeline, seemingly only being the creation of an alternate reality in some fashion.
 * Not literally rewriting the timeline, presumably creating some sort of alternate reality.
 * With the discussing that time can be changed, it would seem that they achieved whatever the next best thing is to rewriting the timeline, some sort of alternate reality perhaps of higher validity.

Marvel's Agents of S.H.I.E.L.D. (in-universe, the characters might be mistaken)
Some sort of branch timeline forging a new universe.
 * Phil Coulson: "Yeah. And in that future, Earth is gone, and the last of humanity is enslaved by alien overlords. [...] There's a young Inhuman who's seen a better future. We're working toward that."
 * It would seem that the timeline should split in the future. For Robin to be able to see glimpses of changes other than the actual future she properly sees and connects with, these changes should also be in the future of this universe (splitting off).
 * Some sort of branch.
 * Glenn Talbot: "Who is this? And when does this happen?"
 * Polly Hinton: "That's not really how it works."
 * Robin Hinton: "Soon."
 * Glenn Talbot: "Soon... And these? These all come true? We need to act on this."
 * Everything Robin says comes true, the timeline of their universe still will be dystopian. The only way it isn't would therefore be if they, later than this, somehow split off into another timeline.
 * Some sort of branch.
 * Deke Shaw: "... But not according to the multiverse theory."
 * To be clear, we don't see the preceding part of the conversation. The scene starts mid-conversation.
 * Leo Fitz: "Hmm, I'm not sure you actually know what "multiverse" means."
 * Deke Shaw: "That every choice we make spins out a different timeline into the cosmos, and right now, there are infinite parallel universes."
 * It would seem that Deke's essentially saying, "Okay, I agree with you, you can't rewrite the timeline, but that doesn't mean we're stuck - what if, instead, the multiverse theory is true and we manage to forge a different future, not negating the past one but nonetheless positive."
 * With his previous comment no longer relevant, Deke nonetheless sticks to the idea of a multiverse. The show later goes on to suggest that Deke is correct, and therefore this statement is important. It would suggest that the show's stance on the multiverse is simply that all decisions spin out different timelines, and that this is what the multiverse is. Further, that would imply that when the agents manage to "change time", they are essentially at one of these spinning out points, and manage to guide their lives down the good path, and not toward the dystopian.
 * The nature of them guiding their lives down the good path, however, is unclear. If the multiverse tree is simply just that - a tree - on which one future is dystopian and one is not, then that would suggest that technically, the agents haven't changed things, just the show is choosing to instead follow into that good path, rather than the bad path, which it has otherwise been following when showing events post-2018. However, does raise a question of what extent to which the agents are exactly "successful", the same as with the Avengers and the fourteen million alternate futures. This way around would mean that they are not successful in any particular regard, just that the show and films are choosing to show us the one path where all the decisions went the certain way that was positive, while there's simultaneously many paths where everything ended up horrible. The only way to frame this positively is "But we're following the agents/Avengers who still had to make those sacrifices and the hard decisions. Just because there was always going to be a universe where things turned out OK and we happen to be following it doesn't mean that, from the people in that universe's perspective, they haven't faced the hardships to make their world this way. And if there's just infinite universes spinning off all the time, we essentially shouldn't worry about the ones we're not shown." That's not particularly satisfying though. While it's more acceptable for the agents (despite the comments that they are hoping to make sure this world "never comes to be"), who have at least given the dystopian branch universe some hope with Flint and Tess and done everything they can, while also needing that universe to still exist in some capacity for Deke to exist, it very much lessens the Avengers' victory. Plus, the whole idea of Strange going forward in time is to try to, in whatever capacity, guide things down the good route, not just go, "Well, it's out of her hands now. There will be a universe where things turn out well, and fourteen million, six hundred and four where they don't," and it would be odd for those things to also still play out exactly the same way with Strange having already seen them - if Strange were seeing futures in which he has just been looking at these futures. The Russos' comment about this later on helps.
 * Not literally rewriting time, but forging a new universe in some way.
 * Deke Shaw: "Which is great, because that definitely won't affect me at all. Look, it's not like I'm just gonna blink out of existence. I lived in one timeline, but now I live in this new one, and I think I'm gonna stay in the one with the sun and tacos and all that, because that's the multiverse, that's science."
 * Deke referring to living in "one timeline" is a little murky, as what he says would imply he just means "section of time", saying he prefers 2018 to the 2091 he's from. But in the wider context of the conversation, and the fact that he says "I'm gonna stay in" this one, it would imply that he believes this one is not headed for dystopia, so the "timeline" thing does probably specifically refer to a timeline and not just a section in time. This would align with, and further support, the idea that he believes they have already shifted into a new branch (as discussed, he seemingly doesn't believe he time-travelled between universes, just has since shifted into a universe different to the one he's from). As discussed, Robin in The End would suggest he is slightly mistaken, but nonetheless has the right idea.
 * Leo Fitz: "Or you're a canary in a coal mine."
 * Deke Shaw: "I don't know what either of those things are."
 * Leo Fitz: "We won't know if we're successful at changing the future unless you blink out of existence."
 * Jemma Simmons: "Fitz..."
 * Leo Fitz: "Jemma agrees. She actually wrote a paper on the theory of -"
 * Jemma Simmons: "Nobody knows how it works."
 * Right now, before the actual destruction of Earth which would obviously show them whether they're successful, if Deke blinked out of existence then they would know that they have successfully changed the future, at least a little - that they've broken out of the time loop (and must be in a universe of just one singular timeline that gets rewritten). If Deke doesn't blink out of existence, as far as they know they might have already changed the future, but by the multiverse theory - so are in a new branch, but they would have no way of knowing. So only if Deke blinks away can they be sure they're successfully changing the future, for now.
 * Some sort of new timeline from a point in 2018.
 * Piper: "Prepare to be the first S.H.I.E.L.D. team in space."
 * Alphonso Mackenzie: "In this timeline, maybe."
 * This comment is confusing. Is it supposed to imply that there's another timeline where some other S.H.I.E.L.D. team got there before they did? Because there's nothing suggesting that at any point. I think it might just be Mack getting generally hopeful about multiple timelines.
 * Unclear.
 * Robin Hinton: "Something's different."
 * Robin feels the shift at this point, implying she's been still seeing the dystopian future up until this point but the team have now gone off into a divergent timeline just now. It also, as discussed earlier, would mean that it's a timeline split at this point, and definitely not that this was always going to be the future of this universe.
 * Some sort of branch.
 * Jemma Simmons: "He'll be a little disoriented. But he'll be so happy to know that time is not fixed. It's a fluid, ever-changing, beautiful thing."
 * The agents have found time is "not fixed", "ever-changing". They have in some capacity changed time, not just forged their individual universe, always an entirely separate universe from the dystopian one, a better future than the dystopian one. They have changed events and found time to be fluid, and the way the show presents is that no, you cannot rewrite events, but the next best thing is "spinning off" the universe the way Deke explained, however they did that exactly.
 * Almost changing time, the next best thing, however that is defined.
 * Matt Webb Mitovich: "The Fitz that Coulson hopes Simmons "finds" one day - that's the one who froze himself inside Enoch's ship in the other timeline?"
 * Maurissa Tancharoen: "Yes."
 * The question is poorly phrased, as regardless of theory, the Fitz they are currently hoping to find did not freeze himself in another timeline, he just froze himself 6 months ago. It can be assumed that the interviewer in fact means "the one who froze himself and in the other timeline was inside Enoch's ship for 74 years". So, with Maurissa Tancharoen's confirmation, it would also suggest a split in the timeline is the intention (with it being the same Fitz who froze himself, just not the same one at this point to the one who was still frozen in the other timeline) rather than always separate universes (which would mean it isn't at all the same Fitz).
 * Maurissa Tancharoen: "He's on his way to save them."
 * Jed Whedon: "He went the long way, so [he and Enoch are] still traveling."
 * He went the long way to save them, implying it's the same man who, in one timeline, arrived to save them after going the long way. And now, in this timeline, they can go and get him while he's still travelling. It's not an entirely different Fitz, just the same Fitz sent in a different direction from May 2018 on.
 * They split the timeline in some way.
 * Leo Fitz: "I'm very, very, very much alive."
 * Deke Shaw: "Yeah, and you look great, by the way. Younger, an-... or something. I haven't really done the math on that - but I will, 'cause it's your brain that I inherited! Oh, and I - I, uh, I - I don't wanna gloat, because technically the argument was with the other you, but, uh, you know, you being here, you prove that my multiverse theory was right, so..."
 * The fact that Fitz can be here, rather than stuck out in space, proves Deke's point that he made to the other Fitz about how multiple timelines exist, spinning out into the cosmos - his multiverse theory. If there were only one timeline, he would be stuck out in space, unless they had actually rewritten that timeline, which is impossible and also would mean Deke wasn't here with them.
 * Some sort of branch.

Result
Debatable: '''They could not erase the 2091 from ever existing, as rewriting time is not possible. However, due to the multiverse's existence, so the possibility to in some way spin out a new timeline from a decision being made a different way, a new universe was forged from a point in May 2018 during The End, and it would seem that, with this considered changing time and not just making time 50 : 50 good : bad, that in some way did shift the idea of a main "time" down the other trouser, in some way making the dystopian future less valid. How they did this is not meant to be fully clear, with the agents themselves not entirely sure, but it might involve something to do with time-travellers essentially being in some way volatile in their place in the timeline, and their decisions therefore capable of causing a breakaway universe if they manage to turn things down a burgeoning potential universe with a different decision. It does not seem that this is just one of infinite branches, but that Deke Shaw's comment was more about something slightly different to do with the multiverse that maybe holds within it a nugget for how exactly one splits a universe with decisions.'''

Can anything other than removing an Infinity Stone split the timeline?

 * Debatable: Seemingly yes.
 * It is likely possible that Infinity Stones are not the only things splitting the timeline.
 * It is likely possible that Infinity Stones are not the only things splitting the timeline in Avengers: Endgame.

Films (in-universe, the characters might be mistaken)
Leans toward yes.
 * Bruce Banner: "With all due respect, alright, I - I'm not sure the science really supports that."
 * The Ancient One conjures a magic timeline, with the six Infinity Stones circling it.
 * Ancient One: "The Infinity Stones create what you experience as the flow of time. Remove one of the stones..."
 * The Ancient One swipes the Time Stone from the line, and a black line splits from the magic timeline.
 * Ancient One: "... and that flow splits."
 * It is not stated that this is the only way the flow can split, though it is implied considering alternate timelines are crucial to the film and this is the only time their creation is mentioned.
 * If this is not the only way the flow can split, then it is possible that they are already in a branch timeline, and are then causing that timeline to split - so a branch on a branch, potentially meaning that the erasing brought up later is just erasing bad branches on the already-existing branches, and not just erasing the whole branch from the main timeline.
 * Infinity Stones being the only way in this film to create new timelines would make scientific sense, since travelling through time alone should only keep you in a causal loop - if you travel back to 2012, then in 2012, you were there. The Infinity Stones, a wholly fictional construct with the power to manipulate the flow of time as the Ancient One explains, would make sense as a way to break this.
 * The Ancient One doesn't actually refer to time travel, so why would removing an Infinity Stone specifically be the only "time travel rules"? Well, if Infinity Stones are the only things causing timeline splits, that doesn't mean they're the only time travel rules. The rules would still be there, just be "you can't really change time", and then the Infinity Stones are just a rule in general which happens to, in this instance, pertain to time travel since it is the method through which the Infinity Stones would be removed from the timeline.
 * Ancient One: "Now this may benefit your reality, but my new one, not so much."
 * The orange line is Bruce's reality, the main reality as we call it. But in removing a stone, he leaves behind that dark "new" reality with the Ancient One in it, and it causes her problems.
 * If this were just a split on what is already a branch, then that would mean Bruce's reality is not the orange line, it's neither line. Granted she doesn't say the orange line is Bruce's, but it's implied. More important is her saying "my new one", implying that she, as she is speaking to Bruce, will be left behind in a dark timeline, and not that she will be split into two timelines, with one version in the okay timeline and just one not. This implies that removing the stone will not cause a further branch than the branch already happening, she will be stuck in the bad timeline, so since the removal of the Stone does split the timeline, that branch being something already happening would mean the split should be because of the stone, and not a split from arrival and a further split from the stone, as there's only one split.
 * Leans toward yes.

Christopher Markus and Stephen McFeely
Yes.
 * Erik Davis: "So people are asking... Does this mean an old Captain America was hanging out this whole time while another Captain America was saving the day?"
 * Christopher Markus: "That is our theory. We are not experts on time travel, but the Ancient One specifically states that when you take an Infinity Stone out of a timeline it creates a new timeline. So Steve going back and just being there would not create a new timeline. So I reject the "Steve is in an alternate reality" theory."
 * Here, Markus specifically highlights a line the Russos have not acknowledged. When you take a stone out, it creates an alternate timeline. Markus doesn't specify that that's the only way, but the italicizing in the report of the "Infinity Stone" and him then saying "So Steve going back and just being there would not create a new timeline" does imply he is saying that Infinity Stones are the only way to create a new timeline.
 * Yes.
 * Christopher Markus: "We had to boil our time rules down to something, and it came down to the stones, the stones are going to hold the universe in place. Take 'em out, things start happening."
 * Markus is saying that the time rules in Avengers: Endgame relate to the Infinity Stones, and the fact that the "time rules" "boil [...] down" to this very much implies the time rules relate solely to the Infinity Stones. And then if you take them out, things start happening to time.
 * Christopher Markus: "And, again, this is the pleasure of having this universe to deal with, we needed someone to explain it. Who's the most entertaining explainer in the Marvel universe? Let's get Tilda!"
 * Markus is saying that this is what was explained in the Ancient One scene.
 * Leans toward yes.
 * Stephen McFeely: "We sort of created our own time travel rules wherein, as the Ancient One says, if you remove an Infinity Stone from a timeline, that creates a branch reality."
 * McFeely lays this out as the rules they established. Simply that removing an Infinity Stone from a timeline creates a branch, no other reason.
 * Leans toward yes.
 * Audience member: "What are the rules?"
 * Christopher Markus: ""What are the rules?" So glad you asked that. In the movie, the rules are basically: If you - you can go back, you can do whatever you want, it won't affect the future. Unless you take out an Infinity Stone, then it branches."
 * Markus refers again to nothing affecting time unless you remove an Infinity Stone.
 * Yes.

Anthony and Joe Russo
Leans toward no.
 * Joe Russo: "But what's interesting about it - and you know people may... savvy people may come to ask how old Cap is in this timeline at the end of the movie."
 * This comment would suggest that, since the discussion of how Infinity Stones split the timeline would mean that if you pay attention there is an explanation in the film for why Steve would be there, that discussion would not mean that Steve would not create a divergent timeline.
 * Chris Hewitt: "Yeah.... that is one of my questions."
 * Joe Russo: "That... that is an interesting story, isn't it?"
 * Chris laughs.
 * Anthony Russo: "Joe just brought up a question that we're not going to answer..."
 * Chris laughs.
 * Anthony Russo: "... interesting!"
 * Joe Russo: "That could be a..."
 * Chris Hewitt: "Okay."
 * Joe Russo: "... story for another time."
 * Anthony Russo: "Yeah."
 * Chris Hewitt: "Okay, interesting."
 * Joe Russo: "But, look..."
 * Chris Hewitt: "Should I ask it? Should I even just go - I'll go there and then you can do what - "How is old Cap in this timeline at the end of the movie?""
 * Joe Russo: "Well it's something that will be explained..."
 * Anthony Russo: "There's..."
 * Joe Russo: "... perhaps at some point."
 * Anthony Russo: "There's clearly, you know, in order for you to - in order for that to be, according to the rules of the movie that we set out, there's some missing story that, obviously that we're not getting in the film. We don't really want to delve into that missing story. I mean, the great thing about the MCU is, like, anything that doesn't show up on screen, anything that doesn't become text, is fodder for future storytelling."
 * The explanation that only removing Infinity Stones creates branches, so Steve didn't create a branch, would in fact be something explained within the film, implying that's not the explanation.
 * Leans toward no.

Result
Debatable: Leaning toward yes, but possibly no.

Films (in-universe, the characters might be mistaken)
No.
 * Tony Stark: "Quantum fluctuation messes with the Planck scale, which then triggers the Deutsch proposition. Can we agree on that?"
 * The dissection of this quote can be found under July 20, 2019, the Time Travel in the Quantum Realm San Diego Comic-Con 2019 panel.
 * Dissected later.
 * Smart Hulk: "Which can't now be changed by your new future."
 * "New future" is interesting: As in it's literally a new future that has been changed, or just this is your "new future" because time is realigned from your perspective in the way Smart Hulk just laid out about how the past becomes your future? Either way though doesn't particularly matter because if it's the latter, it's just a continuation of what he's been saying about the adjustment of 2023 now being in your past etc., and if it's the former then he's saying that when you have changed time, you are now in a new timeline - something that is not disputed. It's what can allow you to change time/cause a new timeline that's in question.
 * The only problem with not clearly knowing which way Hulk means by "new future" is that, if he is referring to a literal new future of an alternate timeline, then, while the conversation is still predicated on changing time nonetheless, he does in his explanation say "If you travel to the past", as if that were what would happen regardless, not just in the scenario of someone changing time. In that case, Hulk could be seen to be saying that if you travel to the past, you create an alternate timeline. But there's several assumptions involved there and ultimately, it's not possible to know what Hulk means - he seems to just be talking about a shift in perspective, anyway. This scene appears to more just be about establishing the "You can't rewrite time" rule than the rules of creating alternate realities.
 * Indeed, Banner's comments about how the main timeline can't be changed by your new future apply in either sense. "Because you are just in the timeline, in a time loop" or "Because you aren't in that timeline anymore".
 * Maybe yes, maybe no - because maybe he's talking about alternate timelines or just being in the timeline, and because maybe it's just predicated on already changing time and maybe it's not.
 * Ancient One: "If I give up the Time Stone to help your reality I'm dooming my own."
 * Either they are already in different realities or she's saying that it would create a different reality if she gave up the Time Stone, and thus doom her reality that he's leaving behind.
 * Maybe yes, maybe no.
 * Bruce replaces the Time Stone, and the black line disappears.
 * Bruce Banner: "... it never left."
 * As explained, there is a problem with the idea that removing an Infinity Stone would somehow split the timeline only from the point in time when it is removed. As well as suggesting some sort of making everything since arrival into an alternate timeline, this also goes against the idea of the timeline already splitting on arrival, since it would require the timeline to somehow split again on that branch, which does not seem plausible.
 * Seemingly no.
 * Smart Hulk: "And remember, you have to return the stones to the exact moment you got 'em or you're gonna open up a bunch of nasty alternative realities."
 * This should mean Steve does not create realities by travelling back. If every time you travel back you create a new timeline from where you arrive, then Steve would create a branch on every branch he's visiting, meaning he's just creating a new okay timeline but nonetheless leaving behind a nasty alternative reality.
 * It shouldn't create a branch.

Christopher Markus and Stephen McFeely
No.
 * Christopher Markus: "Basically said what the Hulk says in that scene, which is, if you go to the past, then the present becomes your past and the past becomes your future. So there's absolutely no reason it would change."
 * If you go to the past, say 2012, then 2023 is now in your personal past while 2012-2023 is now your future. And then he says that there's absolutely no reason why that would change because your past is now ahead of you to be lived through, seemingly describing a causal loop. Markus would therefore be suggesting that Hulk is not referring to alternate timelines when he says this, just that you can't directly change the past.
 * Leaning toward no.
 * Erik Davis: "Let's start with the time travel. What was your approach?"
 * Stephen McFeely: "[...] So, then, we had to decide what kind of time travel rules we were using. We brought in a couple of physicists who, to a man, said, "I'm glad you brought me in, because I've always wanted to talk to people from Hollywood to say that you know I love Back to the Future as much as the next person, but we don't think that's how it would work." Which was also helpful for us because as you can imagine, every time we went back to one of... you know we have six different time heists in three or four different periods... if every time you went back you created a new Biff's Casino, for want of a better term, right? Another crack in the version of your timeline? We would never get out of the second act."
 * Adding that not "every time you went back" would you create "another crack in the version of your timeline" is interesting, potentially suggesting that not every jump creates a split, though in context it's likely just the way he is talking about rewriting the timeline.
 * Leaning toward no.
 * Stephen McFeely: "... they much more embrace a branch reality version of time travel..."
 * Specifically referring to the "version of time travel" as "branch reality" implies that the jumps in time themselves create branches.
 * Leaning toward yes.
 * Audience member: "What are the rules?"
 * Christopher Markus: ""What are the rules?" So glad you asked that. In the movie, the rules are basically: If you - you can go back, you can do whatever you want, it won't affect the future. Unless you take out an Infinity Stone, then it branches."
 * This comment seems to confirm that the intention of the Hulk statement was not to discuss branching timelines, just that you can't change the timeline, with the Ancient One statement then being the part about branches.
 * No.

