Time Travel

Time Travel is the concept of traveling either backwards or forwards in time from the present date. The time is immutable, meaning that the past cannot be changed and that any attempt to do so will result in alternate timelines/realities.

Time Stone
"The Infinity Stones create what you experience as the flow of time. Remove one of the stones, and that flow splits. Now, this may benefit your reality, but my new one, not so much. In this new branch reality, without our chief weapon against the forces of darkness, our world will be overrun, millions would suffer."

- Ancient One

The time stone has shown to have the ability to rewind time in a given area seeing time unfold. The wielder of the time stone can choose to be unaffected by the manipulation of time from the time stone. Sorcerers such as Doctor Strange can cast spells to make others unaffected by a reversal of time, as he did to Wong at the Battle at the Hong Kong Sanctum. Some sorcerers can have their minds unaffected by the time reversal, and eventually build up the willpower to break free from the spell, as Kaecilius and his followers did, likely due to the power given to them from the Dark Dimension.

Time loops can also be cast. The participants' body will be reset, even if one is killed. Their consciousnesses however will continue on until the loop is ended.

The time stone can also be used to view possible futures (even futures that extend into pasts of other timelines), enabling the wielder to choose the perfect course of action to win their conflict. They can also view these futures at a sped up pace, with Doctor Strange viewing 14,000,605 futures, some spanning up to 5 years, in the space of only a few minutes.

It is also implied by Tony Stark that the time stone may be able to directly affect the past.

Victor Stein's Time Machine
"It can receive visual messages from the future, giving us a glimpse of what life will be like."

- Victor Stein

Using a theory based on interactions between gravity, light and time, Victor Stein created a time machine which was supposed to be able to send messages from the future. Victor tested the time machine with his son Chase, and also he deemed it not functional, the machine did display pictures of the destruction of Los Angeles, which could have occurred because of PRIDE's activities. However, no one saw this alarming message.

Victor later received another message from the time machine, in which he saw a future version of Chase trying to warn him and instructing him not to pick up the Fistigons, in order to prevent Victor from being shot by his wife Janet to protect Chase. However, Victor failed to heed this advice and later attacked Chase with the Fistigons. Later, the time machine once again displayed the same message, and Victor expressed joy at it, taking this as evidence that Chase would survive whatever events involving Jonah were coming.

White Monolith
"Still don't know how I'm supposed to build a time machine." "It's a portal, not a time machine."

- Flint and Leo Fitz

The White Monolith was an artifact which could be used to send a group of people across time. Having been warned by the Inhuman Robin Hinton that a cataclysmic event threatened Humanity, the Chronicom Enoch sent a group of S.H.I.E.L.D. agents into year 2091 with the White Monolith, leaving only Leo Fitz behind, so that they would find a way to avert the catastrophe.

During their stay in the future, the S.H.I.E.L.D. agents recovered a shard of the White Monolith kept by the True Believers in the remnants of the Zephyr One, as well as a machine connected to the shard which they were supposed to use to return into their time. They thus tasked the Inhuman Flint, whose powers were based on geokinetics, to rebuild a White Monolith using the shard they had reclaimed, and then activated both the White Monolith and the machine, thanks to Enoch and Deke Shaw, to return into their time. Although it was not planned, Shaw was also sent into what was the past to him due to being hit by a fragment of the White Monolith.

What remained of the White Monolith after this time travel was destroyed by Melinda May in the aftermath of the Battle of Chicago, thus rendering other time travels through the White Monolith impossible.

Zephyr One
Utilising the type of Time Travel used by the White Monolith, Jemma Simmons was able to modify Zephyr One's Jump Drive to be able to travel in time, bringing Daisy Johnson, Alphonso Mackenzie, Deke Shaw, Melinda May, as well as a group of S.H.I.E.L.D scientists to 1930's New York City.

Quantum Realm
Due to the exotic physics of the Quantum Realm, Tony Stark and Bruce Banner were able to build a time machine for the Avengers. However time travelling like this would not send a person back in time through their own universe, but instead create a parallel timeline. This meant that any changes they made in the past would not affect their own reality. Despite being from a different reality, Infinity Stones taken from a timeline created this way would work in another timeline.

Destruction of Earth
"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."

- Deke Shaw to Quake

Approximately ninety years after the destruction of planet Earth, Deke Shaw claimed that Quake was the one who caused it. When she replied that she was not strong enough to cause such a disaster, Shaw explained a quantum physics theory that for every universe there are infinite parallel universes, implying that she came from the past into the future of an alternate universe and not her own. When the S.H.I.E.L.D. team returned to the past they prevented the destruction of Earth, altering the original chain of events and creating a different timeline.

