After Thanos snapped half the universe out of existence at the end of Infinity War, fans speculated about how - not if - the Avengers would bring everyone back. How could they without the Infinity Stones? In Avengers: Endgame, the Earth’s mightiest heroes travel back to different points on the MCU’s timeline to revisit some pivotal moments and swipe the Infinity Stones. The time heist in the middle of the movie is a lot of fun, but does the time travel in Avengers: Endgame actually work?
There are huge surprises in Endgame, with a surplus of characters showing up in unexpected places. Narrative twists are to be expected from a Marvel movie; however, in this case, they're facilitated primarily by time travel. This offers characters the chance to visit places - and times - typically reserved for fan fiction. Perhaps the weightiest of these twists comes toward the end when Steve Rogers not only travels back in time, but also stays there in order to marry the love of his life, Peggy Carter. It's a cathartic moment, but does it make sense? Assuming your brain hasn't melted trying to figure out the internal logic on your own, this look at Endgame's time travel rules should make for a handy guide.
The Thanos That Perishes At The End Of The Movie Is From A Parallel Universe
Partway through Endgame, a major problem arises: Thanos shows up to claim the Infinity Stones and create a new world in his image. But technically, it's not the same Thanos who snapped half the galaxy out of existence; this is a Thanos from a divergent timeline.
This Thanos is presumably the same version from Infinity War. He likely realized it was possible to travel to the future when he learned that War Machine and a new version of Nebula were trying to grab the Power Stone. This realization affected his behavior and subsequent decisions, changing the timeline and creating an alternate version of Thanos.
Time Travel Relies On The Quantum Realm
To time travel in the MCU, you have to use either the Time Stone or the Quantum Realm. Barring some divergent timeline in which everyone has a Time Stone, the Avengers have to shrink down and travel through the Quantum Realm to go from point to point.
Unfortunately you can't just hop into the Quantum Realm and end up at the Battle of New York; you have to use Tony Stark's "reverse mobius strip" map of the QR, which spits you out at a specific point in time and allows you to return exactly when you left.
The MCU Timeline Is Secure
With time travel now in the mix, it's reasonable to wonder if the entire MCU timeline has been irrevocably altered. Fortunately, that's not the case. All the moments you love from Phases 1 through 3 are preserved in amber.
Everything that happened in the past still occurred to make the characters who they are in Endgame. As Bruce Banner explains, their reality exists linearly, even if they aren't moving through time in a linear fashion. This means Thanos is always going to snap half the universe away, and the Avengers are always going to bring it back.
You Can Talk To Your Past Self Without Creating A Paradox
One of the classic rules of time travel - largely popularized by Back to the Future - is that you shouldn't talk to an earlier version of yourself. This paradox can have dire consequences. In the MCU? Not so much. In Endgame, characters not only have conversations with their older selves, but in the case of both Captain America and Nebula, they also get into full-on brawls with their previous iterations.
Because Nebula and Cap aren't actually fighting previous versions of themselves, but rather alternate versions of their previous selves, no one disappears, or explodes, or does whatever else we've come to expect from a time travel paradox.