Anthony and Joe Russo
Yes.
 * Joe Russo: "... it's just like what Hulk said, what happened in the past has already happened. If you go back to past, you simply created a new reality."
 * Joe says that if you go back to the past, you simply create a new reality, which would mean that every jump into the past creates a split in the timeline, though in context, he is just talking about Avengers: Endgame so likely just Quantum Realm travel. This causes a problem with the returning of the stones, because it would mean you cannot just revisit certain points in the past.
 * It's unclear if, by the time he gets to "If you go back to the past, you simply created a new reality", he is still referring to "what Hulk said" or has moved on, because Hulk did not clearly refer to alternate realities unless you try to read into his comments to make it sound like alternate realities.
 * Joe Russo: "The characters in this movie created new timelines when they went back to the past, but it had no effect to the prime universe. What happened in the past 22 movies was still canon."
 * This part alone does not necessarily mean that every jump to the past created new timelines, only that at least some did. But with the parts above, it would imply it's every jump.
 * Yes.
 * Joe Russo: "Both Ancient One and Hulk were right. You can't change the future by simply going back to past. But it's possible to create a different alternate future."
 * Saying "it's possible" would imply that it doesn't always happen, which would support that not every jump in time creates a split. However, he is saying, "It is impossible to change the future by simply going back to the past, however you create a different alternate future," so it's likely that the reason he says "possible" is simply as a synonym for "however" in counter to the talking about changing the future being "impossible", not so much to imply that it's possible to not create a different alternate future.
 * Unclear.
 * Reporter: "Joe Russo pointed to two explanations of time travel in the MCU, one from Banner and the other from the Ancient One. Every action the heroes commit while in the past would result in the formation of a divergent timeline, or alternate reality, as a sort of butterfly effect."
 * If the reporter actually means Joe Russo discussed the heroes' actions going to the past creating divergent timelines, then this would refer to the Time Heist (the actions the heroes commit much more likely meaning that than anything like Steve's choice) and not Clint and Steve.
 * Unclear.
 * Anthony Russo: "All you can do by going to the past - and for a character like Cap[tain America], living in the past - is create an alternate future. So this is a world in which alternate timelines exist."
 * In the context of just being about this film, Anthony is making a comment about creating alternate timelines. Now, he doesn't say that you can't stay in a time loop, only that the only way of altering time is that you "can" "create an alternate future". But he adds that Captain America created an alternate future, which is the main example of where it would be in a time loop.
 * Not necessarily, but quite possibly.
 * Sonaiya Kelley: "Was it difficult presenting a theory of time travel that hadn't previously been explored onscreen?"
 * Anthony Russo: "Back to the Future is one of our favorite films, and the rules of that movie are ubiquitous; they have informed pop culture for 40 years. And we wanted to do something different. We didn't realize how complicated it would be to create new rules and have people go with us, but we learned very early on in the test screenings that people are really committed to those Back to the Future rules - if you shoot yourself, you should die. We spoke with a few physicists, and there's a lot of theories about how time travel could work. We chose the multiverse theory."
 * The fact that "the multiverse theory" is described as their method of time travel would imply that time travel in the film is always multiverse-related, i.e. their decision is that time travel creates alternate universes full stop, as in every time. But there's definitely flexibility in this part of the comment for it to just mean that the multiverse theory is their choice over rewriting a singular timeline, not that multiverse is the only way time travel works ever in Avengers: Endgame.
 * Leaning toward yes.
 * Joe Russo: "And anything you do in that time shift would create a multiverse reality. It will create a new future, but it's not going to affect your past."
 * Assuming Joe just means that them just being there is enough to create that multiverse reality, this would mean that on arrival you would create a new timeline.
 * Leaning toward yes.
 * Joe Russo: "But that is what's most interesting. You've seen everything else, everything else about being looped in time or whatever, you've seen it all. What's really interesting is that you create multiple timelines and it's said in the movie twice."
 * Hulk doesn't explicitly talk about alternate timelines. He says you can't change a timeline and then mentions a "new future" in relation to talking about changing time, which can be interpreted as either a new future from your perspective, since, say, 2012-2023 is now in your future and not your past, or literally a new future. Joe's comment here would imply it's the latter, for that scene to also be about alternate timelines. However, Joe doesn't here say that every jump is a timeline, just that during the Avengers' time travel they've created multiple timelines.
 * Leaning toward yes.
 * Joe Russo: "What happens is you then create a new future by going into the past."
 * This comment implies that simply the act of going to the past creates a new timeline, regardless of other factors like Infinity Stone removal.
 * Leaning toward yes.
 * Joe Russo: "So, by necessity, by logic, you then create - if you were to stay back there - you would create an alternate timeline."
 * Joe seems to feel that if you went back to the past, because you cannot change the timeline, you would have to create an alternate timeline by necessity. The comment about it being if you stay there is unclear, because there is no particular reason why the timeline would wait a while and then go, "Okay, now I'll split." He doesn't acknowledge the possibility of going back in time and not changing time by doing that.
 * Unclear, leaning toward yes.
 * Jessica Shaw: What... he's in an alternate reality so this is not like a Ray Bradbury situation?
 * Joe Russo: "Well so, so what happens is we're playing with a different form of time travel, it's the multiverse notion of time travel."
 * Describing specifically the method of time travel as "the multiverse notion" implies that the whole time travel is working by splitting into the multiverse, rather than it just being one element of the time travel in the film.
 * Leaning toward yes.
 * Joe Russo: "So if you go to the past the only thing you can do is create an alternate future, right?"
 * The word "can" here somewhat implies that it doesn't necessarily always happen. If you go to the past, the only thing you can do to affect time is create an alternate timeline. But that doesn't rule out someone going back in time and just not affecting time. Still, in context, Joe Russo appears to just mean "what does happen is...".
 * Joe Russo: "That's what Cap does, is, there's an alternate future that happens, so, he would live out that life with Peggy in an alternate future, and he would have to then get back to this timeline to hand off that shield [...] You can imagine, in your own head, another Cap story taking place in that alternate timeline."
 * Even if there were some leniency in Joe's previous comment, the only reason leniency is being sought for is due to Cap's story, and he specifies that Cap did live in an alternate future.
 * Leaning toward yes.
 * Joe Russo: "The time travel rules that we're playing with are that, you know, that you can create a time branch which... you know, sort of an alternate timeline based on interruption of a timeline."
 * Here, Joe only says that you "can" create a branch, not that that is always the case.
 * Not necessarily, but quite possibly.
 * u/Reggie_48: "Can you help me/everyone understand how Captain America got back to the main timeline when he returned all the stones, because it contradicts the time travel theory stated by Banner earlier in the movie. Banner said that when you go back in time you make a separate timeline, so it doesn't [affect] the past, but if Captain America was in a different timeline when he returned the stones, how did he [get] back to the main timeline without the use of the quantum suits[?]"
 * I've corrected the spelling and grammar through this message to make it easier to read.
 * This user incorrectly states what Banner says. Banner never said that if you go back in time you make a separate timeline. He said you can't change the past, and that if you are in the already process of changing past events then you're still not changing the past. The implication of his statement is then that either it's just not possible to change past events, or that if it is, you would be in an alternate timeline, he doesn't specify. But either way, it's only if you are changing things, and not just jumping back in time.
 * Russo brothers: "You are correct in that he would have had to have worn the quantum suit, using a Pym particle to make the jump."
 * The Russos seem to implicitly suggest it's correct that if you go back in time, you make a separate timeline.
 * Leaning toward yes.

Eric Michelsen
Possibly yes.
 * Eric Michelsen: "Deutsch is a believer in the "multi-worlds" interpretation of quantum mechanics which says that the universe is actually splitting into, sort of, very-similar-but-not-quite-exactly-the-same duplicate parallel universes, and in that model with certain ideas from quantum mechanics, what you'd find is that energy is conserved on average over all the universes, but not specifically and individually in every universe."
 * This suggests that when Tony talks about triggering the Deutsch proposition, he is referring to split universes.
 * Possibly yes.

Result
Debatable: '''The films and Markus and McFeely suggest no, while the Russos suggest yes. Scientist Eric Michelsen's comment would seemingly slightly support the Russos, but the films and writers together have more weight, especially with the massive problem of returning the stones if the timeline splits - so it would seem that no, merely arriving does not split the timeline. But there is definitely uncertainty.'''

Does removing an Infinity Stone split the timeline?
Maybe, maybe not.
 * No debate: Yes.
 * Removing an Infinity Stone splits the timeline, regardless of if anything else does. So, at the very least, we have a split for 2012, 2013, 2014, and 1970. It is quite possible that there is a split on a split in 2012 and 2014, when the second stone from each (Mind and Soul) is taken, depending on the exact nature of the way things split - if it is just that the removal of an Infinity Stone solidifies the time since arrival as an alternate timeline, there might not be a further split. However, it might solidify it as an alternate timeline while also still then splitting again, or the arrival alone made it an alternate timeline and the Infinity Stones are splits on the splits, so you would end up with a split on a split on a split in 2012 and 2014.
 * Maybe, maybe not.

Does merely arriving, after travelling back in time via the Quantum Realm, split the timeline?
If it turns out that arriving through time does split the timeline, yes. However it seems arriving through time doesn't, so it's unclear.
 * Debatable: The films and Markus and McFeely suggest no, while the Russos suggest yes. Scientist Eric Michelsen's comment would seemingly slightly support the Russos, but the films and writers together have more weight, especially with the massive problem of returning the stones if the timeline splits - so it would seem that no, merely arriving does not split the timeline. But there is definitely uncertainty.
 * If they did, then you would be looking at a split at the arrival points in 1970, 2012, 2013, and 2014, then a further split on 1970 when the Space Stone is taken, a further split on 2012 when the Time Stone is taken a further split on that branch when the Mind Stone is taken, a further split on 2013 when the Reality Stone is taken, and a further split on 2014 when the Power Stone is taken and a further split on that branch when the Mind Stone is taken.
 * If it turns out that arriving through time does split the timeline, then it would seem that the answer is yes. However it seems arriving through time doesn't, so it's unclear.

Christopher Markus
Yes.
 * Christopher Markus: "So, Steve only had to fix six... six paths."
 * Steve would be fixing six rather than six branches - just because the timeline's split already when the Power Stone or Time Stone are removed from the main timeline, shouldn't mean it doesn't split again when the Soul Stone and Mind Stone are removed respectively. So you would have, by this interpretation, four branches off the main timeline, and two of those branches would have a further branch several minutes later off of them.
 * A problem with this is the same as one of the ones previously discussed about the idea that arriving through time also splits the timeline. The removal of an Infinity Stone theoretically should indeed be somehow solidifying everything since arrival as a splinter timeline. In 2012 and 2014, you are already in an alternate timeline, definitely by this point because the Time and Power Stones are already gone. If the further removal of an Infinity Stone were to cause a further split, you would end up with Scott Lang and Clint Barton being present in that time, and then a split when they go back leaving a timeline without an Infinity Stone, and a timeline still with it. And again: except, how? The Avengers going back is what removes the stone from the timeline, so you would have to have the split occur, say, the moment they hit the button to return, so in one version of events they disappear and in one they do not. So, why? Does it just not work? Why wouldn't it? And in that case, you also end up with versions of Scott and Clint abandoned in time. This is not as problematic a notion as with the idea of arrival causing a split, because there you would be looking at - if timelines are erased - the other timeline being erased and not the one where they are stranded, though in this case both would be erased, if the timelines are erased, so that's less of a problem. Still though, it's a little bizarre. You could question whether perhaps, because it's not actually said that it would be one timeline with stones and one without, maybe both timelines are missing a stone. That solves your stranded Avengers problem, except it is shown that removing an Infinity Stone creates one dark branch of reality specifically dark because it's missing an Infinity Stone, not that it poisons both timelines. Now, in this branch-on-a-branch situation, both would be missing Infinity Stones anyway, but it still implies that the way removing an Infinity Stone works is that you have one timeline with as many as before and one offshoot with minus one. That said, this is a different scenario to the one that Smart Hulk and the Ancient One are discussing, which is an initial removal from a complete set, one which it seems quite possibly makes everything since arrival an alternate timeline, so then just removing another one could function slightly differently, just further splitting the flow of time indiscriminately. After all, if the removal of an initial stone makes everything sine arrival an alternate timeline - which this point otherwise suggests, as discussed above - then you do have a problem: that would mean the further removal of an Infinity Stone theoretically would make no further difference, yet also it seems that removing another Infinity Stone would further break the flow of time. The idea of it just splitting further, not particularly where one result has more Infinity Stones than the other, serves as a compromise. So, this point would suggest that the initial removal of an Infinity Stone makes everything since arrival an alternate timeline, as previously discussed, and then is not necessarily a big problem with the idea of further splits in 2012 and 2014.
 * Markus says six branches, one for each Infinity Stone, which means that in whatever fashion, 2012 and 2014 split further after an initial split.

Result
Debatable: It would seem that the answer is that, in whatever fashion, yes, there is a further split in 2012 and 2014.

Does removing an Infinity Stone split the timeline?
At least four.
 * No debate: Yes.
 * Yes, so at least four splits.
 * At least four.

Can anything other than removing an Infinity Stone split the timeline?
Not necessarily only four/six.
 * Debatable: Seemingly yes.
 * It's possible for there to be other reasons for splits than just the Infinity Stones.
 * Not necessarily only four/six.

Does merely arriving, after travelling back in time via the Quantum Realm, split the timeline?
If it turns out that arriving through time does split the timeline, you end up with likely ten branches. However it seems arriving through time doesn't, so more likely just four or six.
 * Debatable: The films and Markus and McFeely suggest no, while the Russos suggest yes. Scientist Eric Michelsen's comment would seemingly slightly support the Russos, but the films and writers together have more weight, especially with the massive problem of returning the stones if the timeline splits - so it would seem that no, merely arriving does not split the timeline. But there is definitely uncertainty.
 * If they did, then you would be looking at a split at the arrival points in 1970, 2012, 2013, and 2014, then a further split on 1970 when the Space Stone is taken, a further split on 2012 when the Time Stone is taken a further split on that branch when the Mind Stone is taken, a further split on 2013 when the Reality Stone is taken, and a further split on 2014 when the Power Stone is taken and a further split on that branch when the Mind Stone is taken.
 * You would end up with, aside from the main timeline: 1970 with Space Stone, 1970 without Space Stone, 2012 with Time and Mind Stones, 2012 without Time Stone, 2012 without Time and Space Stones, 2013 with Reality Stone, 2013 without Reality Stone, 2014 with Power and Soul Stones, 2014 without Power Stone, and 2014 without Power and Soul Stones.
 * If it turns out that arriving through time does split the timeline, you end up with likely ten branches. However it seems arriving through time doesn't, so more likely just four or six.

Does the removing of the Mind and Soul Stones, after the Time and Power Stones have already been removed respectively, cause a split on a split?
If it turns out that arriving through time does split the timeline, you end up with likely ten branches. However it seems arriving through time doesn't, so more likely just six - but not four.
 * Debatable: It would seem that the answer is that, in whatever fashion, yes, there is a further split in 2012 and 2014.
 * This would mean that, depending on whether the timeline splits on arrival or not, you have six or ten branches, not four.
 * Ten if the timeline splits on arrival, but if not, as it seems, just six - but not four.

Christopher Markus
Six, with wiggle room for more.
 * Christopher Markus: "So, Steve only had to fix six... six paths."
 * The implication is that there are six paths in total, each of which Steve is fixing in whatever manner - not that Steve is only fixing six of the paths. However, there is wiggle room in the statement for that to be the case if necessary.
 * At least six. Seemingly just six, though wiggle room for more if necessary.

Result
Debatable: '''It would be six rather than four, with further splits in 2012 and 2014. So at least six. With arriving via the Quantum Realm seemingly not splitting the timeline and Markus' comment, seemingly just six. If arriving via the Quantum Realm is found to, in fact, split the timeline, then it would seem there are, in fact, ten branches, but it would seem like just six.'''

Joe Russo
Steve is correcting/rectifying them, which might not mean erasing, possibly just putting them on the right course.
 * Travis Clark: "At the end, when Cap brings the stones back in time, does he correct all the timelines that got screwed up? Is there a past Loki still out there?"
 * Joe Russo: "The intent was that he was going to correct the past timelines at the point that the stones left."
 * "Correct"? It's unclear exactly what this would mean, it doesn't seem to be the same as erasing, but Joe doesn't clarify what correcting is.
 * Steve is correcting them, which might not mean erasing, possibly just putting them on the right course.
 * Joe Russo: "It gets very complicated, but it would be impossible for [Cap] to rectify the timeline unless he found Loki."
 * If Steve is only rectifying them, it's odd that, if this is the intention in the film, they talk about how they'll clip all the branches, if they know they can't.
 * Steve is rectifying them, which might not mean erasing, possibly just putting them on the right course.

Result
Debatable: Steve is correcting/rectifying them, but the exact nature of this is unclear.

What is Steve doing when he returns the stones?
Unclear.
 * Debatable: Steve is correcting/rectifying them, but the exact nature of this is unclear.
 * It could be that he is erasing them, it could be that he is just setting them on a better course.
 * Unclear.

Films (in-universe, the characters might be mistaken)
Yes.
 * Ancient One: "So tell me doctor, can your science prevent all that?"
 * Bruce Banner: "No... but we can erase it."
 * They cannot prevent the suffering that would happen by removing the stone. However, they can erase the suffering from existence.
 * Leaning toward yes.
 * Bruce replaces the Time Stone, and the black line disappears.
 * Bruce Banner: "... it never left."
 * The black line disappearing is interesting. They are "eras[ing]" the suffering from existence rather than preventing it. Returning the stones to their time but the timelines continuing would mean they are merely preventing it. The black line dissipates, it disappears, it's erased. Returning the stones has to in some way erase some dark splinter timeline.
 * A way of fudging this comment, if you want to accept that the branches continue, is to take it that they are still in fact preventing the suffering, but in a different manner. That the Ancient One is asking, "What, are you going to fly around to all these places and stop all the suffering that would be caused?" ("prevent" suffering practically), and Bruce is responding, "No, we'll just stop the suffering from ever happening" ("erase" the suffering from ever having to happen, which is still preventing but can, in a sense, be seen as erasing). But this still does not align with the black splinter line dissipating.
 * Bruce saying "that reality" refers to the Ancient One talking about "this new branch of reality". So when he says in that reality it never left, accompanied with the dark line disappearing, he is seemingly essentially saying, "In that reality it never left, so that reality actually in the end doesn't ever exist." The dialogue on its own can be taken to mean, "In that new reality, it at least still always has an Infinity Stone," still meaning there's a new reality, just it's not Infinity Stone-less - but in conjunction with the timeline diagram, it's got to be erased, otherwise it would just be the dark line becoming orange as well.
 * Yes.
 * Steve Rogers: "Don't worry Bruce... clip all the branches."
 * So he's getting rid of branches. He's clipping them. He's not just rectifying them. This matches the fact that Bruce specifically says that you cannot prevent the suffering, but can "erase" it.
 * Yes.

Christopher Markus and Stephen McFeely
Yes.
 * Stephen McFeely: "We think Steve went back, put all the stones back, clipped those branches. Those are fine."
 * McFeely says that Steve "clipped" the branches, like the film. This would imply cutting off certain branches, through erasing or simply slicing off in some form. However, "Those are fine" is more ambiguous, as it could fit with the idea more of just fixing each branch, putting things on the right course.
 * Leaning toward yes.
 * Stephen McFeely: "Which was actually probably unnecessary if you take the stone because you're going to erase that time - that branch where he doesn't have it anyway."
 * McFeely touches on the erasing of the timelines, something mentioned in the film but rarely touched on in interviews. McFeely here says that Steve would be erasing that time when he returns the Reality Stone. There is a slight wiggle room here, to take it as, instead of meaning "You're going to erase that time anyway", rather "You're going to erase that time - the branch where he doesn't have it, anyway", as in "well, at least that branch", and exploiting that to mean that it's a branch on a branch that Steve is erasing, the branch from 2013 still existing. But that's clearly not the intention, the intention is that Steve is erasing the 2013 branch after returning Mjolnir.
 * Yes.

Result
No debate: Yes.

