We have a lot of questions about it as well, and the filmmakers’ conflicting answers on how it all works has us scratching our heads. But that said, we think we understand it… more or less. Let us guide you through it all below…
As we long suspected would be the case, yes, the Avengers use time travel in order to undo Thanos’ Snap heard round the universe. And while the circumstances of how that time travel play out might be different from what many fans had theorized, the end result is the same: The Mad Titan is defeated and everyone who was lost in the Decimation is returned, albeit after five years of non-existence.
But how exactly does the time travel work in Avengers: Endgame? Basically, it’s super-confusing — no, we’re not gonna start explaining what a Mobius strip is here — and it seems like the filmmakers purposely avoid fully explaining it in the film, instead opting to point out how it doesn’t work. That said, let’s put on our Quantum Realm Suit, adjust our time GPS, and time-heist this thing!
The Quantum Realm
The key to time travel is revealed once Scott Lang escapes from the Quantum Realm, where he was stuck for five years ever since the end of Ant-Man and the Wasp. Time operates differently there, and for Scott it seemed like he was only gone for five hours. So he takes this info to the Avengers, since he’s better at the “heist” part of a time heist and needs a big brain to figure out the “time” portion of things.
At first, Tony Stark isn’t interested in pursuing the matter, as he thinks it was dumb luck that Scott made it out of the Quantum Realm at all. So Captain America and Black Widow bring Ant-Man to the Hulk, who agrees to give it a go… even if it isn’t exactly his area of expertise.
Time Travel Doesn’t Work That Way!
Eventually “Professor” Hulk comes in to help figure out how to use Scott’s discovery to send the Avengers back in time. And while everyone has their own idea of how to go about the mission, Banner reminds the group that time travel doesn’t really work the way it does in movies such as Back to the Future or The Terminator (or Time After Time or Somewhere in Time or Timecop…). War Machine suggests just going back in time and killing Baby Thanos, a twist on the old killing Baby Hitler concept, but again, that’s “movie time travel.” Or so we’re told.
According to Banner, you can’t just go back in time and change the past in order to alter the future. Because the future is already your past! You can’t change the future, because if you did, you wouldn’t be the same version of yourself who time-travelled in the first place to make that change. See, it’s confusing.
Instead, any change to history will create an alternate, or divergent, timeline. Say you did kill Baby Thanos. That wouldn’t affect the Thanos in the MCU timeline that already saw him cause the Decimation. Instead, it would just create a parallel reality where Thanos died as a baby. But the world of our heroes would remain unchanged. So what to do then?
Here’s where we get to the time heist, as Tony Stark can’t help himself and basically figures out how time travel works when he has a few hours of spare time one evening. He joins his old teammates, who have been kinda/sorta getting there, though Scott Lang narrowly avoids being permanently turned into a child/baby/old man in the process, and definitely wets himself along the way. The Hulk is smart, but Stark is needed for this one.
Soon enough, the plan is hatched to send three teams back to various points in time/space in order to retrieve each Infinity Stone from a time before Thanos had them. The Avengers will then take them back to their present time of 2023 (five years after the Snap) and use them to undo the Decimation with a new Snap. But as the Ancient One explains to Banner during the Battle of New York back in 2012, removing one of the Stones from their timeline will cause said timeline to splinter off into the divergent realities mentioned above. The Stones being together, presumably in the same time if not in the same specific place, keeps the timeline intact. That’s why, once the Avengers finish undoing the Decimation in 2023, they must return the Stones to the exact moments they took them from the past. That way the Stones will not truly leave their respective past points, and hence not alter the timeline.
And that’s what Captain America apparently does with each of the Stones at the end of the film, returning them to their rightful places in the past. Though he takes a 70-year break or so along the way. Speaking of which…
Despite the goal of not altering history, it seems that’s what happens anyway, as the Nebula of the present’s mind and memories mix with those of the Nebula of the past. This allows the Thanos from around the time of Guardians of the Galaxy 1 (in 2014) to see the future, including his own death at the beginning of Endgame and the Avengers’ time heist plan. And so he travels into the future to the “present” of Endgame, in 2023, which leads to the film’s final confrontation and Iron Man’s death as he snaps Thanos and his army out of existence.
