Thread:Elledy92/@comment-26838855-20190425183005/@comment-28529249-20190724205251

The Wikia Editor wrote:

As for how branch timelines are created, the rules in the comics are that, if the time traveler doesn't make any significant changes to the past (such as stopping oneself from traveling back in time in the first place), then it simply remains a single timeline, as nothing of note was changed.

However, if something significant IS changed, then it results in an alternate timeline, which will continue to exist independantly of the original timeline.

A time traveler showing up does not necessarily, in an of itself, change the timeline. That's not how it works in the movie though. If I recall correctly, according to the Russos, every time you travel to the past, a new timeline branch is created. While according to Markus & McFeely, time is only changed if you mess with one of the infinity stones, otherwise it's the predestination paradox.