In Avengers Endgame, the following albeit small loop hole is not properly explained:

Whenever Cap and the other avengers go back in time using the quantum tunnel, people said that a new Branched timeline was created which explains scenes like Nebula killing Nebula, the two Caps fighting each other and so on.

So my question is when people say that a new BT is created what do they mean? Does that mean that until people jump using the quantum tunnel, there didn't exist an alternate universe at that point?

Or did the BT always exist in parallel to the main timeline and that Cap and the others just moved to a different time in a different timeline when they jumped?

  • @Paulie_D, ok so when they say created, does it mean that all the events in the main timeline till the time they jumped back just duplicated itself? What I mean to ask is: If Cap jumped back to 2012, do all the events up until 2012 just duplicate itself and form an alternate timeline which they jump to? Because when people say created it kind of gives the feeling that all the characters in the BT just appeared out of nowhere and had no knowledge as to how they came there or came to being
    – penguin99
    Commented May 2, 2019 at 10:58
  • 2
    See the answer below, he covers it pretty well.
    – Paulie_D
    Commented May 2, 2019 at 10:59
  • @Paulie_D, yes but this one little bit is still not explained clearly
    – penguin99
    Commented May 2, 2019 at 11:03
  • 1
    Think of it like tree branch, when the branch is sprouted it doesn't create an entire new tree...does it? So, just the alternative timeline is an exact copy of the old one up to the time it actually branches.
    – Paulie_D
    Commented May 2, 2019 at 11:05
  • Don't try to reason this out, or you will become insane. Look at the only answer and all the comments. Reading those "explanations" reminds me of analyzing a complex Git-repository.
    – Johannes
    Commented Jan 6, 2022 at 0:25

2 Answers 2


Hulk explains it in the movie - he states that you cannot change your past. You can jump into the past (which is effectively your future at that point) and in doing so, you create a new branch of reality (as per the Ancient One, explaining to Hulk). Every time one of the team appears in the past, they branch off the "original" timestream at that point, creating a new reality.

This is why time travel and changing the past does not affect the present time when you come back. There is a whole new reality following forward from the point you visited/changed, and you return to your own time, with the past you experienced completely intact.

These branched timelines will continue on unless they are collapsed back into the "original" timeline, which is the goal in the end where the various stones are returned to their original points, as if they never left.

Cap going back and marrying Peggy is the exception - he left and returned all the stones, thus closing off all the branched timelines (presumably except the 2012 one where Loki pinched the Tesseract and disappeared, probably into a Disney+ TV series) and then he created an alternate timeline where he went to the 40s and stayed there with Peggy. He lived there from that point until he came back to the "main/original" timeline to hand over the shield to Sam.

Time travel is hard and makes your head hurt, but this is as clear as I can understand it!

  • "There is a whole new reality following forward from the point you visited/changed, and you return to your own time, with the past you experienced completely intact." So supposing Cap jumps to 2012, the new timeline starts from the year 2012? Meaning that the events before 2012 never even existed in the branched timeline?
    – penguin99
    Commented May 2, 2019 at 11:02
  • 1
    Meaning the events prior to 2012 match the "original" timeline up to the point at which Cap jumps in. When he jumps back again to 1970, he creates a further branched timeline at that point which carries forward until the stone is returned, at which point it collapses.
    – Dave
    Commented May 2, 2019 at 11:07
  • Oh so every time a stone is returned into that respective timeline, that timeline ceases to exist?
    – penguin99
    Commented May 2, 2019 at 11:09
  • As per the Ancient One's explanation to the Hulk, yes. When the stone is returned to the point it was taken, the black line representing the branched reality collapses back into the orange line representing the original/home reality for the Avengers. The branching is apparently caused by the removal of the infinity stone, and is undone when said stone is returned.
    – Dave
    Commented May 2, 2019 at 11:11
  • So is the branched timeline created when a stone is removed or when they jump using the quantum tunnel?
    – penguin99
    Commented May 2, 2019 at 11:28

The entire Loki Disney+ series is about this.

Yes, new timelines are created via action. They can either collapse back into their “parent” timeline as happened with the ones that Cap fixed, or they can be “pruned” by the Time Variance Authority which exists to keep branches under a certain threshold where they can’t threaten the “sacred” timeline.

At the conclusion of that series Loki and Lady Loki destroy the variant of Kang the Conquerer who set up the TVA and governed the sacred timeline, so now the multiverse and a time war becomes possible.

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