Christopher Markus and Stephen McFeely
While most of what they said would imply there is, albeit while joking, the final comment is much more explicit, said at a later date, and not joking. It seems that no, there is not a leftover timeline without Mjolnir and the Reality Stone.
 * Dave Itzkoff: "Thor recovers his hammer, Mjolnir, by taking it from an earlier timeline. So that raises the question - "
 * Stephen McFeely: "Does that screw that other Thor?"
 * Christopher Markus: "Is he killed by Dark Elves?"
 * McFeely saying this implies there's precedent for there being some other Thor without Mjolnir now. But Steve returned Mjolnir with the Reality Stone, said to erase the bad timeline without the Reality Stone (and Mjolnir), regardless of whether that's the only branch in 2013 or whether it's a branch on a branch - there should be no Mjolnir-less timeline. This comment would suggest that the timelines created still exist, even the stone-less ones regardless of whether they are the only branch timelines or branches on branches. This fits with a major problem with the "every jump in time creates a branch" point of view, because in that case Steve would only create a new, nicer timeline at the point of each return and not do anything to rectify the timeline missing an Infinity Stone. But that idea flies in the fact of the film. Ultimately, it's important to note that they are joking through this part of the interview.
 * Leaning toward yes.
 * Christopher Markus: "You can make any number of what ifs. The Dark Elves would have arrived, intending to get the Aether. It's what they came for and it was no longer there."
 * This again implies that the Reality Stone-less timeline continues to exist, despite what the film says - unless this is interpreted as them discussing what might have happened if that timeline had continued to exist.
 * Stephen McFeely: "So they build a paradise together."
 * Christopher Markus: "They all got married."
 * Laughter.
 * Again, worth noting that they're joking throughout this Thor: The Dark World part, so it's perhaps not worth putting too much weight into.
 * Leaning toward yes.
 * Chris Hewitt: "... which is really interesting. And, you know, things go wrong occasionally in these time heists. The person I feel sorriest for in this movie, and there are some major, major deaths, is the Thor whose Asgard is about to be..."
 * Stephen McFeely: "Hamerless!"
 * Chris Hewitt: "... ransacked..."
 * Christopher Markus: "Yes."
 * Chris Hewitt: "... by Dark Elves, and he has no hammer because big Thor has just gone and taken his..."
 * Stephen McFeely: "This..."
 * Christopher Markus: "But..."
 * Stephen McFeely: "... is true...."
 * Christopher Markus: "... the Aether is also gone, so theoretically the Elves, who I think can detect the Aether, should go..."
 * Chris Hewitt: ""Eh!""
 * Christopher Markus: "... "Eh," and just turn around."
 * Chris Hewitt: "They would just pass by."
 * This part is odd as it implies that the Reality Stone and Mjolnir-less 2013 timeline still exists. This would align with a problem with the Russo explanation - that if every jump creates an alternate timeline, there is no way of going back and correcting (or erasing) the timelines. But it doesn't align with either parties' intentions, that no timelines be left behind without Infinity Stones, to fall into chaos. They are joking here, and also perhaps speculating about the hypothetical future of that timeline until Steve comes back and corrects or erases it, but it's an odd conversation.
 * Leaning toward yes.
 * Jeff Goldsmith: "What would you tell the people asking about where Thor's hammer, Mjolnir, is?"
 * Stephen McFeely: "I think he brought it back to Asgard."
 * Christopher Markus: "He gave it back to the Thor of that time."
 * This aligns with the film more than the jokey comment before about a timeline where Thor is "hammerless". It can, therefore, be taken that that comment was indeed just a joke and this is the intention. So, according to the writers, Steve returned Mjolnir to that Thor.
 * Leaning toward no.

Result
Debatable: Seemingly no.

Films (in-universe, the characters might be mistaken)
It could lead to disaster.
 * Steve Rogers: "Don't worry Bruce... clip all the branches."
 * The fact that he's clipping all the branches would imply that he's erasing all the branches which could otherwise potentially have been nasty, not just erasing the nasty branches and leaving some others. This was part of Bruce's promise to the Ancient One.
 * If the timelines are not all erased, there is a problem with the possibility that the Avengers have just started a disastrous, innumerable chain of timelines. After all, at least the 1970 and 2013 timelines almost certainly have Thanos' Snap in their future - the changes will not have affected that. The insignificant changes they caused would mean an eventuality where, almost certainly, they hit 2023 and have the exact same idea for the Time Heist. They then go back and would cause splinter timelines themselves from 1970, 2012, and 2013, some of those from which you would again end up with a Time Heist, causing further splinters off those. Granted, the 2013 timeline's 2023 Avengers who go back to 2013 would find things slightly different, with main timeline Thor present in that 2013, but the ones going to 1970 would still cause a normal splinter timeline, with that 1970 still different. You could cause a countless number of disastrous chains, and if those chains do have an end, many of them would only be ending because the Avengers don't have the Time Heist idea in the same way (after all, they had a one in fourteen million chance in the main timeline, one significant change and there's a good chance they don't succeed), so could also have doomed innumerable timelines to tragedy in saving their own. They would have started an uncontrollable catastrophic mess, especially hard to believe with Bruce's insistence that they're going to put everything right and keep it under control.
 * It could lead to disaster.

Stephen McFeely
The timelines it seems would be as close as possible to the original timeline, but it's possible that this is not a relevant comment, especially since it's been established that they didn't mean that there was a timeline left behind without Mjolnir and the Reality Stone.
 * Stephen McFeely: "I think we're leaning on, when you just take a baseball mitt, you didn't ruin that kid's life. When you took Mjolnir, we accept that that movie happened. Because time is irrefutable."
 * The second part resembles a discussion from X-Men: Days of Future Past: "Now there's a theory in quantum physics that time is immutable. It's like a river, you can throw a pebble into it, create a ripple, but the current always corrects itself. No matter what you do, the river just keeps flowing in the same direction." McFeely seems to be implying that this timeline would play out similarly without Mjolnir, despite the brief difference in events.
 * The different way of interpreting what he says - that he is just talking about that Thor: The Dark World still happened in the main timeline as it was because time cannot be changed - would instead suggest that this comment has nothing to do with what would happen in that possibly continuing timeline.
 * The timelines it seems would be as close as possible to the original timeline, but it's possible that this is not a relevant comment, especially since it's been established that they didn't mean that there was a timeline left behind without Mjolnir and the Reality Stone.

Result
Debatable: '''The timelines would quite possibly end up as similar as possible to the main timeline. Even if that McFeely comment isn't relevant, 1970 and 2013 would almost certainly end up pretty much the same anyway, and that could end in a disastrous chain.'''

Are any branches erased?
Possibly.
 * No debate: Yes.
 * At least some branches are erased, so it seems Steve has to be erasing some things at least, not just rectifying.
 * Possibly.

Is there a timeline without Mjolnir and the Reality Stone?
Possibly.
 * Debatable: Seemingly no.
 * It would seem that there at least none of the Time Heist timelines are either lacking Infinity Stones anymore or if there were ones where the Infinity Stones were taken then those have been erased.
 * Possibly.

What would happen to the timelines if they were left behind?
Hopefully.
 * Debatable: The timelines would quite possibly end up as similar as possible to the main timeline. Even if that McFeely comment isn't relevant, 1970 and 2013 would almost certainly end up pretty much the same anyway, and that could end in a disastrous chain.
 * The timelines have a huge potential for disaster if left behind, so, especially with Bruce's assurance to the Ancient One, it would seem that all of them should be erased.
 * Hopefully.

Films (in-universe, the characters might be mistaken)
Yes.
 * Smart Hulk: "And remember, you have to return the stones to the exact moment you got 'em or you're gonna open up a bunch of nasty alternative realities."
 * This quote begs the question: Would he be opening up specifically nasty realities (as in when he puts back the stones he's making sure that that there are specifically no nasty alternative realities, not that there are no alternative realities whatsoever), or just opening up realities, which could be nasty (he's making sure no realities which are nasty are left behind, just okay ones)?
 * Unclear.
 * Steve Rogers: "Don't worry Bruce... clip all the branches."
 * The fact that he's clipping all the branches would imply that he's erasing all the branches which could otherwise potentially have been nasty, not just erasing the nasty branches and leaving some others. This was part of Bruce's promise to the Ancient One.
 * If Steve makes sure there is never a point where the stones aren't a complete set, then technically, should there therefore never be any alternate timelines created at all, when there must be for events to play out differently? If they are entirely prevented from coming into existence, then they never existed to visit. An explanation for this could tie into Christopher Markus' unclear comment about being able to do whatever you like without fear for the main timeline changing, and the Clifford V. Johnson comment about stitching the universe differently. Their interference is not an actual alternate timeline, more of an aside like the Dormammu loop, but the problem is that then they remove an Infinity Stone which causes a proper split in the timeline. However, this does not particularly fit with the Steve explanation. More likely, it can be taken that the timelines just collapse at the point the stones are returned (the same moment they're taken). The removal of the Infinity Stones still in some way had an effect, despite the returning at the exact same moment - it allowed for branch timelines. But the branch timelines then collapse at the moment of return.
 * Yes.

Anthony and Joe Russo
No. 2012 at least persists, but this relies on the idea that Steve is rectifying timelines rather than erasing them.
 * Reporter: "... to ensure the trillions of lives in each of the divergent realities would be spared from the Avengers' tampering and continue to exist."
 * This would be them preventing the suffering, not erasing it, like Banner promised. It's just making the divergent timeline nicer because it does still have an Infinity Stone. This Russo explanation would mean that the black line shouldn't disappear, just turn orange. The only ways to reconcile this with the film are the thing I mentioned during the dissection of the Ancient One scene where you essentially ignore the black line demonstration and take a certain interpretation of Banner's words, or if you assume that the Infinity Stone-less timeline is only a branch on the branch already created by the time travel. Thus by replacing the stones you are still erasing the suffering rather than preventing it, by erasing that split, but this also doesn't strictly adhere to this comment, as it would essentially mean that you go from 50 : 50 of the two branches on the branch with good : bad to just one timeline existing, the good one. You aren't actually sparing those people in the bad split from the Avengers' tampering, you're just stopping those people affected by the tampering from existing. There's no real way to make this comment work.
 * Leaning toward no.
 * Sonaiya Kelley: "Since Loki vanishes with the Tesseract, could he still be alive in the new timeline or would Cap returning the stones undo that?"
 * Anthony Russo: "Loki could absolutely still be alive in an alternate timeline."
 * So according to this, the Avengers did not in fact manage to keep their promise and get rid of any timeline damage? This comment would imply that a) the timeline still exists, and b) has substantial changes which the Avengers have not rectified.
 * No.
 * Joe Russo: "It gets very complicated, but it would be impossible for [Cap] to rectify the timeline unless he found Loki."
 * This implies that Steve is essentially trying to make every timeline be as unchanged as possible, not erasing the timelines as said in the film.
 * This would mean that the 2012 timeline in some way persists. The Russos' comments would imply all the timelines persist, just rectified in some way, but at the very least this would imply the 2012 timeline persists.
 * No. 2012 at least persists.
 * Anthony Russo: "We're dealing with this idea of multiverses and branched realities, so there are many realities."
 * This would suggest the realities are still around.
 * Leaning toward no.
 * Joe Russo: "Our interpretation of that is a multiverse, which we just think is a lot of story potential."
 * This implies that the timelines are still around as part of the universe.
 * Leaning toward no.

Christopher Markus and Stephen McFeely
Leaning toward yes.
 * Christopher Markus: "And dead is dead, and Loki's dead, except for in that one past reality, which I think has been erased, I don't know."
 * Markus brings up the idea of erasing the timelines which has been ignored in many interviews. He does seem to believe that Steve would be erasing these timelines (specifically 2012, one of the very disrupted ones, implying all of the timeliens would be erased), however the way he speaks seems to line up with other implications from the writers that there is grey area intentionally left in the film over how the branch timelines work out, and also that they are not in the loop on what Marvel want to do next - that they might exploit the grey areas and take things in certain directions.
 * Leaning toward yes.
 * Jeff Goldsmith: "Did you ever decide that there was maybe a moment you were gonna get into the multiverse?"
 * Stephen McFeely: "It clearly exists, right? Because Doctor Strange has talked all about it. I mean that's, it's part of the fabric of that. We may not - this may be where I disagree with Marvel or where they're going, I have no idea where Kevin Feige is going, I don't know what's happening tomorrow, I have no idea."
 * Christopher Markus: "Are you okay?"
 * Stephen McFeely: "But I'm a big believer in stakes, and if you tell me that I can just go and get another Natasha and another Tony and we can keep rolling, then particularly my grandma is gonna go, "Well why did I watch that?" So yeah we are retraining the audience all the time. There may be - I may be wrong 2 years from now where people want, "I want all sorts of stories from people I already lost.""
 * Christopher Markus: "Well particularly in a movie where we are very much heading towards some final resolutions, toward things ending, toward people leaving. If you go, "Yeah but there's seventy-five Tonys out there, like seventy-five billion Tonys out there," your drama is gonna suffer."
 * They seem to suggest that the time travel did not contribute to the multiverse, which could refer to the idea of erasing the timelines.
 * Leaning toward yes.
 * Jeff Goldsmith: "Did you map out where Loki goes after he grabs the Tesseract in 2012?"
 * Stephen McFeely: "TBD."
 * Christopher Markus: "Probably to cause some havoc in Asgard."
 * Stephen McFeely: "It's probably mischief."
 * Jeff Goldsmith: "But if he has escaped a branched timeline before it was destroyed, would that inspire a new movie that reconciles what Loki does with the Tesseract?"
 * Stephen McFeely: "Listen, we don't work at Marvel, man. I don't know."
 * Goldsmith takes the branch being "destroyed" as a given from their conversation and McFeely does not refute this. It certainly seems that that is the writers' intention. Obviously, the show Loki is now happening following this Loki, but it would seem from McFeely that, by their time travel rules intention, Loki would have to escape that timeline before it is destroyed for the character to continue.
 * Leaning toward yes.
 * Christopher Markus: "And, so we had to rejigger them and luckily we have the Infinity Stones which seem to have their own rules, and so why didn't we just [...] lay some time travel rules on them, so we, as the Ancient One said, made it that you only create these branch realities when you remove an Infinity Stone from that time."
 * Markus says that the time travel rules are laid on the Infinity Stones, and then specifically that "you only create these branch realities when you remove an Infinity Stone from that time", very explicitly laying out that point-of-view, as well as confirming that's what the Ancient One was saying when they wrote it.
 * Leaning toward yes.
 * Christopher Markus: "So we could tighten up the possibilities. Because writing is all about just winnowing down the possibilities, the worst moment in any project is when you have too many options. And so, ideally, as time goes on, you're killing off options to get to one story. Which is why, people get exci- when people get excited about the multiverse, I just stare at them like, "Wha-? You can'- your stakes are gone!", like if, "Well, 1 inch over, there's a room where this didn't happen," it's like, "Well then why are we telling this story?" You know, "Oh, your dog died? Let's go over there and get your other dog from...", you know. So while it, you know, may be a fascinating idea, it's pretty hard on drama. But the time travel, on the whole, was actually great for drama, it turned out."
 * Markus implying they did not want to be creating a multiverse could refer to the erasing of the timelines.
 * Leaning toward yes.

Result
Debatable: '''The Russos are the only source leaning toward no. Overall, the most evidence suggests that yes, all the timelines are in some sense erased. There is a little chance though that they persist, 2012 being specifically mentioned.'''

Films (factual)
It was seemingly left intentionally open for exploitation.
 * Change of scene.
 * Steve Rogers: "You should be proud of yourself, Peggy."
 * Steve and Peggy look at photos of Peggy with her children, no husband.
 * The photos do not include a husband. There could be in-universe reasons for this: Peggy and her husband divorced some time after the 1953 interview, Peggy's husband passed away some time after the 1953 interview, or he simply was not present for the photos. If he passed away or was not present for the photos, it would still be strange that she chooses not to have a photo of him by her, alongside her children, but still. However, the reason, it would seem, was to leave the options open for who they ended up making her husband. The writers then claim that it was their intention to write Avengers: Endgame in such a way that indeed, Steve is the missing husband. This certainly makes sense here, with Peggy not including photos of her husband on her desk since her husband was kept mostly secret and lying low, to make sure no one works it out, and especially so Steve does not see it.
 * It was seemingly left intentionally open for exploitation.

Christopher Markus and Stephen McFeely
Yes, they wanted to exploit that missing information to make Steve the husband, and might even have semi-planned it all along, with that goal in mind.
 * Christopher Markus: "I do believe that there is simply a period in world history from about '48 to now where there are two Steve Rogers. And anyway, for a large chunk of that one of them is frozen in ice. So it's not like they'd be running into each other."
 * Steve returning to 1948 and living through this timeline would also make him Peggy's husband mentioned in Captain America: The Winter Soldier in an interview from 1953, tying up the loose end that Markus and McFeely have left in both Captain America: The Winter Soldier and Marvel's Agent Carter of who the mysterious husband was.
 * It doesn't hurt.
 * Christopher Markus: "... We like your idea."
 * Patrick Shanley: "Really? Alright."
 * Stephen McFeely: "It was our intention that he was always the father of those two children."
 * It might not have been their intention all along for Steve to be the husband, but it was at least their intention in this film for the gap to be exploited and that to be the case.
 * While it might not have been the plan all along, it's nonetheless significant since their intention was to exploit that missing information.
 * Stephen McFeely: "The husband that you very purposefully did not see at Peggy's bedside in Winter Soldier is Chris [Evans]' Steve. We have always thought that he was her husband."
 * McFeely makes it sound here more like it was always their intention to make it this way. It is possible that they intentionally left the husband out not just to leave options open but, by the sound of it, in the hope that they could find a way to make it so that Steve was always that husband. But this in particular makes it sound like this was the long game for the writers, very much establishing the idea of Steve being Peggy's husband and part of the main timeline as an intentional choice.
 * Yes, they wanted to exploit that missing information to make Steve the husband, and might even have semi-planned it all along, with that goal in mind.

Sean Carroll
It doesn't hurt.
 * Aylin Woodward: "I think in this case, I see no reason to doubt that [Cap's] in the same timeline. If I remember correctly, when Cap visits elderly Peggy in Captain America: The Winter Soldier, she doesn't say who she gets married to."
 * The point about hiding Peggy's husband all along does tie in with the writers' comments about exploiting that to intentionally make Steve the husband all along.
 * It doesn't hurt.

Result
No debate: Yes, the writers wanted to exploit that missing information to make Steve the husband, and might even have semi-planned it all along, with that goal in mind - regardless of whether that ends up working with the time travel rules.

Christopher Markus and Stephen McFeely
He lived a simple, stay-at-home life, hidden away, and changed his identity.
 * Erik Davis: "Do you think there's a world where we see the adventures of Captain and Peggy either on the big or small screen?"
 * Christopher Markus: "Possibly. I think maybe all I did was Steve was a stay-at-home dad and Peggy went to work at S.H.I.E.L.D.. I don't know that there were any adventures."
 * This would explain Steve being able to stay hidden for 75 years, and was the assumption I had personally made due to the film suggesting this was his retirement to live a "beautiful" quiet life.
 * He lived a simple, stay-at-home life, hidden away.
 * Stephen McFeely: "So, his younger self is on ice somewhere and it's only in 2011 that there are technically two Steves running around - to the point where if you were to look closely at Peggy's funeral, there'd be an old man in the back named Roger Stevens."
 * Steve would have changed his identity ("Roger Stevens" is a joke but indicates that he changed his identity) when living in the main timeline.
 * He changed his identity.

Result
No debate: If indeed he were in the main timeline all along, he lived a simple, stay-at-home life, hidden away, and changed his identity.

Joe Russo
Joe Russo doesn't mention it, but yes, there's clearly a problem.
 * Joe Russo: "The characters in this movie created new timelines when they went back to the past, but it had no effect to the prime universe. What happened in the past 22 movies was still canon."
 * If every jump into the past created a branch in time, it would be impossible to safely return the Infinity Stones. Steve would arrive at each point and just cause a split branch on the branch, one where he returned the Infinity Stone, still leaving behind a dark branch. This goes completely against Bruce saying that the science supports them being able to make sure there are no dark timelines, and the idea of returning the Infinity Stones, unless there is some way in which he could return them without physically arriving.
 * Joe Russo doesn't mention it, but yes, there's clearly a problem.

Result
Unclear: '''There's clearly a problem. Unclear if there's some solution.'''

Joe Russo
Either Steve didn't have to physically return them in those timelines and just had to essentially recomplete the set just at the split points, or it is in some way possible to navigate the timelines.
 * Steve Rogers: "Well, after I put the stones back..."
 * Steve did manage to put the Infinity Stones back, so the method works.
 * The only thing that is shown in the film is going back in time, and then being yanked back to where they left: main timeline, 2023. However, Steve returned the stones, which were taken from alternate timelines, so either he didn't have to physically return them in those timelines and just had to essentially recomplete the set just at the split points, or it is in some way possible to navigate the timelines.

Result
Unclear: Either Steve didn't have to physically return them in those timelines and just had to essentially recomplete the set just at the split points, or it is in some way possible to navigate the timelines.