Time Heist
When the Avengers utilized the properties of the Quantum Realm, following Ant-Man's advice, and created the Quantum Tunnel that allowed them to collect the Infinity Stones years before Thanos and the Snap, they initiated a Time Heist, which involved them traveling to the past and amassing all six Infinity Stones. Hulk, Ant-Man, Iron Man and Captain America were sent back to the Battle of New York in 2012, where Hulk was sent to the New York Sanctum to request the Time Stone. The Ancient One refused, however, explaining that she could not give him the Infinity Stone so Banner could alter his timeline and subsequently leave hers undefended without the stone, although Hulk promised that he would return the stone to her at the exact moment it was taken. After the Battle of Earth, Captain America returns the stones to their proper place in time before their eventual destruction, averting the creation of an alternative timeline or a splinter reality.

Loki's Sudden Escape
However, despite the Avengers' success to return the Infinity Stones into their proper timeline, Iron Man and Ant-Man's failure to obtain the Space Stone that was still contained by the Tesseract, lead to the creation of a new alternative timeline, since the Loki from that timeline was able to get his hands on the Tesseract during an accident at the Avengers Tower, creating a wormhole and successfully escaping his fate of being confined on Asgard, taking moments after his defeat in the end of the Battle of New York. As a result, this past alternative version of Loki has not only avoided getting killed at the hands of Thanos, but precluding the Mad Titan from recovering the Space Stone, thus preventing Thanos from ever completing the Infinity Gauntlet nor cause either the Infinity War or the Snap.

Thanos' Disappearance
During the Time Heist, 2014 Thanos became aware of the Avengers' plan and hijacked the Quantum Tunnel, traveling to 2023 to stop them. In doing so, this created an alternate timeline where Thanos and his forces disappeared from existence in 2014. This means that Thanos never began his campaign to collect the Infinity Stones and cause the Snap, thus sparing countless lives, including the ones that would have been claimed prior to the Snap. This also consequently prevented the formation of the Guardians of the Galaxy, seeing as how Thanos is no longer around to instruct Ronan the Accuser to retrieve the Power Stone, thus there would not be a common enemy for the would-be Guardians to band together against, delaying Ronan's plans of genocide on the Xandarians. However, as the Guardians never came to be formed, it's unknown if this prevented Ego, Star-Lord's father, from from finding his son, as he only found him due to the Guardians' interference in Ronan's plans.

Steve Rogers' Choice
After successfully returning the Infinity Stones back into their proper timeline, Steve Rogers followed Stark's advice to him to get a normal life which Tony Stark had suggested before his death, choosing to travel back to the 1940s in order to live out the rest of his life with Peggy Carter, instead of returning to 2023 as planned, thus creating an alternate timeline. Finally reunited with Carter, he finally gives her the dance he promised her, and the two eventually get married. After his marriage, Rogers retired from his "Captain America" moniker, but would continue to help out when he was needed in his new timeline. Having grown old from his retirement, Rogers eventually visits Sam Wilson back in 2023, entrusting him with his shield and choosing him as his successor.

Time Travelers

 * Phil Coulson †
 * Melinda May
 * Jemma Simmons
 * Daisy Johnson/Quake
 * Alphonso Mackenzie
 * Yo-Yo Rodriguez
 * Leo Fitz † (alternate timeline)
 * Deke Shaw
 * Enoch
 * Phil Coulson (Chronicom Life-Model Decoy)
 * Scott Lang/Ant-Man
 * Clint Barton/Hawkeye
 * Steve Rogers/Captain America
 * Tony Stark/Iron Man †
 * Bruce Banner/Hulk
 * Natasha Romanoff/Black Widow †
 * James Rhodes/War Machine
 * Nebula
 * Rocket Raccoon
 * Thor
 * Nebula † (alternate timeline)
 * Gamora (alternate timeline)
 * Proxima Midnight † (alternate timeline)
 * Corvus Glaive † (alternate timeline)
 * Cull Obsidian † (alternate timeline)
 * Ebony Maw † (alternate timeline)
 * Thanos † (alternate timeline)

Behind the Scenes

 * Joe and Anthony Russo went to great lengths in Avengers: Endgame to make the audience understand that time travel does not work in the Marvel Cinematic Universe as it does in , which has informed many people's understanding of the mechanics of time travel. Clifford V. Johnson and Sean M. Carroll served as consultants on the film to create a version of time travel that was true to real-life theoretical physics.