Avengers: Endgame timeline and causality [duplicate]

Question

In Avengers: Endgame,

if Thanos from 2014 was dusted in 2023 by Iron Man's snap, then how did the Thanos other 'snap' in 2018?

Does this imply that

there is a branch reality where they never bring back everyone with Professor Hulk's snap.

Answer 1

What Professor Hulk meant by his long speech in the lab is, traveling into the past creates a new reality; the old one still exists. Thus, the Grandfather Paradox can't happen. This is not the same as most Star Trek time travel stories, or Back to the Future.

The 2014 Thanos that was killed in 2023, is NOT the SAME Thanos as the one who did the Snap; in the reality the 2014 Thanos was from, the Snap would never happen so there would be nobody to save. The hard thing to understand is, somehow Tony Stark figured out how to bring the Avengers back to their original reality when they traveled forward. Thus, the Infinity gems were brought to the reality where the Snap had happened, and they could be used to undo it. So, it's like this. There was a Thanos in the reality in which the time traveling didn't happen. He's the one who gathered all the Infinity Gems, did the Snap, killed half of everybody. Then he disintegrated the stones, and got his head chopped off by Thor. Five years later, the remaining Avengers travel into the past, thus creating a different reality, where a different version of Thanos finds out about their plans. The Avengers return to their original future, which was still affected by the first Thanos we knew about. Then the bad Nebula pulls the second Thanos across realities into the one where half of everyone is dead, and the latter part of the movie occurs.