Does the idea of returning the Infinity Stones cause a problem for the idea that every Quantum Realm jump into the past creates a branch timeline?
Should involve just jumping back without causing a branch.
 * Unclear: There's clearly a problem. Unclear if there's some solution.
 * Should involve just jumping back without causing a branch, otherwise you're not particularly fixing anything.
 * Should involve just jumping back without causing a branch.

Can you navigate the system of timelines through the Quantum Realm?

 * Unclear: Either Steve didn't have to physically return them in those timelines and just had to essentially recomplete the set just at the split points, or it is in some way possible to navigate the timelines.
 * Self-explanatory.
 * Either not returning them physically, just somehow replacing them to recomplete the set at the split points, or navigating the timelines to physically return each one.

Films (in-universe, the characters might be mistaken)
Somehow getting back to the rough time of the Time Heists and making it so that there is a complete set at all times.
 * Bruce Banner: "Because once we're done with the stones, we can return each one to its own timeline at the moment it was taken."
 * So each stone would be returned to each branch timeline. At the moment it was taken - presumably means the exact moment the Avengers disappear to return to 2023 with the stones in hand.
 * There is no precedent for being able to navigate the alternate timelines in the film, like travelling back to 2012 and then forward down the offshoot timeline to where the stone left, so it might be the case that the exact moment they got there would be some sort of volatile point where the branch timelines start to break away due to the Infinity Stones being removed from that bubble, and they're putting them back to eliminate the bubble from forming into a full timeline.
 * If it is not as simple as stopping a volatile point, you have to make assumptions about being able to navigate the branch timelines.
 * If Steve does literally have to return the stones within the locations, we should note that Bruce doesn't say the exact place. Steve presumably could, for example in 2014, show up nearby on Morag at the exact moment Rhodey leaves.
 * Somehow getting back to the rough time of the Time Heists.
 * Bruce replaces the Time Stone, and the black line disappears.
 * Bruce Banner: "... it never left."
 * The stone is always present in the timeline.
 * It would seem from the return journeys that it's okay to have two of the same stone present at once since Steve takes them all and drops them off one-by-one instead of returning for each.
 * Making it so that there is a complete set at all times.
 * Bruce replaces the Time Stone, and the black line disappears.
 * Bruce Banner: "... it never left."
 * It would seem that the timeline became volatile as they removed the stones, but in returning them there was never a moment where the stones were gone, so the timeline doesn't split. The leaving almost creates a dark splinter timeline, but it's erased by the returning of the stones.
 * Making it so that there is a complete set at all times.

Anthony and Joe Russo
Most evidence suggests (especially with the one against not being a direct quote) Steve has to physically arrive in the timelines.
 * Xiang Rong: "How would Cap react when he encounters Red Skull when he returned the stone?"
 * Joe Russo: "Red Skull would probably put the Soul Stone back to its location, and wait for the next unfortunate stone-seeker to make a sacrifice. Cap and Red Skull probably won't fight. It's because it's his mission to return the stone to its original place. The Red Skull is also no longer the same Red Skull from The First Avenger. He is more like a ghost, you could almost say he's a completely different entity now. He only exists to guard the stone, his past conscious may or may not exist anymore.
 * This implies that Captain America would indeed have to physically take the stone back to Red Skull to return it.
 * Steve has to physically arrive in the timeline and meet Red Skull.
 * Reporter: "With that in mind, the Ancient One warns Banner to return the Infinity Stones to their proper places in the main timeline..."
 * Returning them to their proper place in the "main timeline" again seems like a slight mis-wording from the reporter. It's not the main timeline when they're missing. But if it was actually what they said, this would support the idea that since they cannot seemingly navigate the timelines, they only have to return the stones to the volatile points in the main timeline where a timeline threatens to split out to stop them from splitting.
 * Maybe Steve just has to somehow get back to the split points in the main timeline to somehow recomplete the set there.
 * Joe Russo: "He would have to encounter Red Skull."
 * This again suggests Steve has to physically go and return all the stones.
 * Steve has to physically arrive in the timeline and meet Red Skull.
 * Joe Russo: "He would have certainly met Red Skull to return the stone."
 * Again, meaning Steve would have to physically return the stones to each place.
 * Steve has to physically arrive in the timeline and meet Red Skull.
 * u/Nirok: "How did the meeting between Cap and the Red Skull go when he returned the Soul Stone after [Avengers: ] Endgame? Is there a story there and will we ever see it in a future movie?"
 * Anthony Russo: "It was probably more awkward than you imagine it was. Red Skull felt slated because Cap didn't recognize him."
 * Again, a comment that Steve had to physically go and meet Red Skull to return the Soul Stone.
 * Steve has to physically arrive in the timeline and meet Red Skull.

Christopher Markus and Stephen McFeely
Steve probably has to physically arrive in the timelines.
 * Reuben Baron: "Fans probed about other loose ends, such as Loki's escape with the Space Stone following the Battle of New York. McFeely said the scene..."
 * Stephen McFeely: "... offered possibilities..."
 * Reuben Baron: "... to other writers."
 * Reuben Baron: "How did Steve return the Soul Stone to Red Skull?"
 * Christopher Markus: "There are times you might not like somebody but you have to give their stuff back. It could make a great one-act play!"
 * Markus implies that Steve would have to physically return the stone to Red Skull.
 * Steve has to physically arrive in the timeline and meet Red Skull.
 * Christopher Markus: "I think you would have... There's a fascinating one act play to be written of just Steve turning up and talking to the Red Skull."
 * While Markus here does not say that Steve necessarily did have to turn up and talk to Red Skull, he implies it.
 * Leaning toward that Steve has to physically arrive in the timeline and meet Red Skull.
 * Film School Rejects: ""Have you guys thought about whether or not Cap runs into Red Skull when he's returning the Soul Stone?" At this point the two writers seem to disagree as to whether Red Skull has been released from his bonds and therefore not there anymore. If there's no Soul Stone, there's no guardian right?"
 * Comic Book: "Co-director Anthony Russo brought it up first, asking the writers Christopher Markus and Stephen McFeely whether they had considered the idea. "He would have to," McFeely said, and Markus added that he had considered the question "many times". The pair speculated that just because the Soul Stone was gone, does not mean the Skull would have been freed from his obligation to guard its location. It might, Markus reasoned, come back. McFeely seems slightly less sure, wondering what he would be doing, just trapped there and waiting for something that might never happen, but before the argument could get too involved, Russo concluded, "It's fun to think about," and the commentary moved on."
 * The debate here seems to be more focused on whether Red Skull has been released from his bonds or not. The implication is that Steve having to physically return the stones is a given.
 * Leaning toward that Steve has to physically arrive in the timeline and meet Red Skull.

Result
Debatable: '''It would seem that Steve probably has to physically arrive in the timelines, somehow getting back to the rough time of the Time Heists and making it so that there is a complete set at all times. This also means that there is some precedent in the film for being able to navigate the timelines at least a little.'''

Can you navigate the system of timelines through the Quantum Realm?
Some sort of timeline-navigation is seemingly possible.
 * Unclear: Either Steve didn't have to physically return them in those timelines and just had to essentially recomplete the set just at the split points, or it is in some way possible to navigate the timelines.
 * It was later found that it's likely Steve does have to physically return them, so in some way navigating the timelines is possible.
 * Some sort of timeline-navigation is seemingly possible.

Anthony and Joe Russo
Seemingly not.
 * Joe Russo: "The question then becomes, how is he back in this reality to give the shield away?"
 * The brothers smile.
 * Joe Russo: "Interesting question, right? Maybe there's a story there. There's a lot of layers built into this movie and we spent three years thinking through it, so it's fun to talk about it and hopefully fill in holes for people so they understand what we're thinking."
 * The theory that he just used the space-time GPS to come out by the bench does not make sense, as all that device seems to do is shift you through time and space. It very much seems that there is no setting for which timeline you want it to jump to - that you shouldn't just be able to make jump laterally across timelines with it to another point in another timeline, you would have to be yanked back. Another problem with this is that, going by the Russo explanation, a jump with the GPS seems to create an alternate timeline, so Steve could not really get back to the main timeline with it as it would just cause a branch when he arrives - unless it is to be taken that all of the rest of the MCU is following that branch.
 * Seemingly not.

Result
Debatable: While some sort of timeline-navigation seems to be possible, for returning the Infinity Stones, it does not seem that making a fully lateral jump from one timeline to a similar point in time in another one is possible.

Is it possible to make a lateral jump between timelines (not just going back or forward in time or hitting return) with the space-time GPS?
Leaning toward yes.
 * Debatable: While some sort of timeline-navigation seems to be possible, for returning the Infinity Stones, it does not seem that making a fully lateral jump from one timeline to a similar point in time in another one is possible.
 * It would seem that he cannot just make a big jump using the GPS to go from his universe's 21st century to the main timeline's 2023 without coming out of the Quantum Tunnel. After all, it would be no different, by this interpretation, to the Time Heists - going back to a point in time, creating a new timeline, and then returning through the Quantum Tunnel mere seconds after they left when they hit the return button to come out. And even if it were possible to somehow do a tricky navigation of the timelines rather than just hitting return, why would he, when he can just hit return?
 * Leaning toward yes.

Films (factual)
Leaning toward yes.
 * Steve takes four vials of Pym Particles from Hank Pym's office.
 * If following the theory that this is for Steve to go and live with Peggy and then get back, then it would imply that - if Steve knows what he's doing - he would get back with a Pym Particle, i.e. through the Quantum Realm, rather than any other medium.
 * Leaning toward yes.

Anthony and Joe Russo

 * Joe Russo: "The question then becomes, how is he back in this reality to give the shield away?"
 * The brothers smile.
 * Joe Russo: "Interesting question, right? Maybe there's a story there. There's a lot of layers built into this movie and we spent three years thinking through it, so it's fun to talk about it and hopefully fill in holes for people so they understand what we're thinking."
 * One of the big problems with the Russos' explanation is that Steve seemingly should not be able to get back to the main timeline without coming through the Quantum Tunnel, as there is nothing in the film setting up a way he could come back without doing that. In the film, as is evidenced particularly by Hawkeye's test run, the Avengers are yanked back to their timeline's 2023. After the Hawkeye test run, they can hit a button to choose to do it themselves rather than just being pulled back after a certain amount of time. But still, they seem to essentially hit a "return" button and get yanked back like they are on a wire and harness, returning to a few seconds after they left, as programmed. So Steve should, if he's coming from an alternate timeline, just come back out of the Quantum Tunnel 5 seconds after he left, with no precedent for otherwise programming your suit to not yank back but still somehow get back to your timeline, just at a different time to when you left. And even if that were possible, why would Steve choose to do that, when he can just come out of the Quantum Tunnel as normal? After all, if he's in an alternate timeline, then he's coming back the exact same way that the Avengers did from Time Heist missions - travelling to a time, getting into an alternate timeline, then returning to the point a few seconds after you left. Why would he over-complicate things to come out at a different time or in a different way? And the Russos do seem to acknowledge that here, that there is a hole in their explanation. However, although it is unsatisfying, they are addressing the point and saying that an explanation exists, but it's intentionally mysterious. So this somewhat nullifies the hole, because it's somewhat as if they've explained it.
 * Leaning toward no.
 * Joe Russo: "He had to make another jump back to the main universe at the end to give the shield to Sam."
 * It's unclear if by this, Joe means a Quantum Realm time jump, or just some sort of across-timeline "jump", because the former should not be possible without coming out of the Quantum Tunnel. The latter would be what has to happen, but how he does so is a mystery - which is what the Russos had previously seemingly said it is supposed to be.
 * Unclear.
 * Reporter: "The question remains how Steve Rogers was able to return to the main timeline decades later, and with an intact vibranium shield to give to Sam Wilson. For Anthony Russo, the concept of the divergent timelines gave the film, and the cinematic universe, multiple layers that he particularly enjoyed."
 * This is pretty much a repeat of what they've been saying about how Steve's method of returning is a mystery.
 * Leaning toward no.
 * Anthony Russo: "There's a question of, how did this separate timeline Cap come to reappear in this timeline and why?"
 * Travis Clark: "And that's a story for another day?"
 * Joe Russo laughs.
 * Joe Russo: "Correct."
 * The Russos again seem to admit there is a gap in the logic of how that would work, but imply that that is intentional and has an explanation, therefore that it's not a mistake in their logic.
 * Leaning toward no.
 * Joe Russo: "But what's interesting about it - and you know people may... savvy people may come to ask how old Cap is in this timeline at the end of the movie."
 * Joe is suggesting that if you pay close attention you would ask why Cap is there, not that if you pay close attention you would work out why Cap is there, suggesting that the way Cap is there at the end is not provided in the film.
 * Chris Hewitt: "Yeah.... that is one of my questions."
 * Joe Russo: "That... that is an interesting story, isn't it?"
 * Chris laughs.
 * Anthony Russo: "Joe just brought up a question that we're not going to answer..."
 * Chris laughs.
 * Anthony Russo: "... interesting!"
 * Joe Russo: "That could be a..."
 * Chris Hewitt: "Okay."
 * Joe Russo: "... story for another time."
 * Anthony Russo: "Yeah."
 * Chris Hewitt: "Okay, interesting."
 * Joe Russo: "But, look..."
 * Chris Hewitt: "Should I ask it? Should I even just go - I'll go there and then you can do what - "How is old Cap in this timeline at the end of the movie?""
 * Joe Russo: "Well it's something that will be explained..."
 * Anthony Russo: "There's..."
 * Joe Russo: "... perhaps at some point."
 * Anthony Russo: "There's clearly, you know, in order for you to - in order for that to be, according to the rules of the movie that we set out, there's some missing story that, obviously that we're not getting in the film. We don't really want to delve into that missing story. I mean, the great thing about the MCU is, like, anything that doesn't show up on screen, anything that doesn't become text, is fodder for future storytelling."
 * This is the most explicit that the Russos have made it that their explanation has a hole in it but that there is an explanation intentionally left mysterious, so it's not actually a hole. This is in the context of what else they have said - in this quote alone, they don't actually specify that Cap went to an alternate timeline, they're just saying that how Steve is there at the end is not explained in the film, but later in the interview they say Cap is in an alternate timeline and have of course said that in other quotes.
 * Leaning toward no.
 * Joe Russo: "Now, what's also a story for another time is of course, if he created a branch reality, he would then have to use a Pym Particle to come back..."
 * Instead of saying it's a mystery how Steve would get back, Joe seems to just explain it here. It's odd, if this is supposed to be the reveal, it's very unceremonious and in a small interview and just the method from the film. Also, it seemingly shouldn't work - the reason this was a hole in the first place was because Steve couldn't just get back with the Pym Particle.
 * Anthony Russo: "Or..."
 * Joe Russo: "... to this reality..."
 * Anthony Russo: "... Yeah."
 * Anthony stops himself, but the way he interjects suggests he would say something like, "Or some other mysterious method," but that's only speculation. Still, the fact that he says "Or..." in response to using a Pym Particle to get back would perhaps imply that that was not intended as a reveal and the emphasis is just on the fact that Steve would have to get back to the main timeline, especially since Anthony stops himself once Joe gets to saying "to this reality", leaving the Pym Particle part behind. Joe also technically doesn't say he does use a Pym Particle, only that he would (seemingly) have to.
 * Leaning toward yes after all.
 * u/Reggie_48: "Can you help me/everyone understand how Captain America got back to the main timeline when he returned all the stones, because it contradicts the time travel theory stated by Banner earlier in the movie. Banner said that when you go back in time you make a separate timeline, so it doesn't [affect] the past, but if Captain America was in a different timeline when he returned the stones, how did he [get] back to the main timeline without the use of the quantum suits[?]"
 * The question is poorly phrased, anyway. I assume he means "Banner establishes that you make a new timeline" (incorrect) "so Captain America would have to have created a new timeline, which would mean he has to get back to the main timeline. But Steve isn't wearing the Quantum Realm suit, so he can't have gone to another timeline - except he has to have, so there's a contradiction here. Can you explain?"
 * The user is asking a fairly irrelevant question, as the Quantum Realm suits have been shown to just fold up instantaneously. A better question would be how Steve does not come out of the Quantum Tunnel there and then.
 * Russo brothers: "You are correct in that he would have had to have worn the quantum suit, using a Pym particle to make the jump."
 * The Russos again say that Steve would have made specifically a Pym particle jump. When they were mysterious about the method of Steve's return, it made more sense, because the problem was that he seemingly couldn't have used a Pym particle to return to the main timeline without coming out through the Quantum Tunnel there and then. But if he did, then that raises that problem again.
 * Russo brothers: "He's not wearing the suit on the bench, because that is not the exact moment to which he returned."
 * Despite the user not asking the more pertinent question of how Steve could have returned without coming through the Quantum Tunnel, the Russos have addressed it here, saying he did, just he came out at another time. It's not clear, however, how this would be possible, with the Avengers through the film simply hitting a return button and coming out at the programmed time a few seconds after they left, and no precedent for otherwise programming your return timeline, date, and time the way Steve would've had to here. It is also not clear how Steve could have sneaked out of the Quantum Tunnel at some previous time, implying that a) the new Quantum Tunnel has not only just been finished, for some reason they waited to return the stones, b) it was left unattended at some point, and c) that Steve knew a point when it was unattended to have programmed himself to come out of the Quantum Tunnel.
 * This puts paid to the argument that Steve must have come from an alternate timeline specifically because he "only just appeared on that bench, he didn't hide and then go and sit on it."
 * Seemingly yes, he just came out at a different time, something the film hadn't shown was possible.

Result
Debatable: Seemingly yes, he just came out at a different time, something the film hadn't shown was possible - potentially being the missing piece the Russos were referring to before.

If Steve were coming back from living in an alternate timeline, would he have to come out of the Quantum Tunnel?
The Russos claim there's a reason he's on the bench that fits with him having lived in a different timeline.
 * Debatable: Seemingly yes, he just came out at a different time, something the film hadn't shown was possible - potentially being the missing piece the Russos were referring to before.
 * According to the Russos, he came out of the Quantum Tunnel at a different time (for some reason), so there is potentially an option for the bench not being evidence he has been in the main timeline all along.
 * The Russos claim there's a reason he's on the bench that fits with him having lived in a different timeline.

Sean Carroll
It makes the most sense for this to be an indicator that he's been living in the main timeline, especially since there is no particular reason why Steve would come out of the Quantum Tunnel at another time.
 * Aylin Woodward: "But for Carroll, the biggest tell is how Steve appears on the bench at the end of Avengers: Endgame."
 * Sean Carroll: "Cap snuck in. He didn't materialize in the time machine, but knew when they'd be there and so just showed up at the bench at the right time."
 * This is indeed one of the two biggest pointers (along with the talk of Infinity Stones being what causes splits in the timeline), and it's good to know how a science adviser sees it based on the science/logic of the film.
 * It makes the most sense for this to be an indicator that he's been living in the main timeline, especially since there is no particular reason why Steve would come out of the Quantum Tunnel at another time.

Result
Debatable: '''It makes the most sense for this to be an indicator that he's been living in the main timeline, but it's not the only option. The Russos provide an explanation for their interpretation which means this is not a huge piece of evidence.'''

Christopher Markus
Possibly, but unclear. No explanation for provided for how this would fit with Steve, if this even is a thing.
 * Audience member: "What are the rules?"
 * Christopher Markus: ""What are the rules?" So glad you asked that. In the movie, the rules are basically: If you - you can go back, you can do whatever you want, it won't affect the future. Unless you take out an Infinity Stone, then it branches."
 * The wording "you can do whatever you want" is a little odd, as it suggests you are not bound by time, yet you're not creating a branch timeline. So you should just be stuck in the normal timeline. So does he in fact mean that "you can try to do whatever but you won't manage to change things"? Or might he in some way mean that you are free to do whatever you want, it won't stick as an actual part of the timeline unless a branch is created by removing Infinity Stones? That's a potential new concept. It doesn't seem to fit either Steve explanation, however, as it would leave him living in essentially a non-existent space.
 * Possibly, but unclear. No explanation for provided for how this would fit with Steve, if this even is a thing.
 * Christopher Markus: "There weren't fifty-five million paths because of every encounter that they had. So that - so that we could do things like have Captain America fight himself without that creating, you know, a cosmic problem as opposed to a physical problem between two people."
 * They wanted it to be so that you can't change time, and the branches are clean splits, so each individual encounter isn't a problem. This doesn't, however, clear up whether he is referring to the idea that the timeline's already split (so no worries about where it goes), or if this is in line with the new concept his previous comment might have implied: that whatever you do in going back will just not stick as a part of the timeline (only having an impact if it's in an alternate timeline because you removed an Infinity Stone). Again, not clear if he meant it that way.
 * Possibly, but unclear. No explanation for provided for how this would fit with Steve, if this even is a thing.

