Multiple timelines in Avengers Endgame

Question

In the original timeline, Thanos fights infinity war and won in 2018. But if Thanos travelled to future in 2014 to 2023, shouldn't it create different timelines in which:

1. Thanos is not there at all from 2014 because he went in a time machine and never returned, and another time line where:

2. Thanos traveled to 2023 from 2014 and met the Avengers and lost. Ironman died in this timeline. Infinity war can't happen here.

3. And the original timeline where Thanos didn't time travel in 2014, infinity war happened, people died, Thanos got beheaded, Avengers retrieved stones, and hulk snapped fingers to bring back the vanished ones.

If restoring infinity stones to their original timeframes, nullifies all timelines other than the last one, then how can Ironman die?

Answer 1

Restoring Infinity Stones doesn't mean all time-lines will converge.

It just prevents them from diverging a lot, since each universe/time-line requires the stones for stability. The directors give the example of CA going to another time-line to live with Peggy before returning to this one.

The time travel in this movie created an alternate reality. [CA] lived a completely different life in that world. [...] 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.

The multiple timelines in the movie all have different stories now. Here are some examples:

• Main time-line, Avengers 2023: The one we've seen in all the movies so far.

• GotG, 2014, Thanos vanished: The one where they take Soul and Power stones from, Thanos leaves that one (to join the main one), and Infinity War never happens.

• Avengers, 2012, Loki steals Tesseract: The one where they went to New York, took the staff with the Mind Stone, and the Time Stone, and let Loki run away with the Tesseract. Loki isn't imprisoned in this one, who knows what might happen.

• Asgard, ?, Thor takes Soul Stone and Mjollnir: Possibly doesn't diverge much, since both are returned, but the Soul Stone will probably not infect Natalie Portman again, so there will be some differences

• Earth, 1940, Rogers marries Peggy: CA goes back to live his life with Peggy, before returning to the main time-line.

Our main heroes will still follow their main timeline, as will we, the viewers. This article lists a few time-lines. This question also shows a cool graph:

What the Ancient One explains is that

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 branched reality, without our chief weapon against the forces of darkness, our world will be overrun. Millions will suffer.

She is giving an example of how a new timeline is created when something different happens (in this case, taking a Stone). Bruce then shows her that they will return the stones to try and keep everything similar. But obviously some timelines need to change, since in one of them, Thanos vanishes and never returns. In that timeline, logically, the snap never happens. Taking the Stones causes new timelines, but so does changing other things. The Ancient One gave an example based on what Bruce was asking of her, to take the Stone.

Answer 2

Here's a statement from Russo Brothers themselves.

Q: [Endgame’s] plot, is it a parallel universe or a closed time loop?

A: 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.

source: https://bgr.com/2019/04/30/avengers-endgame-ending-russo-brothers-on-captain-america-iron-man/

Let's address that Back To The Future confusion first. As to why they say it's all bullsh*t and then do something very similar to what Marty and Doc did - sneaking in the backdrop of a prequel.

In BTTF, when you go back in time, you don't create a parallel alternate timeline. If you goof up, you replace the original timeline with the alternate version. When Biff changes the past, the future is re-written, the original timeline has been erased leaving only the new, alternate timeline. So they go back in to the past to fix stuff. Once they do, they once again re-write the timeline with a corrected version. At any given moment only one timeline exists. And this gives rise to the Grandfather Paradox.

In the Endgame, traveling back to the past means going back and creating an alternate timeline which lives along side the original timeline. The original timeline is not re-written with the alternate version. Removing stones is one way to create an alternate timeline. But there are other ways to create them.

Every decision you made in the past could potentially create a new timeline.

For example, the two Nebula's interfering creates a new timeline, this is well before they go near the Power Stone. 2014-Thanos gets to know the future (that 2023-Nebula is from) and this creates an alternate timeline. Even if Steve returned the Power Stone, that wouldn't be enough to make this timeline vanish.

Now to the questions. (Let's call the Original Timeline T0, and 2014-Thanos is from Timeline T1)

Thanos is not there at all from 2014 because he went in a time machine and never returned, and another time line where:

The Original Timeline, T0, has already had Infinity War, 2014-Thanos leaves T1 and reaches T0 in 2023 where he's killed. In the end, if Steve returned the Power Stone to T1, that timeline will have an alternate future without Thanos. Perhaps Ronan will get his hands on the stones, we don't know, and it is out of the scope of this film (just like Loki who disappears with the Tesseract).

Thanos traveled to 2023 from 2014 and met the Avengers and lost. Ironman died in this timeline. Infinity war can't happen here.

2014-Thanos traveled from T1 to T0 and to the year 2023. T0 has already seen an Infinity War. T1 might see an infinity war, but it's not caused by Thanos because he's killed in T0. Iron man of T0 is dead, we don't know the fate of Iron Man in T1.

And the original timeline where Thanos didn't time travel in 2014, infinity war happened, people died, Thanos got beheaded, Avengers retrieved stones, and hulk snapped fingers to bring back the vanished ones.

Original Timeline is T0, where the snap happened in 2018 and was undone in 2023. After that, a 2014-Thanos shows up from T1 and is killed of, thereby not interfering with T0's past. Iron Man, Gamora, Vision, Black Widow and everyone who was killed for reasons other than the "snap", remain dead.

Answer 3

Ok here's how I understood it. The time travel explained in the Endgame involves traveling to different timelines of the same reality. When they choose to travel back(or future?) to 2012, 2013 and 2014, they actually went to different timelines of the same reality. That means events are going to unfold exactly same as the original timeline in all those timelines as well. As the ancient one explains to Hulk that infinity stones maintains the flow of time in those realities, taking a stone will create a divergent timeline which may result in catastrophic outcome to all those inhibiting that timeline. But as Bruce Banner puts it, if they returned the stone to the exact moment in the history then all those divergent timelines can be erased. When War Machine and Nebula took the stone from Morag in 2014, that created a divergent timeline in which Thanos travels to the future, that is, to 2023. Where he fights with the Avengers. At the end Iron Man killed Thanos with the Snap and died in the process. The Thanos that died is the one from that 2014 timeline. When Cap returned the stones to their original position, that divergent timeline where Thanos travels to 2023 got erased and he never traveled to 2023. Infinity war still happens in that timeline but that doesnot effect the original timeline of Endgame. In our original timeline, the snap is reversed, Iron man dies and everyone comes back to life.