Clifford V. Johnson
Possibly stitching the universe differently and then just unstitching it, but unclear.
 * Clifford V. Johnson: Yeah, and you could argue instead of using multiverses, which perhaps is unsettling to some, it's our universe that's kind of being resewn in different - restitched in different ways, the narrative, you know, gets adjusted, but then you can go back at those insertion points and fix it."
 * An interesting way of putting it, from a science adviser to the film, which would align with Markus' comments about not wanting a multiverse to be involved.
 * Possibly stitching the universe differently and then just unstitching it, but unclear.

Result
Unclear: '''Possibly stitching the universe differently and then just unstitching it or just somewhat non-existent unless you remove an Infinity Stone, but unclear. No explanation for provided for how this would fit with Steve, if this even is a thing.'''

Can you do anything after Quantum Realm time-travelling back in time and it won't stick as an actual part of a timeline unless you remove an Infinity Stone?
Maybe some manner in which the timeline is stitched differently anyway before any Infinity Stone-removing actually splits the timeline, but likely not applicable.
 * Unclear: Possibly stitching the universe differently and then just unstitching it or just somewhat non-existent unless you remove an Infinity Stone, but unclear. No explanation for provided for how this would fit with Steve, if this even is a thing.
 * There has been a slight implication brought up that there might be something involved wherein they are able to meddle with events without any implications - alternate timelines, universes, or whatever - just restitching the universe until you remove an Infinity Stone, suggesting nothing is bound by time when Quantum Realm time-travelling to the past, so there is no problem with things being changed before an Infinity Stone is removed. However, this could just come down to a misinterpretation of an unclear quote, and does not fit with the writers' idea for Steve living through the main timeline, so it likely does not apply.
 * Maybe some manner in which the timeline is stitched differently anyway before any Infinity Stone-removing actually splits the timeline, but likely not applicable.

Films (in-universe, the characters might be mistaken)
Not made clear. It's possible that, due to the way the film is presented, there is a necessity for the idea that the Infinity Stones splitting the timeline splits it back to the point of arrival, and this could serve as an explanation. Nonetheless, the lack of explanation is a slight problem.
 * Bruce replaces the Time Stone, and the black line disappears.
 * Bruce Banner: "... it never left."
 * If it's only removing Infinity Stones in this film that makes the timeline split, how do you account for the fact that time is nonetheless changed by their actions before you remove an Infinity Stone? After all, the events in 2012 and 2014 are simply incompatible with the original timeline. It's not like until the stone is removed then they are stuck in a causal loop and time is the same as it always was, because certain things happen that cannot have happened, and what would've happened in the main timeline at the time the stones are removed, minutes later, in the new one? The 2023 versions of the characters who had been coexisting in the timeline just... disappeared? The first answer might be to say that it's not removing the stones from the time stream that makes the difference, but removing them from their intended place in space-time. But then you still have the problem of the Power Stone, which hasn't been moved yet when Rhodey knocks Quill out, and also still the question of what happened to the 2023 versions of the characters in the original timeline when the stones get moved, having been there for a few minutes. The other option is to essentially look at time somewhat in the scientific way where it's all laid out already and we're just moving through it. Since Infinity Stones get removed, it makes each one a branch timeline, and therefore was always going to be a branch timeline from the moment they arrived.
 * The removal of an Infinity Stone theoretically should indeed be somehow solidifying everything since arrival as a splinter timeline. The removal of an Infinity Stone definitely, explicitly splits the flow of time, so if the removal of an Infinity Stone were to only cause time to split at the point it were removed, you would end up with the Avengers being present in that time, and then a split when they go back leaving a timeline without an Infinity Stone, and a timeline still with it. Except, how? The Avengers going back is what removes the stone from the timeline, so you would have to have the split occur, say, the moment they hit the button to return, so in one version of events they disappear and in one they do not. So, why? Does it just not work? Why wouldn't it? And in that case, you also end up with versions of the Avengers abandoned in time (unless you end up with the timelines erased, but if timelines are indeed erased it is said to be the ones without Infinity Stones, so if there are also branch timelines with Infinity Stones, you wouldn't be erasing this) which is bizarre. You could question whether perhaps, because it's not actually said that it would be one timeline with stones and one without, maybe both timelines are missing a stone. That solves your stranded Avengers problem, except it is shown that removing an Infinity Stone creates one dark branch of reality specifically dark because it's missing an Infinity Stone, not that it poisons both timelines. Overall, this suggests that some sort of system where it would make everything since arrival an alternate timeline, thus meaning you were always in an alternate timeline since you arrived. Why the Infinity Stones would in some sense "choose" to do that is unclear, but if they didn't, it wouldn't fit with what the film presents, so this is just a possible necessary assumption. Tying in with Marvel's Agents of S.H.I.E.L.D., it would make sense that, in either case, if you are a time-traveller you somehow make the timeline after you arrive back in time volatile, less stable (after all, Marvel's Agents of S.H.I.E.L.D.: Season 6 shows that, for example, Deke Shaw is in a sense detectable as someone out of their natural time/universe, there is some sort of trace), and can take advantage of that or by removing an Infinity Stone cause that to be a split. The timeline, say, is like a piece of wood that has become weaker from the moment of arriving back, and if then a big nail is suddenly hammered in further down (Infinity Stone is removed), the wood will split, stretching back through the weaker wood to the point where it stopped being strong (back to arrival). This is not particularly making some sort of excuse for this version of removing an Infinity Stone somehow being different, since there does not seem to be any other way of removing an Infinity Stone anyway other than moving it to a different universe, so it would just be the rules of removing an Infinity Stone.
 * Not made clear. It's possible that, due to the way the film is presented, there is a necessity for the idea that the Infinity Stones splitting the timeline splits it back to the point of arrival, and this could serve as an explanation. Nonetheless, the lack of explanation is a slight problem.

Result
Unclear: '''Not made clear. Some possible suggestion that you are able to do anything before removing an Infinity Stone and it simply will not stick unless you remove an Infinity Stone, the argument but does not hold much weight and might not even have been the intention of the quotes behind it. It's possible that, due to the way the film is presented, there is a necessity for the idea that the Infinity Stones splitting the timeline splits it back to the point of arrival, and this could serve as an explanation. Nonetheless, the lack of explanation is less than ideal.'''

Novels
All parallel universes are alternate realities.
 * Felix Desta: "Do you think the Aether might be a Radical Quantum Selector?"
 * For context later.
 * Dissected later.
 * Felix Desta: "A lot of them would be similar to your own, while others could be totally different. Simply put, any reality you can think of? It exists. Sounds to me as if the Aether functions like a Radical Quantum Selector that allows its wielder to access these alternate realities and manifest them into our physical universe."
 * An interesting description of how the Aether works, and "alternate realities" = "parallel universes".
 * All parallel universes are alternate realities (not necessarily vice versa).

Films (in-universe, the characters might be mistaken)
Reality in its entirety is the tree of timelines, an individual reality is a branch of the timeline.
 * Ancient One: "Now this may benefit your reality, but my new one, not so much."
 * Realities = branches in the flow of time.
 * Realities = branches in the flow of time.
 * Ancient One: "In this new branch of reality, without our chief weapon against the forces of darkness, our world would be overrun. Millions will suffer."
 * The timeline branch is a branch of reality. So perhaps "reality" is the totality of branches - the tree of timelines - but also each branch of the timeline is a mini reality. Or it's just her way of saying branch reality.
 * Reality (possibly the totality of reality) = the tree of timelines.
 * Bruce Banner: "So..."
 * Bruce takes the Time Stone the Ancient One swiped aside.
 * Bruce Banner: "... chronologically, in that reality..."
 * Again using "reality" to mean timeline. I believe that reality as a whole is the tree of timelines, but each branch timeline is a reality.
 * Realities = timeline branches.

Joe Russo
Realities and timelines are the same, and are different worlds/universes.
 * Joe Russo: "He lived a completely different life in that world. We don't know how exactly his life turned out, but I'd like to believe he still helped many others when they were needed in that world. Yes, there were two Captain Americas in that reality..."
 * He adds a different "world" to the equivalent words with "timeline" and "reality". This implies that splitting the timeline does indeed contribute to the MCU ' s multiverse, that it's not in some sense the branch timelines of one universe but that the branches are universes themselves.
 * Worlds = realities.
 * Joe Russo: "For example, the old Cap at the end movie, he lived his married life in a different universe from the main one."
 * "Alternate reality" = "different universe".
 * Realities = universes.
 * Reporter: "Joe Russo pointed to two explanations of time travel in the MCU, one from Banner and the other from the Ancient One. Every action the heroes commit while in the past would result in the formation of a divergent timeline, or alternate reality, as a sort of butterfly effect."
 * Divergent timeline = alternate reality.
 * Timelines = realities.

Christopher Markus
Realities and timelines are the same.
 * Erik Davis: "So people are asking... Does this mean an old Captain America was hanging out this whole time while another Captain America was saving the day?"
 * Christopher Markus: "That is our theory. We are not experts on time travel, but the Ancient One specifically states that when you take an Infinity Stone out of a timeline it creates a new timeline. So Steve going back and just being there would not create a new timeline. So I reject the "Steve is in an alternate reality" theory."
 * Timeline = reality.
 * Timelines = realities.

Result
No debate: Realities, timelines, worlds, and universes are all interchangeable words.

Can you do anything after Quantum Realm time-travelling back in time and it won't stick as an actual part of a timeline unless you remove an Infinity Stone?
Maybe some manner in which time travel timelines do not contribute to the multiverse, but not clear and might not apply.
 * Unclear: Possibly stitching the universe differently and then just unstitching it or just somewhat non-existent unless you remove an Infinity Stone, but unclear. No explanation for provided for how this would fit with Steve, if this even is a thing.
 * There has been an implication brought up that there might be something involved wherein the writers did not want a multiverse to be created by Avengers: Endgame, and it is unclear if this is because things were erased or because the single universe was in some way meddled with without any implications - alternate timelines, universes, or whatever - just restitching the universe until you remove an Infinity Stone. However, this could just come down to a misinterpretation of an unclear quote, and does not fit with the writers' idea for Steve living through the main timeline, so it likely does not apply.
 * Maybe some manner in which time travel timelines do not contribute to the multiverse, but not clear and might not apply.

What are the definitions?
Timelines are universes, parts of the multiverse.
 * No debate: Realities, timelines, worlds, and universes are all interchangeable words.
 * Timelines should be equivalent to new universes, so part of the multiverse.
 * Timelines are universes, parts of the multiverse.

Films (in-universe, the characters might be mistaken)
The different dimensions are parts of the multiverse.
 * Ancient One: "We harness energy drawn from other dimensions of the multiverse."
 * The different dimensions are parts of the multiverse.
 * The different dimensions are parts of the multiverse.

Novels
There exists parallel universes in the multiverse, implying ones not branching in a related tree.
 * Darcy Lewis: "But the Aether isn't a stone... it's like a... blood cloud?"
 * Jane Foster: "Correct. And there's a reason for that. The Aether is the Reality Stone. While it was inside me, I experienced only a fraction of its abilities. Its shapeless form can possess a host body and give the body unlimited strength and unpredictable power. We knew that. But in its solid form, it can create illusions and twist our perceptions."
 * Felix Desta: "Then it is a Radical Quantum Selector! Hugh Everett III, the super-famous physicist, proposed that there are an infinite number of parallel universes out there.
 * This is presented as if Desta has hit on the truth, implying that indeed, there are an infinite number of parallel universes. Parallel would imply never meeting - that there are entirely separate universes (not referring to ones that branch from each other).
 * There exists parallel universes in the multiverse, implying ones not branching in a related tree.

Anthony and Joe Russo
Timelines are universes, parts of the multiverse.
 * Sonaiya Kelley: "Was it difficult presenting a theory of time travel that hadn't previously been explored onscreen?"
 * Anthony Russo: "Back to the Future is one of our favorite films, and the rules of that movie are ubiquitous; they have informed pop culture for 40 years. And we wanted to do something different. We didn't realize how complicated it would be to create new rules and have people go with us, but we learned very early on in the test screenings that people are really committed to those Back to the Future rules - if you shoot yourself, you should die. We spoke with a few physicists, and there's a lot of theories about how time travel could work. We chose the multiverse theory."
 * So, timelines are indeed related to the multiverse.
 * Timelines are universes, parts of the multiverse.
 * Joe Russo: "And anything you do in that time shift would create a multiverse reality. It will create a new future, but it's not going to affect your past."
 * Again, the multiverse appears to be related at least in part to alternate timelines.
 * Timelines are universes, parts of the multiverse.
 * Joe Russo: "What's most compelling is that this is a multiverse."
 * Again, the multiverse is indeed related to timelines.
 * Timelines are universes, parts of the multiverse.
 * Jessica Shaw: What... he's in an alternate reality so this is not like a Ray Bradbury situation?
 * Joe Russo: "Well so, so what happens is we're playing with a different form of time travel, it's the multiverse notion of time travel."
 * Again, the time travel is indeed related to the multiverse.
 * Timelines are universes, parts of the multiverse.
 * Joe Russo: "Our interpretation of that is a multiverse, which we just think is a lot of story potential."
 * Joe talking about the multiverse here possibly touches on a wider debate rather than just Captain America's ending, as the "multiverse" is not really the direct answer to the Cap question. So, either Joe simply means, "Our interpretation is that the answer to Cap's situation relates to the multiverse, being another universe," or he's referring to a larger point, "Our interpretation of the time travel rules is that it creates a multiverse." It appears to be the latter, as it follows on from Joe talking about the rules in the film, rather than the general point he's making about there being a disagreement over Captain America. This also implies that there is an interpretation where it is not the multiverse that's involved, lining up with the implication from the writers talking about how they didn't want a multiverse.
 * Timelines are universes, parts of the multiverse.

Christopher Markus and Stephen McFeely
Maybe some manner in which time travel timelines do not contribute to the multiverse, but not clear and might not apply.
 * Jeff Goldsmith: "Did you ever decide that there was maybe a moment you were gonna get into the multiverse?"
 * Stephen McFeely: "It clearly exists, right? Because Doctor Strange has talked all about it. I mean that's, it's part of the fabric of that. We may not - this may be where I disagree with Marvel or where they're going, I have no idea where Kevin Feige is going, I don't know what's happening tomorrow, I have no idea."
 * Christopher Markus: "Are you okay?"
 * Stephen McFeely: "But I'm a big believer in stakes, and if you tell me that I can just go and get another Natasha and another Tony and we can keep rolling, then particularly my grandma is gonna go, "Well why did I watch that?" So yeah we are retraining the audience all the time. There may be - I may be wrong 2 years from now where people want, "I want all sorts of stories from people I already lost.""
 * Christopher Markus: "Well particularly in a movie where we are very much heading towards some final resolutions, toward things ending, toward people leaving. If you go, "Yeah but there's seventy-five Tonys out there, like seventy-five billion Tonys out there," your drama is gonna suffer."
 * Markus and McFeely seemingly are discussing how they did not want the film to be establishing a multiverse. This could mean that timelines do not count towards the multiverse, only entirely separate universes, for whatever reason. it could refer to the idea of erasing the timelines.
 * Different timelines might not contribute to the multiverse.
 * Christopher Markus: "So we could tighten up the possibilities. Because writing is all about just winnowing down the possibilities, the worst moment in any project is when you have too many options. And so, ideally, as time goes on, you're killing off options to get to one story. Which is why, people get exci- when people get excited about the multiverse, I just stare at them like, "Wha-? You can'- your stakes are gone!", like if, "Well, 1 inch over, there's a room where this didn't happen," it's like, "Well then why are we telling this story?" You know, "Oh, your dog died? Let's go over there and get your other dog from...", you know. So while it, you know, may be a fascinating idea, it's pretty hard on drama. But the time travel, on the whole, was actually great for drama, it turned out."
 * Markus again implies that they did not want to be creating a multiverse with this, though it is unclear in what way they intended to avoid this - it's possible they're referring to timelines not being equivalent to universes.
 * Different timelines might not contribute to the multiverse.

Result
Debatable: '''While there is some evidence that suggests that maybe timelines are not universes contributing to the multiverse, it is unclear and might just refer to the erasing of timelines. There is more, clearer evidence that timelines are equivalent to universes. So, branch timelines each are universes of their own. As well as this, there is evidence that different dimensions are parts of the multiverse and that there are parallel universes, i.e. never crossing in their history with the main universe. So, branch universes and parallel universes both comprise the multiverse.'''

Films (factual)
The other futures might have just been hypothetical, but maybe not. At least in some way preventing the other futures from ever happening/lessening their validity.
 * Doctor Strange: "To see all the possible outcomes of the coming conflict."
 * "Possible outcomes" would suggest that these are in some way only hypothetical, not actually physically realised in some way. However, coupled with the previous sentence, "I went forward in time to view alternate futures," it would appear more that Strange is saying that he wanted to see the possible outcomes, so he went forward in time to view alternate futures. So the futures themselves are not necessarily hypothetical/not realised physically.
 * The other futures might have just been hypothetical, but maybe not.
 * Star-Lord: "How many did you see?"
 * Doctor Strange: "Fourteen million, six hundred and five."
 * Tony Stark: "How many did we win?"
 * Doctor Strange: "One."
 * The nature of all these different "alternate futures"/"possible outcomes" raises questions about how exactly the Avengers' success in Avengers: Endgame works. Does it mean that all fourteen million, six hundred and five different futures played out in individual branching timelines and that the films have simply just decided to show the one where things played out well? That would mean that their efforts weren't particularly important, the films essentially just decided to follow the timeline where their efforts paid off and not the millions of other ones were they failed, rather than the Avengers specifically managing, with Strange's help, to make the necessary sacrifices and guide the single universe/timeline to a successful result. The fact that it is presented the latter way would suggest that the other fourteen million, six hundred and four futures in some way did not come to pass, that they are not equally valid timelines out there in the multiverse. The Russos' later comments about this help a little.
 * In some way preventing the other futures from ever happening/lessening their validity.

Anthony and Joe Russo
They were never alternate timelines. They just made their one timeline positive.
 * @simplymarrisa: "Serious question: when [Doctor] Strange is seeing all the scenarios for how the war could end, does he see it like a montage or a movie? How do you as the creators see this happening in his brain[?]"
 * Anthony Russo: "This is a great question..."
 * Joe Russo: "Yeah..."
 * Anthony Russo: "... and it's..."
 * Joe Russo: "... it's cool."
 * Anthony Russo: "... I mean, Strange has to exert an immense amount of energy into goi- - to go into this state, and the amount of time that he's in this state, as we know from, from the history in his own standalone film, Doctor Strange, he could be in that, in that state for... who knows how long? So it could have taken Strange an immensely long time to actually review all these scenarios."
 * Joe Russo: "He has to physically live them..."
 * Anthony Russo: "Yeah."
 * Joe Russo: "... and then die in each of them, and right before he dies he has to reset it, as we saw at the end of Doctor Strange, and do it again - and take copious notes each time he does it."
 * While, in my opinion, this was not clear in Avengers: Infinity War, the Russos are explaining that what Strange is doing is essentially the same as his loop with Dormammu, trapping them in a time loop (not the big time travel type) where events then play out as normal, but are reset each time, returning to that moment on Titan, until he's done and breaks out of it, having to everyone else's point of view, not gone anywhere. He hasn't meddled with the timeline in any way, just gone around a tangential loop fourteen million, six hundred and five times that always resets to that point on Titan. This solves the problem of whether there are fourteen million, six hundred and four timelines out there where things turned out badly, of whether the films were just happening to follow the one timeline where things turned out well and the Avengers didn't actually particularly achieve saving things, of whether Strange would have been seeing millions of timelines in which he had already seen the millions of timelines. There's no multiple timeline stuff going on with Strange, it's just one of his Dormammu loops, and then the Avengers manage to make things happen similarly to the one outcome he saw in his loop where things turned out well.
 * They were never alternate timelines. They just made their one timeline positive.

Result
No debate: '''While the film isn't clear, the Russos have clarified that Strange is doing the same thing he did with Dormammu, so they're not branch timelines, just a loop around a point in time like with Dormammu. The Avengers just made their one timeline have a positive outcome.'''

In what fashion do the Avengers succeed in Avengers: Endgame?
Not applicable.
 * No debate: While the film isn't clear, the Russos have clarified that Strange is doing the same thing he did with Dormammu, so they're not branch timelines, just a loop around a point in time like with Dormammu. The Avengers just made their one timeline have a positive outcome.
 * So, this has nothing to do with universes splitting.
 * Not applicable.

What are the definitions?
The universes do "split" in some fashion into two, the two are not just parallel universes.
 * No debate: Realities, timelines, worlds, and universes are all interchangeable words.
 * When a timeline "splits", it should mean that the universe also "splits".
 * The universes do "split" in some fashion into two, the two are not just parallel universes.

Films (in-universe, the characters might be mistaken)
Branches/splits in time occur, presumably meaning the same thing as branches/splits of universes occurring.
 * Karl Mordo: "Temporal manipulations can create branches in time."
 * Branches in time, whatever that exactly means, can be created when manipulating time.
 * Branches in time are possible, which would suggest branched timelines, and therefore branching universes rather than just parallel ones.
 * Doctor Strange: "I went forward in time to view alternate futures."
 * It's unclear exactly what Strange means by "alternate futures". The fact that he specifically says "I went forward in time", though, would suggest that it was a physical exploration of these futures, not just a look at different possibilities as the rest of the quote might otherwise suggest. The phrasing would imply some sort of branches after this point in the timeline, but the exact structure and rules are left unclear.
 * Leans toward branches in time - so presumably branching universes - depending on what this scene means.
 * Bruce Banner: "With all due respect, alright, I - I'm not sure the science really supports that."
 * The Ancient One conjures a magic timeline, with the six Infinity Stones circling it.
 * Ancient One: "The Infinity Stones create what you experience as the flow of time. Remove one of the stones..."
 * The Ancient One swipes the Time Stone from the line, and a black line splits from the magic timeline.
 * Ancient One: "... and that flow splits."
 * Specifically said that the flow of time "splits", in two as shown.
 * The flow of time splits, which, if there were any doubt, has been confirmed by writers to mean splitting timelines. If timelines are equivalent to universes, this would mean specifically that the universes split in two.

Marvel's Agents of S.H.I.E.L.D. (in-universe, the characters might be mistaken)
Universes can spin out of existing ones in some way, but this is perhaps different to the splitting of the universes through time travel-related means.
 * Leo Fitz: "Hmm, I'm not sure you actually know what "multiverse" means."
 * Deke Shaw: "That every choice we make spins out a different timeline into the cosmos, and right now, there are infinite parallel universes."
 * If Deke is correct, different timelines spin out from each timeline, and that's what creates parallel universes. The show later suggests that Deke's multiverse theory was correct, implying this too was correct.
 * With problems with the idea of infinite branches such as Robin's powers, the White Monolith just sending them to one future (if it didn't, you'd get many agents returning to the same 2017), it's possible that the idea of spinning out universes is somewhat separate from the "chang[ing]" of time in The End, being more of an explanation or the existence of the multiverse.
 * Universes can spin out of existing ones in some way, but this is perhaps different to the splitting of the universes through time travel-related means.

Joe Russo
Universes are created by the events of Avengers: Endgame, they don't just exist themselves and are travelled into.
 * Joe Russo: "... it's just like what Hulk said, what happened in the past has already happened. If you go back to past, you simply created a new reality."
 * New realities are created, not existing on their own.
 * Universes are created by the events of Avengers: Endgame, they don't just exist themselves and are travelled into.
 * Joe Russo: "For example, the old Cap at the end movie, he lived his married life in a different universe from the main one."
 * Previously stated that he "created an alternate reality", and now stated that "alternate reality" = "different universe", so the timeline stuff in Avengers: Endgame would have "created" different universes.
 * There is a question of in what fashion universes split. Is it a single universe up to a point in time and then it splits like a monozygotic twin or mitosis? Is it essentially a copy-and-paste of the universe at that point, two universes with an identical history but not literally a shared single history? Is it two parallel universes that that just happen to be identical up until the point when people arrive through time? The latter seems unlikely, as it would require the time travel to somehow select a universe that it is pretty much identical up until the point in time of the destination.
 * Universes are created by the events of Avengers: Endgame, they don't just exist themselves and are travelled into.

Christopher Markus
Timelines, so presumably also universes if the definitions equate, are created by the events of Avengers: Endgame, they don't just exist themselves and are travelled into.
 * Erik Davis: "So people are asking... Does this mean an old Captain America was hanging out this whole time while another Captain America was saving the day?"
 * Christopher Markus: "That is our theory. We are not experts on time travel, but the Ancient One specifically states that when you take an Infinity Stone out of a timeline it creates a new timeline. So Steve going back and just being there would not create a new timeline. So I reject the "Steve is in an alternate reality" theory."
 * The removing of a stone "creates" a timeline, it's not a separately existing timeline.
 * Timelines, so presumably also universes if the definitions equate, are created by the events of Avengers: Endgame, they don't just exist themselves and are travelled into.

Result
No debate: '''The universes do "split" (when the timeline "splits" - they are established as interchangeable) in some fashion into two, as a branch. The splitting is a creation of a new universe, it exists because of the events of Avengers: Endgame. While from the perspective of the timeline, it just splits when it splits, it only splits because of the events of Avengers: Endgame (or whatever else, like The End). You don't have just two parallel universes in these cases, universes that you just travel into that happen to be otherwise identical. Universes can spin out of existing ones in some way, but this is perhaps different to the splitting of the universes through time travel-related means.'''

In what fashion do universes "split"?
When you travel back in time then you are in the same stem universe, so were also in the past of the main timeline because it's the single stem universe's past.
 * No debate: The universes do "split" (when the timeline "splits" - they are established as interchangeable) in some fashion into two, as a branch. The splitting is a creation of a new universe, it exists because of the events of Avengers: Endgame. While from the perspective of the timeline, it just splits when it splits, it only splits because of the events of Avengers: Endgame (or whatever else, like The End). You don't have just two parallel universes in these cases, universes that you just travel into that happen to be otherwise identical. Universes can spin out of existing ones in some way, but this is perhaps different to the splitting of the universes through time travel-related means.
 * The universes split apart, which would suggest when you travel back in time then you are in the same stem universe, so were also in the past of the main timeline because it's the single stem universe's past.
 * When you travel back in time then you are in the same stem universe, so were also in the past of the main timeline because it's the single stem universe's past.

Joe Russo
Joe Russo doesn't mention this, but the universes specifically should split in the monozygotic/mitosis manner, so when you travel back in time then you are in the same stem universe, so were also in the past of the main timeline because it's the single stem universe's past.
 * Joe Russo: "For example, the old Cap at the end movie, he lived his married life in a different universe from the main one."
 * The fashion in which universes split is important for then considering the question of what happens if characters from one of the subsequent universes then goes back in time. If they go back in a causal loop, does that mean that they feature in the history of both universes? If the universes split like monozygotic twins/mitosis, then going back in time means going back to the single stem, so appears in the shared history of both. If they were then still around at the point that the universe splits, then you end up with a version of the character in each timeline as with anyone else present at the time of the split.
 * If the universe essentially copy-and-pastes, including its history, up to the point of copying, it is more complicated. The copy-and-pasted universe would then have a character going back into its history. However, the whole idea of a causal loop is that, while the perspective changes for the character moving in time, time itself is not changing and is just playing out with that character having arrived in the past. In which case, for the copy-and-pasted history to include the character having come back from the future, the original history must include that character having come back from the future, despite it being the other universe's future. Which then means that that character from the other future is around at the time of the anchor, so still around in this universe's future as well after the anchor point. So essentially, the copy-and-paste idea would function almost identically to the idea of a monozygotic/mitosis split, albeit just with the idea of them still being distinct universes and always having been, just identical up to a point for this reason instead of literally the same universe. After all, the "copy-and-paste" phrasing I have used may be slightly misleading, as it implies the universe only comes into existence at a certain point. While that universe would only exist through being "created" from the main universe, it would still have its own full history of time so would have always existed, only this would be its reason for existing. So there would be no before and after with the copy-and-paste, it would more be like the two universes' histories are in sync. Essentially, this explanation doesn't particularly make sense, because it would require the main universe to have a character from another universe in it without that character ever crossing between universes or being in some stem timeline.
 * The third option, just two universes happening to be identical up to the point of the change, has the same problem. It is essentially the same as the second option when it comes to this problem, the only difference being the reason for these universes existing - in this case, the universes are just entirely separate, but have to be identical. To have an identical history, you would require the character to be present in both histories without any reason to be existing in the main universe's past. So, if causal loop time travel is possible (which seems true from at least some of this), this means that, most likely, the fashion in which universes split should be the monozygotic/mitosis manner.
 * Joe Russo doesn't mention this, but the universes specifically should split in the monozygotic/mitosis manner, so when you travel back in time then you are in the same stem universe, so were also in the past of the main timeline because it's the single stem universe's past.

Result
Debatable: '''The universes specifically should split in the monozygotic/mitosis manner, so when you travel back in time then you are in the same stem universe, so were also in the past of the main timeline because it's the single stem universe's past. If you were then around still at the time of the split, you end up with a version in both universes, so you have ended up with a version of the character from one branch universe in the other universe post-split.'''

Sean Carroll
Leans toward he's her husband, but there are other explanations in-universe.
 * Sean Carroll: "When Cap went back to the 1970s [to retrieve the Tesseract and Pym Particles with Tony Stark], there's a picture of Steve Rogers on her desk. If she married someone else, that'd be weird."
 * Carroll makes a good point here. Sure, maybe Peggy was simply divorced by 1970 and went back to having him on her desk. Maybe she just has his picture on there for the memory of her friend. But Peggy decided to move on from keeping Steve's photo in 1946, so it would be odd for it to be either of those two reasons. If she had Steve back, that would make sense, while being a way to keep a photo of him without arousing suspicion. So whatever the case, her having his picture on her desk would not particularly make sense if she married someone else in the main timeline.
 * Leans toward he's her husband, but there are other explanations in-universe.

Result
Debatable: Leans toward he's her husband, but there are other explanations in-universe.

Christopher Markus and Stephen McFeely

 * Jeff Goldsmith: "Wait, is that a thing? If people rewind Civil War, would they see an old version of him at the funeral?"
 * Stephen McFeely: "No, no, no, no, no."
 * Christopher Markus: "But feel free to legally download Civil War and investigate."
 * They confirm that the theory of the old man pallbearer being older Steve is incorrect, but nonetheless that older Steve would be present - just not shown on-camera.
 * No, but he is supposed to be at the funeral according to the writers.

Result
No debate: No, but he is supposed to be at the funeral according to the writers.

Joe Russo
He chose to rest, it wasn't about wanting to change anything.
 * Xiang Rong: "Did Captain America's action at the end affect the timeline? Does that mean there was a time where two Captain Americas existed in a same universe?"
 * Joe Russo: "To me, Captain America's action in the end wasn't the fact he wanted to change anything, it's more like me has made a choice. He chose to go back to past and lived with the one he loved for the rest of his life."
 * I will address the thing about Captain America not interfering with the past later, but this also contributes to that, Joe Russo saying he didn't want to change anything.
 * He chose to rest, it wasn't about wanting to change anything.

Christopher Markus
He chose to rest, it wasn't about wanting to change anything.
 * Reuben Baron: "As for why Steve wouldn't, for example, stop the Kennedy assassination if he were in the main MCU...
 * This is not how a time loop works. If it were a time loop, as the writers suggest, then Steve would be unable to change anything, such as stopping the JFK assassination.
 * Reuben Baron: ... Markus passed the buck."
 * Christopher Markus: "We don't have to write that!"
 * As Markus goes on to discuss in a later interview, even without the science of the time loop preventing Steve from interfering, they still felt Steve would not interfere anyway. Markus alludes to that here.
 * He chose to rest, it wasn't about wanting to change anything.
 * Christopher Markus: "Because I mean, you get Captain America loyalists who say that if Cap goes back in time he is honor-bound to fix everything he knows is going to happen, so he has to go and save Bucky, he has to prevent the Kennedy assassination, he's a very busy man."
 * Markus here addresses a criticism some fans have raised with the idea of Steve being in the same timeline. It is a false criticism, however, as a time loop does not allow for changing time - by the writers' interpretation that only removing an Infinity Stone causes a split in the timeline, Steve would have no option of changing events. He would just be a part of the MCU timeline that always was this way and so always is this way. Markus does not address that part of the response to this criticism here, though, but that comes up later.
 * Christopher Markus: "But that's not why we sent him back. We sent him back so that he can become a whole person and finally come home from a war. So, we didn't want him to go back and just keep adventuring, we wanted him to rest, and the only way we could come to that solution is if there are two Caps, which I'm okay with.
 * So, as well as the discussion later of how it simply is not necessarily valid anyway, the writers also have intended that Steve would not be trying to save everyone and change everything anyway.
 * He chose to rest, it wasn't about wanting to change anything.

Clifford V. Johnson
In a time loop, it is not possible for Steve to change anything, no matter how hard he tries. It's just not even an option.
 * Clifford laughs.
 * Christopher Markus: "... and whether that breaks all our own rules."
 * Clifford V. Johnson: "Right!"
 * Clifford laughs.
 * Clifford V. Johnson: "I have a way out for you on that..."
 * Christopher Markus: "Thank you."
 * Clifford V. Johnson: "... but we can get to that."
 * They joke again about the Captain America debate.
 * Dissected later.
 * Clifford V. Johnson: "If time travel to the past is possible, it might be in some limited way that somehow makes sure that all narratives make sense. And that's what I think's gonna be the way out, for..."
 * Clifford is referring back to what he said earlier, that he had an explanation for Captain America to make it work. So this is that explanation.
 * Kim Griest: "That's super cool, that's kind of like Hawking's "chronology protection"..."
 * Clifford V. Johnson: "Yeah."
 * Kim Griest: "... conjecture..."
 * Clifford V. Johnson: "So..."
 * Kim Griest: "... but..."
 * Clifford V. Johnson: "... it'll be..."
 * Kim Griest: "... it's a..."
 * Clifford V. Johnson: "... like..."
 * Kim Griest: "... little..."
 * Clifford V. Johnson: "... "narra-"..."
 * Kim Griest: "... weaker."
 * Clifford V. Johnson: "It'll be the "narrative protection conjecture"."
 * Kim Griest: "Interesting!"
 * Clifford V. Johnson: "You heard it here first, folks. Right? And so, it might be that from some person's point-of-view I made a time machine and I did a thing, from everyone else's point-of-view, you won't even notice that time travel has happened because you're just moving toward your future, even though from some perspectives, it's kind of went around and went to someone else's past."
 * Here, Clifford, a science adviser to the film, discusses a version of time travel, to do with time loops, where you do not actually affect time per se, you're just in the timeline. The time-traveller's perspective is the only thing that has shifted.
 * Clifford V. Johnson: "And I think there may be logical ways that the unive- - you know, it might be, you, you know - going back to H. G. Wells, right? You make the time machine, you go back in time, and then every time you try and do something that would stop you from making that time machine that would've sent you back, something happens: you trip over a wire, you, you know, an earthquake happens, and the universe somehow just, the physics propagates in such a way as to protect the narrative in some sensible way."
 * 'Clifford is therefore saying that he feels the way out for the Steve situation is that he simply went back in the timeline and lived through it again, and had no choice to change anything. This is how time loops would work, you are simply in the timeline, things would happen the way they always did because they are the things that always did happen, it's the same events. Not identical events, literally the same ones. And if you like, it can be seen as the universe/timeline protecting itself, protecting its narrative, as Clifford puts it here. Steve could try to change things, but every time he does, he will just trip over a wire, be caught in an earthquake, etc., no matter how unlikely. And if, at any point in the MCU films, people had looked up earthquakes that happened in the past, there always would have been one on the date Steve then experiences one on in the past. Because it's the same timeline. No matter how unlikely, if Steve were to keep trying he would always be caught in those earthquakes or whatever other incidents that prevent him, because he can't succeed, because he didn't succeed, because time played out this way. This explains why the argument that Steve should have stopped certain events from happening is not applicable - it's not how the science of the time loop would likely work, as Clifford V. Johnson here explains. This is similar to Simmons' invincibility tests in Marvel's Agents of S.H.I.E.L.D.: Season 5. She goes through stunts where she should almost certainly die, yet is confident that she won't, because she can't, because she knows she survives into at least the 2020s. And she doesn't die despite the odds, because, from a certain perspective, the timeline is protecting her. She doesn't die in 2018-2022 because she doesn't die until post-2022, she doesn't die until post-2022 because she doesn't die in 2018-2022, she doesn't die in 2018-2022 because she doesn't die until post-2022, etc.. Steve doesn't successfully (if he even tried) save Bucky from Hydra in 1948-2014 because Bucky doesn't escape Hydra until 2014, Bucky doesn't escape Hydra until 2014 because Steve doesn't successfully save him from Hydra in 1948-2014, Steve doesn't successfully save Bucky from Hydra in 1948-2014 because he doesn't escape Hydra until 2014, etc.. And, because of this, it would be useless for Steve to try. He might as well rest, and in combination with the writers' comments, I believe from all of this that it can be concluded that he rested, knowing there is nothing that can be done, but that the world will be overall okay by 2023 anyway, and now he can just rest with Peggy. It's essentially like Steve has just been transported into a cinema, with Peggy, to watch the MCU films play out and spend time together while they do it.'
 * Imagine it like this: Someone who has seen the near future sits you down and puts a pencil in front of you, and they tell you they know with 100% certainty, having seen it, that you will not pick up the pencil. You could think, "Oh, really? Well what if I just... do." And you go to pick it up, but then think, "But apparently I don't. I wonder why that is?", and pause. But, "No, why not? I'll just do it, I'm curious. Why shouldn't I?" And then you try, and pause again, "But what if they're playing mind games with me? I mean, why would I pick up the pencil otherwise, if I hadn't specifically been told I don't? Why should I? No, I just won't." And then you decide not to. But then you think, "But now I'm just playing directly into this supposed future of not picking it up, it's all happening because of this thought. I'm overthinking it, I'll just pick up the pencil. But I'm still reconsidering. And I guess I don't pick it up because I'm reconsidering, so the fact that I'm thinking this is the reason I don't pick it up, which is the reason I then get told about it and end up thinking like this." Whatever happens, you're not going to manage to pick up the pencil. You might even just go for it, but then there will be an earthquake or something similar, you never pick up that pencil. The earthquake didn't happen to prevent you picking up the pencil. It just happened, and prevented you from picking up the pencil. And the person who spoke to you then saw that, so could tell you that they knew you wouldn't manage to pick it up. This is the situation Steve would find himself in. He essentially has been told that he will not successfully rescue Bucky or stop assassinations, or whatever else, because he has lived through that history. So whatever he tries, it cannot affect anything, because time is just playing out. Events will play out the same because they are literally the same events just being experienced again.
 * In a time loop, it is not possible for Steve to change anything, no matter how hard he tries. It's just not even an option.

Result
No debate: '''In a time loop, it is not possible for Steve to change anything, no matter how hard he tries. It's just not even an option. And even if it was - and it's not - he chose to rest, it wasn't about wanting to change anything. This argument not a problem for the idea of a time loop.'''

Are Infinity Stones the only things splitting the timeline in Avengers: Endgame?
It would seem that Infinity Stones are the only things splitting the timeline, so no.
 * Debatable: Leaning toward yes, but possibly no.
 * If Infinity Stones are the only things splitting the timeline, then Steve and Clint, making jumps not involving Infinity Stone-removal, would not open alternate timelines.
 * It would seem that Infinity Stones are the only things splitting the timeline, so no.

Does merely arriving, after travelling back in time via the Quantum Realm, split the timeline?
It would seem that merely arriving doesn't split the timeline, so no.
 * Debatable: The films and Markus and McFeely suggest no, while the Russos suggest yes. Scientist Eric Michelsen's comment would seemingly slightly support the Russos, but the films and writers together have more weight, especially with the massive problem of returning the stones if the timeline splits - so it would seem that no, merely arriving does not split the timeline. But there is definitely uncertainty.
 * If merely arriving, after travelling back in time via the Quantum Realm, doesn't split the timeline, then since Steve and Clint then don't remove Infinity Stones, the answer would be no.
 * It would seem that merely arriving doesn't split the timeline, so no.

Is Peggy's husband not previously being revealed significant concerning whether Steve stayed in the main timeline?
Would mean no, they didn't open a new timeline.
 * No debate: Yes, the writers wanted to exploit that missing information to make Steve the husband, and might even have semi-planned it all along, with that goal in mind - regardless of whether that ends up working with the time travel rules.
 * The writers intended to build into the existing MCU that Steve would be Peggy's husband all along, so always in the main timeline, hence not opening a new timeline.
 * Would mean no, they didn't open a new timeline.

If Steve were in the main timeline all along, how could Steve have stayed there throughout without being found out?
This does not pose much of a problem for the idea that they did not open a new timeline.
 * No debate: If indeed he were in the main timeline all along, he lived a simple, stay-at-home life, hidden away, and changed his identity.
 * It has been said he would stay hidden away, so it's not a problem.
 * This does not pose much of a problem for the idea that they did not open a new timeline.

Is the fact that Steve is just found sitting on the bench evidence toward whether he did or did not live in a different timeline?
Leaning toward no, but not necessarily.
 * Debatable: It makes the most sense for this to be an indicator that he's been living in the main timeline, but it's not the only option. The Russos provide an explanation for their interpretation which means this is not a huge piece of evidence.
 * It leans toward that he's been living in the main timeline, but it's possible, according to the Russos, that he wasn't.
 * Leaning toward no, but not necessarily.

If merely arriving in the past via Quantum Realm doesn't split the timeline itself, how do you account for the fact that time starts changing before stones are removed?
Not particularly applicable.
 * Unclear: Not made clear. Some possible suggestion that you are able to do anything before removing an Infinity Stone and it simply will not stick unless you remove an Infinity Stone, the argument but does not hold much weight and might not even have been the intention of the quotes behind it. It's possible that, due to the way the film is presented, there is a necessity for the idea that the Infinity Stones splitting the timeline splits it back to the point of arrival, and this could serve as an explanation. Nonetheless, the lack of explanation is less than ideal.
 * Would lean toward that they did open alternate timelines, but it's possible that they didn't, and as well as this, it would in some ways seem necessary that there be some assumption because there are issues with the idea that arriving in the past via Quantum Realm does just split the timeline itself. Not just the ones previously listed, but specifically pertaining to this, it does not solve the problem, so this is somewhat of a wash.
 * Not particularly applicable.

Does Peggy having Steve's photo on her desk provide evidence concerning which timeline Steve lived his life in?
Leaning toward no, but not necessarily.
 * Debatable: Leans toward he's her husband, but there are other explanations in-universe.
 * Makes more sense if Steve is Peggy's husband, so Steve wouldn't have made a new timeline, but there are possible explanations.
 * Leaning toward no, but not necessarily.

Is the old man at the funeral in Captain America: Civil War evidence concerning which timeline Steve lived his life in?
Not applicable.
 * No debate: No, but he is supposed to be at the funeral according to the writers.
 * It doesn't serve as evidence outside of the evidence already otherwise contained in Markus and McFeely's comments.
 * Not applicable.

Is there a problem with the time loop explanation, regarding Steve not interfering with historical events?
Not applicable.
 * No debate: In a time loop, it is not possible for Steve to change anything, no matter how hard he tries. It's just not even an option. And even if it was - and it's not - he chose to rest, it wasn't about wanting to change anything. This argument not a problem for the idea of a time loop.
 * This is absolutely not a problem for the idea of Steve not opening a new timeline.
 * Not applicable.

Films (factual)
Unclear.
 * 1953 Peggy Carter: "That was a difficult winter. A blizzard had trapped half our battalion behind the German line. Steve - Captain Rogers - he fought his way through a Hydra blockade that had pinned our allies down for months. He saved over a thousand men. Including the man who would uh, who would become my husband, as it turned out. Even after he died, Steve was still changing my life."
 * Peggy says that her husband is a man who was saved by Steve Rogers. However, this is not evidence against Steve Rogers being her husband, as Peggy would lie in such a manner to cover the fact that Steve is her husband, if indeed that is the case, since time-travelled Steve would be keeping his true identity hidden. Since the same writers, Markus and McFeely, wrote both Captain America: The Winter Soldier and Avengers: Endgame, and it is their intention that this is the case, then it is definitely more than possible.
 * Maybe yes, maybe no.
 * 2014 Peggy Carter: "Mmm. I have lived a life. My only regret is that you didn't get to live yours."
 * Steve looks concerned.
 * 2014 Peggy Carter: "What is it?"
 * Steve Rogers: "For as long as I can remember, I just wanted to do what was right. I guess I'm not quite sure what that is anymore. And I thought I could throw myself back in and follow orders. Serve. It's just not the same."
 * 2014 Peggy Carter: "You're always so dramatic. Look, you saved the world. We rather... mucked it up."
 * Steve Rogers: "You didn't. Knowing that you helped found S.H.I.E.L.D. is half the reason I stay."
 * 2014 Peggy Carter: "Hey. The world has changed, and none of us can go back. All we can do is our best. And sometimes the best that we can do is to..."
 * Peggy starts coughing.
 * 2014 Peggy Carter: "... start over."
 * Peggy coughs and then her expression goes blank.
 * 2014 Peggy Carter: "Steve..."
 * Steve Rogers: "Yeah?"
 * 2014 Peggy Carter: "Wh-? Y-You're alive! You, you came, you came back!"
 * Peggy is presented as having Alzheimer's disease. This would mean that she starts to lose shorter term memories, only remembering more embedded memories, further back. People, tragically, start to forget their spouses and other important memories. It has been suggested by some that Peggy being surprised Steve is alive is a point against the idea that Steve was her husband, but it is more than possible that Peggy in this moment does not remember what happened to Steve beyond her grief after losing him.
 * Maybe yes, maybe no.
 * Steve Rogers: "Yeah, Peggy."
 * 2014 Peggy Carter: "It's been so long. So long."
 * Steve Rogers: "Well, I couldn't leave my best girl. Not when she owes me a dance."
 * It is also even possible, from the, "It's been so long. So long," that Peggy has in fact not entirely forgotten Steve was her husband anyway (if indeed he was). Just that she thinks she hasn't seen Steve, her husband, in a very long time, forgetting recent years of memories, and she's surprised and confused to see him in fact for this reason. Either explanation fits, which makes sense, since the writers of both films wrote at least Avengers: Endgame to fit this way, if not also Captain America: The Winter Soldier, depending on how much they had planned the husband reveal when writing c. 2013.
 * Maybe yes, maybe no.
 * Steve Rogers: "When you were spying on me from across the hall..."
 * Sharon Carter: "You mean when I was doing my job."
 * Steve Rogers: "Did Peggy know?"
 * Sharon Carter: "She kept so many secrets. I didn't want her to have one from you."
 * Peggy kept lots of secrets in her life. It is very possible that her husband's true identity was one of her secrets, keeping him fairly private and lying to cover who he really was, if indeed he was Steve all along.
 * Maybe yes, maybe no.
 * Steve takes four vials of Pym Particles from Hank Pym's office.
 * Steve is shown to take four vials of Pym Particles from Hank Pym's office (and possibly more off-screen), despite only needing two: one for him, one for Tony. There is a possibility that this is foreshadowing, shown because it is Steve taking a pair of vials to later allow himself to jump to the 1940s to live with Peggy, then back to 2023, having made his decision by this point. With the nature of film-making to often seed things like this as a subtle detail to pick up on, it is very possible. In-universe, Steve may have many other reasons for taking more than two vials of Pym Particles. He could be taking several to simply have spares just in case something goes wrong or has gone wrong for any of the others on their missions, because it doesn't make a difference and could be vital. He could be taking several to then allow them to get back and return each of the Infinity Stones, in case they don't manage to bring everyone - including Hank Pym - back. He could be taking two extras in case he needs one to get back from living with Peggy, not sure if he needs it or not. And the thing is, if it were him taking two extras for his intention to live with Peggy, it isn't particularly necessary. Their intention is to bring Hank back, and then they will have an infinite supply of Pym Particles. If they don't successfully bring everyone back, it is hard to believe that Steve would still retire and go off to live with Peggy in the past. So if he's only going to retire if they bring Hank back, then he needn't get Pym Particles there and then - again, it would have to be a "just in case, because why not?", like any other reason he could take more than two, unless Steve did plan to retire even if they fail, or he didn't want to ask for extra back in 2023 so people didn't know about his intention. The nature of film-making would slightly lean it toward the idea of Steve being in an alternate timeline with Peggy, but there are many reasons why it could be anything.
 * Leaning toward yes.

Films (in-universe, the characters might be mistaken)
Leaning toward no.
 * Steve Rogers: "Don't worry Bruce... clip all the branches."
 * And "all the branches" - every branch has to go. This would imply that no branches are left, and therefore Clint's trip and Steve's trip did not open up branches, as those ones can't be closed, nor did just jumping in time cause branches in 1970, 2012, 2013, or 2014 - only the removal of the Infinity Stones, which can be erased.
 * Leaning toward no.

Christopher Markus and Stephen McFeely
No.
 * Stephen McFeely: "I think we're leaning on, when you just take a baseball mitt, you didn't ruin that kid's life. When you took Mjolnir, we accept that that movie happened. Because time is irrefutable."
 * What he says about the baseball mitt, referring to Clint's test run, would imply that Clint did make a change to his child's life. However, that doesn't necessarily mean it is an alternate timeline being created, as if Clint always took that baseball mitt c. 2018, then he took that glove, he still acted even if it didn't create an alternate timeline. McFeely is just saying that that action did not ruin the child's life, with no particular regard to whether it's in the same timeline or a different one. However, he then likens the Mjolnir comment to this, and with the Mjolnir discussion they are talking about an alternate timeline, perhaps implying the baseball mitt is actually an alternate timeline, but also what they are saying about Mjolnir does not particularly make sense, and is all part of a joke response.
 * A different way of interpreting what he says is he is just talking about that Thor: The Dark World still happened in the main timeline as it was because time cannot be changed, thus also meaning that in likening the baseball mitt to it, there isn't any sort of alternate timeline implication. But that doesn't really fit with the discussion being about removing Mjolnir.
 * Unclear, leaning slightly toward yes.
 * Erik Davis: "So people are asking... Does this mean an old Captain America was hanging out this whole time while another Captain America was saving the day?"
 * Christopher Markus: "That is our theory. We are not experts on time travel, but the Ancient One specifically states that when you take an Infinity Stone out of a timeline it creates a new timeline. So Steve going back and just being there would not create a new timeline. So I reject the "Steve is in an alternate reality" theory."
 * Markus is specifically rejecting the Russos' comments in saying he rejects "the "Steve is in an alternate reality" theory", because it is only said that taking an Infinity Stone creates a new timeline.
 * Christopher Markus: "I do believe that there is simply a period in world history from about '48 to now where there are two Steve Rogers. And anyway, for a large chunk of that one of them is frozen in ice. So it's not like they'd be running into each other."
 * Steve just lived through the timeline again, which makes sense for why he would then be on the bench at the end. Markus also smartly says "'48", as this would line up with Marvel's Agent Carter, finishing in July 1947 with no signs of Steve coming back into Peggy's life. 1948 would then make sense, after she and Sousa have presumably broken up.
 * No.
 * Christopher Markus: "... We like your idea."
 * Patrick Shanley: "Really? Alright."
 * Stephen McFeely: "It was our intention that he was always the father of those two children."
 * So, the film is written with the intention that Steve remains in the same timeline when he goes back, creating a predestination paradox where he was always around in hiding.
 * Patrick Shanley: "Awh."
 * Stephen McFeely: "Yeah."
 * Patrick Shanley: "That's very sweet."
 * Stephen McFeely: "But again, there are time travel loopholes for that..."
 * Not exactly sure what McFeely is saying here. If he is saying that there are time travel loopholes which allow this to be the case - you don't need loopholes, the precedent is in the film - or if he means that there are loopholes in that explanation, which isn't completely airtight.
 * Stephen McFeely: "... Or, would require time travel loopholes."
 * It's not clear whether McFeely is correcting himself or making a further comment here. If he's correcting himself, we can ignore the last part.
 * It would seem he is saying that it would require loopholes for this explanation to work, though it does not really. But perhaps he just means loopholes they intentionally built into the film - the explanation about Infinity Stones splitting the timeline.
 * No.
 * Reuben Baron: "Hughes asked about Endgame ' s final scene, in which Steve Rogers travels back in time to live a full life with Peggy Carter. Markus and McFeely and directors Joe and Anthony Russo have provided conflicting answers about whether that occurred within the main Marvel Cinematic Universe or in an alternate timeline. Although favoring the main MCU theory...
 * The writers again favour the main MCU theory.
 * No.
 * Jeff Goldsmith: "I wanna just set the record straight."
 * Stephen McFeely: "Yup."
 * Jeff Goldsmith: "Are there actually two physical Captain Americas living on Earth..."
 * Stephen McFeely: "Oh for...!"
 * Jeff Goldsmith: "... in the same timeline at the same time, so that during the Battle of New York. while hooded Cap is in New York, the other Cap is all the way across the country on pebble beach, having a round of golf with his family?"
 * Stephen McFeely: "Pass!"
 * McFeely acknowledges the disagreement between him, along with Markus, and the directors, joking about how the problem.
 * Christopher Markus: "Okay... Cap doesn't golf."
 * Jeff Goldsmith: "Okay, okay. But are there, are there two Caps on Earth, would you agree to that?"
 * Christopher Markus: "I - there are varying theories... I am much very entertained by that theory."
 * Markus expresses his partiality to the time loop theory, while saying this does not mean it is the only interpretation available or the definitive canon.
 * No.
 * Jeff Goldsmith: "Ray Bradbury's classic time-travel short story The Sound of Thunder sets down a concept many writers have used since - that an alteration in the past can permanently change the future. Does Cap fighting Cap and then not returning to lead a different life with Agent Carter create ripples and problems in the timeline? Were there consequences to what Cap did?"
 * This is poorly worded, but I believe he is essentially just asking whether Cap's actions had some sort of consequence ripple effect on time.
 * Stephen McFeely: "Here's how we reconcile it. We think that there have always been two Caps from 1945 to, say, now, and we just didn't know that. That's the loop, right?"
 * Describing the time loop the writers believe in.
 * Stephen McFeely: "Again, it's not Back to the Future rules, it's branch reality rules. This is not stepping on a butterfly that turns the world into Biff's casino. You can't alter your future by going back to the past."
 * It's a little odd that McFeely talks about the branch realities here again, when that is not particularly relevant to the case they're making about Steve. I would imagine that he's bringing it up simply to mean, "It's not Back to the Future rules, you can't change your past (the only way you can change time is through branches)," to then say that Steve thus wouldn't have changed time.
 * No.
 * Stephen McFeely: "So, his younger self is on ice somewhere and it's only in 2011 that there are technically two Steves running around - to the point where if you were to look closely at Peggy's funeral, there'd be an old man in the back named Roger Stevens."
 * McFeely describes the time loop they believe is in play. All in all, this comment says that you cannot change time, so when Steve went back he simply stayed in time (he didn't remove an Infinity Stone so no branch was created), arriving in 1948 and living through to now. For 63 of those years, his younger self is frozen, so only from 2011 is there two Steves both out in the world.
 * No.
 * Christopher Markus: "And I would like to believe, through some sort of... (bulls**t) "time loop... paradox" - I gotta throw in the words that you use when you're bulls**tting science in a movie - some sort of "quantum paradox", that there are indeed two Captain Americas in the MCU timeline, and that Steve Rogers who looped back into time has therefore always been there, and that he is living somewhere else in the movies you're watching, and what I'd really like to believe is that there's an old man sitting in back at Peggy's funeral in Civil War and that's old Steve Rogers watching young Steve Rogers carry old Steve Rogers' wife up to the front of the church. Can I explain it scientifically? Not really."
 * Markus states his desire for this to be a time loop with Steve, always being in the main MCU timeline. He says it following on from explaining the rules about Infinity Stones, potentially implying that it's because of that. He's then just saying that he would like to think that a time loop makes sense.
 * No.
 * Steve Snyder: "Let's talk about the Cap'n..."
 * Christopher Markus: "Yes."
 * Steve Snyder: "... and the return at the end. And how that related, in terms of, from a science point-of-view."
 * Christopher Markus: "Well what - I mean, we actually have a public disagreement..."
 * Clifford laughs.
 * Christopher Markus: "... with, with our directors. And, you know, it's a playful one...
 * Again joking about the disagreement.
 * Christopher Markus: "... but we are just, Steve [McFeely] and I are just so taken with the idea that Steve [Rogers] went back and somehow therefore has always been back, and got to live his life."
 * The writers really like this idea. Again, not necessarily saying this is the absolute canon, but certainly what they intended with the ending.
 * No.
 * Stephen McFeely: "Chris [Markus] and I are partial to the idea that Steve is part of a strange, unique time loop where he has always been there."
 * The writers discuss again how they feel it should be a time loop with Steve having always been there.
 * No.
 * Stephen McFeely: "The movies you have been watching follow a line where he always goes back.
 * McFeely again explains the time loop, as some people are confused about how Steve "changing" time could not cause a new timeline. But by the writer explanation, Steve didn't "change" time, he merely travelled in time, as this is how time loops work. So he was always there, he was always part of everything we've seen, we just never knew it.
 * No.

Anthony and Joe Russo
Yes.
 * Joe Russo: "If Cap were to go back into the past and live there, he would create a branched reality."
 * Just by going back and living there, he creates a branch.
 * Yes.
 * Xiang Rong: "Peggy Carter was probably already married and in her mid-40s in 1970, in that case what year was it that Captain America went back to dance with her?"
 * Joe Russo: "We can't answer it for now, this is a story that happened in an alternate reality. Maybe it will be revealed in the future."
 * Again, Joe Russo says that Steve's time with Peggy was an alternate reality.
 * Yes.
 * Joe Russo: "He lived a completely different life in that world. We don't know how exactly his life turned out, but I'd like to believe he still helped many others when they were needed in that world. Yes, there were two Captain Americas in that reality..."
 * Joe Russo describes how this is an alternate reality again.
 * Yes.
 * Xiang Rong: "Endgame ' s plot, is it a parallel universe or a closed time loop?"
 * Joe Russo: "Nope, not a time loop."
 * The film's "plot" is referring to the premise of the film revolving around the Time Heist. This is agreed by all parties to not be a time loop. This comment alone doesn't rule out Clint and Steve's jumps being time loops.
 * Unclear.
 * Joe Russo: "For example, the old Cap at the end movie, he lived his married life in a different universe from the main one."
 * Again he says that this is not the main timeline but a different one. Also, even if we are to put stock in Joe's previous comment about decisions, he here says that Steve is an example of a decision splitting the timeline, so the 1940s jump would, even by the decisions interpretation, split the timeline according to him.
 * Yes.
 * Reporter: "At the end of the film, with Captain America deciding to travel back to the 1940s, to a point when the prime version of himself had been frozen, and reunite with Peggy Carter, he created a divergent timeline in which the two marry and grow old together."
 * Again, the Russos say this was a different timeline.
 * Yes.
 * Anthony Russo: "All you can do by going to the past - and for a character like Cap[tain America], living in the past - is create an alternate future. So this is a world in which alternate timelines exist."
 * Captain America lived in an alternate future from the point of his arrival.
 * Yes.
 * Holmes noted that some fans have found it creepy that Steve Rogers essentially made Peggy's future relationship with her husband, as well as their two children, disappear.
 * Russo brothers: "They exist in a different timeline."
 * Again, the Russo explanation.
 * Yes.
 * Travis Clark: "So by that logic, Cap basically created a new timeline for himself when he went back?"
 * Joe Russo: "Correct, so he would have to come back to this timeline in order to hand off the shield."
 * The Russo comment again about Cap creating a new timeline and returning to hand off the shield.
 * Yes.
 * Joe Russo: "That's what Cap does, is, there's an alternate future that happens, so, he would live out that life with Peggy in an alternate future, and he would have to then get back to this timeline to hand off that shield [...] You can imagine, in your own head, another Cap story taking place in that alternate timeline."
 * Here, Joe again makes it clear what his stance is on Cap's story - in going back, Cap created an alternate timeline (seemingly what Joe feels happens in every jump in time in the film), and somehow got back to the main timeline.
 * Yes.
 * Joe Russo: "He deserved to go back to her and to live that life, in an alternate timeline."
 * There's the standard Russo stance being mentioned, that Steve's life with Peggy was in an alternate timeline, not the main one.
 * Yes.
 * Kevin McCarthy: "When Cap goes back..."
 * Joe Russo: "Yeah."
 * Kevin McCarthy: "... where is the Cap in that world? Like, so when he goes back to the early days, is there still another Captain America in that world?"
 * Joe Russo: "Yes, so the way that it would work - right? - is that when Captain America goes back, he would create a branch reality."
 * Kevin McCarthy: "Right."
 * Joe Russo: "OK? Now he would exist in that branch reality with a second Captain America who is frozen in ice."
 * Kevin McCarthy: "So the other Cap still exists in that world?"
 * Joe Russo: "He would..."
 * Kevin McCarthy: "So..."
 * Joe Russo: "... still..."
 * Kevin McCarthy: "... would Peggy..."
 * Joe Russo: "... exist..."
 * Kevin McCarthy: "... not..."
 * Joe Russo: "... but..."
 * Kevin McCarthy: "... know that other Cap?"
 * Joe Russo: "Well he's, that other Cap is frozen in ice at this...
 * Anthony Russo: "And Peggy..."
 * Joe Russo: "... point so..."
 * Anthony Russo: "... understood that he was dead at that point in the storytelling, 'cause Cap went back to a point in time where nobody knew he still was alive, frozen in ice."
 * The Russos insist again that Cap would create a branch reality.
 * Yes.
 * Anthony Russo: "You know, the sort of alternate reality question - I know there's many different theories about sort of how this stacks up and I know Chris and Steve [McFeely] were just talking about some of them."
 * Joe Russo: "Don't go there!"
 * Anthony laughs.
 * They, too, joke about the fact that there's a problem with them disagreeing.
 * Anthony Russo: "Steve [Rogers] could, you know, depending on how - where you go with the alternate realities, Steve can do a lot of things, like he can go rescue Bucky from Hydra. He could get - route Hydra out of S.H.I.E.L.D.. He could go find himself in the ice."
 * Anthony implies that they stand by Steve being in an alternate reality, but also suggests that "where you go" with Steve is still open and this is just one possibility they favour.
 * Yes.

Sean Carroll
No.
 * Aylin Woodward: "Sean Carroll, one of the science advisers on the movie and a theoretical physicist from the California Institute of Technology, told INSIDER that he sides with the screenwriters on this one. Carroll thinks that Cap married Peggy in the existing Marvel Cinematic Universe, not an alternate one."
 * The science adviser says Cap married Peggy in the main timeline, not an alternate timeline.
 * Aylin Woodward: "I think in this case, I see no reason to doubt that [Cap's] in the same timeline. If I remember correctly, when Cap visits elderly Peggy in Captain America: The Winter Soldier, she doesn't say who she gets married to."
 * Carroll being a science adviser and agreeing with the writers is valuable. However, in this part he is voicing his opinion more out of feeling than science.
 * Aylin Woodward: "In the scene Carroll's referring to, we see photos of Peggy and her children, but there doesn't seem to be a father visible."
 * Sean Carroll: "She could've married Cap. That's completely plausible to me."
 * It is unclear here whether, when Carroll says it is "plausible", he is referring to the science/logic of the film fitting it plausibly, or still talking from the perspective of feeling from watching the story.
 * Sean Carroll: "When Cap went back to the 1970s [to retrieve the Tesseract and Pym Particles with Tony Stark], there's a picture of Steve Rogers on her desk. If she married someone else, that'd be weird."
 * Again, more of a feeling statement rather than a statement related to the science/logic of the film.
 * No.

Chris Evans
Leaning toward no.
 * Chris Evans: "You know, I'm not sure I can give you those answers. That's weak as s**t, but ask the writers."
 * Evans believes one should turn to the writers for an explanation, over the directors, though likely did not mean too much by his statement in terms of favouring one side of the debate.
 * Leaning toward no.

Clifford V. Johnson
No.
 * Clifford V. Johnson: "One of the things that I remember asking, would it be possible, when we talked about time travel movies that - or other aspects of science fiction, that I think really works well, is trying to lay in things where you can see that the consequences of the time travel were either implicitly or explicitly there all along, you just hadn't noticed it. And I think there are even aspects of that in the film as well. And..."
 * Christopher Markus: "Well it... We'll get to Captain America at the end of the movie..."
 * Clifford V. Johnson: "Right!"
 * Clifford implies he has seen Captain America's situation as the writers making it so that details that have always been in the films now have a significance as showing that time travel always happened, i.e. a time loop.
 * No.
 * Clifford V. Johnson: "I actually do like examples of stories where you, as long as you never know where the loop is first entered, it's a perfect loop that sits in the story, and it's always there and it would, I think it's an example of..."
 * Kim Griest: "... of "narrative protection"?"
 * Clifford V. Johnson: "Well it's "narrative protection", but I think it's an example of a perfect closed time loop in physics that, that somehow, you know, that has some way of dissipating the buildup that you would get."
 * Science adviser Clifford V. Johnson expresses his partiality to the idea of the closed time loop simply sitting in time, mitigating physics problems.
 * No.

Kim Griest
Leaning toward no.
 * Christopher Markus: "Some people - Anthony Russo yesterday proposed that he went out to the ice, got his frozen self, defrosted himself, and they have like a time share [...] also a valid theory, as far as I'm concerned."
 * Markus addresses the Russos' different theory.
 * Kim Griest: "Well, you know, the multi-world interpretation of time travel which you guys are using, you always have those two things."
 * It's not clear if Griest has understood what Markus is saying, since this part of the discussion is not about multiple worlds.
 * Christopher Markus: "Yeah."
 * Kim Griest: "The Caps are there, and the David Deutsch solution is there's two Caps forever, just like you said, that would be the way that that would do."
 * If Griest has understood, then he is saying that the science would support Markus' theory, but it's not clear if he has.
 * Leaning toward no.
 * Kim Griest: "Yeah, and that's exactly what Deutsch does, but it does require non-unitary quantum mechanics unless you're doing something weird on the Planck scale."
 * Griest seems to imply here that while Deutsch was earlier mentioned to have discussed multi-worlds, he also makes conclusions about time loops. He also says that it requires either non-unitary quantum mechanics or something weird on the Planck scale. Tony specifically says "quantum fluctuation messes with the Planck scale, which then triggers the Deutsch proposition", so this would suggest that because they're messing with the Planck scale, the Deutsch proposition is triggered, which Griest's comments would suggest is the idea of time loops.
 * Leaning toward no.

Jen Underdahl
Leaning toward yes.
 * Jen Underdahl: "So in the case of Captain America, what would a super soldier look like if he had aged 106 years?"
 * Steve was 9713 days old when he went into the ice, and lived a further 4406 days, roughly, from 2011 to 2023. This would make him approximately 14,119 days old when he went back, 38.656. This first comment would suggest one of four things. 1, that Steve is biologically 106 years old, having aged 106 years in his total lifetime. This would mean that approximately 67.844 years have passed for Steve. This would require him to return to 1955 if he were in the singular timeline, which does not work with that interpretation being said to have Steve going back to 1948 or Peggy getting married no later than 1953, unless she remarried and that was a different, previous husband. 2, that Steve has aged 106 years over his lifetime, however long that has been, potentially ageing slower. Compatible for whatever interpretation. 3, that Steve has aged 106 years since becoming a super soldier. 594 days passed between him becoming a super soldier and going into the ice, plus the 4406 days in the present, 4512 days/12.353 years. This would mean roughly 93.647 years to have passed for Steve. This would require him to return to 1930 going by the singular timeline interpretation, which cannot be the case. 4, that 106 years have passed for Steve since he left. This would require him to return to 1917 going by the singular timeline explanation, which cannot be the case.
 * Jen Underdahl: "We shrunk his shoulders and sort of his overall profile to give him that 106-year-old super soldier look."
 * This second comment would then suggest that they mean either 1 or 2. He's either 106 years old, or meant to have the "106-year-old super soldier look" and not necessarily be 106. Since "super soldier" is already an asterisk note in this comment, like she's saying, "He's supposed to have the look not necessarily of a normal 106-year-old, but a 106-year-old who was a super soldier so is still doing physically a little better than most", it seems to be number 1. Not that he's supposed to have an "106-year-old look" and happen to be a super soldier. Plus there's no evidence in the MCU of the super soldier serum slowing ageing. It's not clear how authoritative this comment is, if they were just told "Make him look about 106ish" or if it was a big, calculated number over with the Russos/Marvel, but still, all that said, this comment supports the alternate timeline interpretation, and would mean that Steve lived about 67.844 years in the alternate timeline.
 * Leaning toward yes.

Result
Debatable: '''This is the big one, the big debate. The film itself does not directly provide an answer to this question. The film does indirectly overall seem to lean toward "no", that they didn't open timelines, through what it indirectly presents when thoroughly analyzed for the answers to the other questions that feed into this question. The writers say "no", also clarifying that the film was written with that intent built in. The directors say "yes", and there are certainly points in their favor. Science advisers take the side of "no", Chris Evans slightly seems to lean that way, while the visual effects team seem to be under the impression of "yes". The total evidence does, ultimately, lean toward "no", however, and on top of this, "no" aligns with the answers independently found already to all the relevant questions to this. This explanation ultimately only has one real flaw - why time seems to be changed anyway before Infinity Stones are removed - but it has been explored why this flaw is not resolved by the "yes" approach anyway and why, by necessity, there might need to be some sort of split stretching back to arrival anyway. Ultimately, the "yes" approach carries far more problems/flaws, as well as having less evidence supporting it under thorough inspection. So, overall, it would seem that no, Steve and Clint did not open alternate timelines. Steve was Peggy's husband all this time, living in hiding through the MCU from the 1940s until 2023, once his younger self leaves.'''

Did Steve and Clint open alternate timelines with their individual time travel jumps?
Just new/repaired from this timeline.
 * Debatable: This is the big one, the big debate. The film itself does not directly provide an answer to this question. The film does indirectly overall seem to lean toward "no", that they didn't open timelines, through what it indirectly presents when thoroughly analyzed for the answers to the other questions that feed into this question. The writers say "no", also clarifying that the film was written with that intent built in. The directors say "yes", and there are certainly points in their favor. Science advisers take the side of "no", Chris Evans slightly seems to lean that way, while the visual effects team seem to be under the impression of "yes". The total evidence does, ultimately, lean toward "no", however, and on top of this, "no" aligns with the answers independently found already to all the relevant questions to this. This explanation ultimately only has one real flaw - why time seems to be changed anyway before Infinity Stones are removed - but it has been explored why this flaw is not resolved by the "yes" approach anyway and why, by necessity, there might need to be some sort of split stretching back to arrival anyway. Ultimately, the "yes" approach carries far more problems/flaws, as well as having less evidence supporting it under thorough inspection. So, overall, it would seem that no, Steve and Clint did not open alternate timelines. Steve was Peggy's husband all this time, living in hiding through the MCU from the 1940s until 2023, once his younger self leaves.
 * It would seem that Steve did not leave the MCU, suggesting the shield is just a new/repaired one from this timeline.
 * Just new/repaired from this timeline.

Anthony and Joe Russo
Leaning toward an alternate timeline, if Steve has come back from an alternate timeline. No explicit statements saying this anyway if it isn't an alternate timeline.
 * Reporter: "The question remains how Steve Rogers was able to return to the main timeline decades later, and with an intact vibranium shield to give to Sam Wilson. For Anthony Russo, the concept of the divergent timelines gave the film, and the cinematic universe, multiple layers that he particularly enjoyed."
 * The reporter's phrasing suggests that the reason the shield is intact is because it came from this alternate timeline.
 * Leaning toward an alternate timeline, if Steve has come back from an alternate timeline.
 * Joe Russo: "That's what Cap does, is, there's an alternate future that happens, so, he would live out that life with Peggy in an alternate future, and he would have to then get back to this timeline to hand off that shield [...] You can imagine, in your own head, another Cap story taking place in that alternate timeline."
 * The implication is that the shield is from this alternate timeline.
 * Leaning toward an alternate timeline, if Steve has come back from an alternate timeline.
 * Joe Russo: "... to hand that shield off."
 * Anthony Russo: "Yeah."
 * Again, technically Joe only says he comes back to the timeline so he can hand over the shield, but the way it's said would probably imply that the shield is from this supposed alternate reality.
 * Leaning toward an alternate timeline, if Steve has come back from an alternate timeline.

Result
Debatable: 'Steve seemingly did not leave the MCU'' main timeline at the end of the film, so the shield is just a new/repaired one. No comments ever explicitly said otherwise, anyway. This also makes sense considering the design is slightly different, if it were just the shield from the divergent timeline which wasn't destroyed, it would be identical to the old one.'''

Did Steve and Clint open alternate timelines with their individual time travel jumps?
No earlier than July 1947.
 * Debatable: This is the big one, the big debate. The film itself does not directly provide an answer to this question. The film does indirectly overall seem to lean toward "no", that they didn't open timelines, through what it indirectly presents when thoroughly analyzed for the answers to the other questions that feed into this question. The writers say "no", also clarifying that the film was written with that intent built in. The directors say "yes", and there are certainly points in their favor. Science advisers take the side of "no", Chris Evans slightly seems to lean that way, while the visual effects team seem to be under the impression of "yes". The total evidence does, ultimately, lean toward "no", however, and on top of this, "no" aligns with the answers independently found already to all the relevant questions to this. This explanation ultimately only has one real flaw - why time seems to be changed anyway before Infinity Stones are removed - but it has been explored why this flaw is not resolved by the "yes" approach anyway and why, by necessity, there might need to be some sort of split stretching back to arrival anyway. Ultimately, the "yes" approach carries far more problems/flaws, as well as having less evidence supporting it under thorough inspection. So, overall, it would seem that no, Steve and Clint did not open alternate timelines. Steve was Peggy's husband all this time, living in hiding through the MCU from the 1940s until 2023, once his younger self leaves.
 * It would seem that Steve did not leave the MCU, so he has to have gone back to after Marvel's Agent Carter: Season 2, no earlier than July 1947.
 * No earlier than July 1947.

Christopher Markus and Stephen McFeely
1948. Definitely between July 1947 and December 1953.
 * Christopher Markus: "I do believe that there is simply a period in world history from about '48 to now where there are two Steve Rogers. And anyway, for a large chunk of that one of them is frozen in ice. So it's not like they'd be running into each other."
 * Steve went back to 1948.
 * 1948.
 * Christopher Markus: "... We like your idea."
 * Patrick Shanley: "Really? Alright."
 * Stephen McFeely: "It was our intention that he was always the father of those two children."
 * Steve would then be the husband that Peggy alludes to in 1953, assuming that man is the father of her children, thus meaning he goes back to no later than 1953.
 * Before 1953.
 * Stephen McFeely: "Here's how we reconcile it. We think that there have always been two Caps from 1945 to, say, now, and we just didn't know that. That's the loop, right?"
 * Interestingly, McFeely says 1945 here when they've previously said 1948. 1945 would be problematic due to Marvel's Agent Carter.
 * 1945?
 * Stephen McFeely: "And after he did the last one, he jumped to 1948 and decided to stay."
 * "1948" again. "1945" can be taken as just a slip-up.
 * 1948.
 * Jeff Goldsmith: "Would having a family with Peggy put the world at risk because Agent Carter might not be fighting Hydra as much?"
 * Stephen McFeely: "That dance you see takes place sometime after the second season of Agent Carter."
 * Again, "1945" can be taken as merely a slip-up. This also confirms that the date was intentionally chosen to be after Marvel's Agent Carter: Season 2, the last major chronological appearance of Peggy before bits and pieces through the years, thus meaning there is no conflict with the events of Marvel's Agent Carter with this being the same timeline.
 * After July 1947.

Anthony Russo
Anywhere between February 1945 and December 1953, preferably no earlier than September 1945.
 * Anthony Russo: "If you went back to that timeline, between the point where Steve went into the ice [in Captain America: The First Avenger] yet before Peggy met her husband, Peggy was available."
 * Sounds like if you go by the Russos, Steve went back somewhere between February 1945 (at least September really, since that is when It's Been a Long, Long Time was released) and Peggy meeting her husband, which is no later than 1953, by which time they are married.
 * Anywhere between February 1945 and December 1953, preferably no earlier than September 1945.

Jen Underdahl
Leaning toward 1948.
 * Jen Underdahl: "We shrunk his shoulders and sort of his overall profile to give him that 106-year-old super soldier look."
 * As established, it's likely this means Steve is supposed to be 106, so lived about 67.844 years if in an alternate timeline. If Steve lived approximately 68 years in the alternate timeline, it would make sense for him to have come back when Peggy died (though not immediately after, considering he isn't grieving), presumably around the same time as the main timeline, mid-2016. This would mean that he likely arrived around 1948, suggesting that whatever interpretation of Steve's time travel is taken, 1948 is the year he goes back to.
 * Leaning toward 1948.

Result
No debate: '''Absolutely has to be between February 1945 and December 1953. Taking into account It's Been a Long, Long Time ' s release date, then between September 1945 and December 1953. According to the writers - and considering that it seems that Steve stayed in the main MCU timeline, so it should be after Marvel's Agent Carter: Season 2 - between July 1947 and December 1953. Specifically, according to the writers, and aligning with the rough implication of Jen Underdahl's comment, 1948, which does not contradict anything. So seemingly 1948.'''

Christopher Markus and Stephen McFeely
No.
 * Patrick Shanley: "In Winter Soldier, we establish that Peggy Carter was married and she had two kids."
 * Christopher Markus: "Yes."
 * Patrick Shanley: "We now know that Cap went back in time and married Peggy Carter. Is that the same Cap, was it always him?"
 * Stephen McFeely: "That is... Some conversation to be had on this. Quantum physics works in interesting ways and what Marvel chooses to do is not up to us, but..."
 * It would seem that the writers are not clued in on what Marvel want to do with the grey area of time travel in the film, while they can still express what their intention was and what the film is supposed to express, as it is their writing. So it's been somewhat intentionally left for Marvel to exploit the non-explicit nature.
 * No.
 * Patrick Shanley: "Awh."
 * Stephen McFeely: "Yeah."
 * Patrick Shanley: "That's very sweet."
 * Stephen McFeely: "But again, there are time travel loopholes for that..."
 * One possibility is that he might instead mean that there are time travel loopholes in the way they've written it, intentionally left in there for Marvel to use.
 * Stephen McFeely: "... Or, would require time travel loopholes."
 * It's possible that he just means there are required time travel loopholes in the film that are left in and mean that Marvel could choose to take a different direction.
 * No.
 * Reuben Baron: "... Markus attempted to ease the conflict by calling the issue..."
 * Christopher Markus: "... a question with many answers."
 * This suggests that the question is again not necessarily set in stone, and up for debate.
 * No.
 * Christopher Markus: "And dead is dead, and Loki's dead, except for in that one past reality, which I think has been erased, I don't know."
 * Another comment implying that where Marvel takes things is still open.
 * No.
 * Jeff Goldsmith: "Did you ever decide that there was maybe a moment you were gonna get into the multiverse?"
 * Stephen McFeely: "It clearly exists, right? Because Doctor Strange has talked all about it. I mean that's, it's part of the fabric of that. We may not - this may be where I disagree with Marvel or where they're going, I have no idea where Kevin Feige is going, I don't know what's happening tomorrow, I have no idea."
 * Christopher Markus: "Are you okay?"
 * Stephen McFeely: "But I'm a big believer in stakes, and if you tell me that I can just go and get another Natasha and another Tony and we can keep rolling, then particularly my grandma is gonna go, "Well why did I watch that?" So yeah we are retraining the audience all the time. There may be - I may be wrong 2 years from now where people want, "I want all sorts of stories from people I already lost.""
 * Christopher Markus: "Well particularly in a movie where we are very much heading towards some final resolutions, toward things ending, toward people leaving. If you go, "Yeah but there's seventy-five Tonys out there, like seventy-five billion Tonys out there," your drama is gonna suffer."
 * McFeely comments again how they are not clued in on the future of the MCU, so these are just their intentions and not necessarily the direction of the MCU.
 * No.
 * Jeff Goldsmith: "Did you map out where Loki goes after he grabs the Tesseract in 2012?"
 * Stephen McFeely: "TBD."
 * Christopher Markus: "Probably to cause some havoc in Asgard."
 * Stephen McFeely: "It's probably mischief."
 * Jeff Goldsmith: "But if he has escaped a branched timeline before it was destroyed, would that inspire a new movie that reconciles what Loki does with the Tesseract?"
 * Stephen McFeely: "Listen, we don't work at Marvel, man. I don't know."
 * McFeely reiterates that they are not involved with Marvel's future so do not necessarily have the final world on the canon that will be established.
 * No.
 * Mark Daniell: "At the conclusion of Endgame, Captain America (Chris Evans) goes back to the past and lives his life with Peggy Carter (Hayley Atwell). But 2014's Winter Soldier established that Peggy had a husband and two kids. What does Steve going back in time do to that timeline?"
 * Stephen McFeely: "It depends on what story Marvel wants to tell going forward. I don't know if Marvel wants to tell any more Captain America stories or if Chris [Evans] is up for it. Do they want to tell an alternate timeline story?"
 * McFeely again discusses how the final canon is up to Marvel.
 * No.
 * Stephen McFeely: "To be fair, not everyone agrees with us. I don't even know if Marvel agrees with us. But that's what we think."
 * Again, it's up to Marvel to establish the final canon.
 * No.

Anthony and Joe Russo
No.
 * Anthony Russo: "Part of the beauty of this issue is that really that's what it comes down to in the writers room when we collaborate together. We talk about all the infinite possibilities, we talk about all the different interpretations and versions, but at the end of the day, and this is true for the entire MCU, there are many more possibilities that are discussed that then make their way into the movies themselves. So the text becomes the movie, and then you use that text in the film as a jumping off point for future storytelling."
 * Joe Russo: "It's not defined specifically in [Endgame], it'll be defined by a future movie. Of course, we give rules. I think the rules are also open to debate, clearly."
 * Joe acknowledges the difference in opinion between them and Markus and McFeely, and states, like the writers, that nothing is set in stone yet and it's open to debate.
 * No.
 * Joe Russo: "But we're not really at Marvel anymore, so this is a Kevin problem."
 * Like the writers, the Russos admit they are not involved with Marvel's future.
 * No.

Result
No debate: '''No. None of this is final and set in stone. It's flexible, subject to change.'''