But! How could the Thanos of the past be killed in Endgame, since now he will never be able to find the Infinity Stones, put them in the Infinity Gauntlet, and wipe out half of all life in Infinity War, leading to the Avengers coming up with the time heist plan as a result? Unless this Thanos is from a divergent timeline, created by the fact that history was altered when the Avengers travelled to the past (and Nebula inadvertently revealed the future to Thanos). Which, Endgame previously told us, should not happen as long as the Infinity Stones don’t leave their place in the timeline. Either that or the Ancient One’s dialogue to this effect was just too vague or unclear about the possibility of divergent timelines being created…
The same question applies to the Gamora of the past, who didn’t die on Vormir and is seemingly alive and well at the end of Endgame, with Star-Lord preparing to go find her in space (Guardians Vol. 3 plot line?). If she’s living in the present, how can her future self have died in the past when Thanos sacrificed her for the Soul Stone? Divergent timeline, that’s how.
The Loki who escapes with the Tesseract right after the Battle of New York is another big question that comes out of the Avengers’ time travel shenanigans, since not only did he disappear into a portal to points unknown, but he also took the Space Stone with him. That’s why Cap and Iron Man had to go back even further to the 1970s to find another instance of the Tesseract that they could steal. But by the end of the film, when Captain America returns all of the Stones to their rightful place (off camera), there’s no way he could’ve returned the one that past Loki made off with. Perhaps we’ll learn more about this in the Disney+ Loki show, but it sure seems like that’s another divergent timeline right there.
And then there’s Cap, who winds up living out his life with Peggy Carter in the past. This conflicts with what we know to be Peggy’s history in the MCU, as she married a man who Cap saved during World War II, a man with whom she had children. If Cap and Peggy got together in the past, then that aspect of her history would have to be altered… creating a different timeline. (Though, yes, one could argue that Steve Rogers was always the guy she married and that he and Peggy basically kept that info hidden for 70 years. But really, that’s a stretch.)
Update #1: The directors of Avengers: Endgame, Joe and Anthony Russo, have addressed the time travel in the film while talking to EW. According to the pair, Captain America did in fact live out his days with Peggy in an alternate timeline. “If Cap were to go back into the past and live there, he would create a branched reality,” Joe Russo told the site. “The question then becomes, how is he back in this reality to give the shield away [to Falcon at the end of the film]?”
The brothers go on to imply that there may be more to Cap’s story that is yet to be revealed. “Maybe there’s a story there,” Joe said. “There’s a lot of layers built into this movie and we spent three years thinking through it, so it’s fun to talk about it and hopefully fill in holes for people so they understand what we’re thinking.”
It’s also worth asking how the elderly Cap made it back to the “main” MCU timeline at the end of the film if he lived out his years in a different reality. Did he somehow stumble upon tech that allows him to traverse realities as well as time?
The Russos have also confirmed that Bucky knew what Cap was going to do before he left for his fateful time-travel trip to find Peggy. And the Falcon didn’t know. EW also raises the question of where Cap got the shield from that he gives to the Falcon when he passes the Captain America torch to him (remember, Cap’s shield was wrecked by Thanos). Could it be that he knew a Falcon who became Captain America in the reality where he lived out his life with Peggy, and that’s where the shield came from? Of course, there’s a Falcon and Winter Soldier show (let’s just start calling it Captain America and Bucky) coming to the Disney+ streaming service. It sure seems like clues have been dropped here which will be picked up there…
Update #2: The Russos and Endgame screenwriters Christopher Markus and Stephen McFeely don’t appear to be on the same page. In a separate recent interview with Fandango, the writers rejected the theory floated by the Russos. IGN has reached out to Disney for clarification on which party has the official and final say on the matter.
The Bottom Line
So what can we definitively say about time travel in Endgame? It’s clear now that, as the Hulk pointed out, changing the past won’t change the characters’ futures. But beyond that, it seems that, despite the team’s best efforts, at least some divergent timelines were formed. All of which brings us back to the beginning, when we said that time travel in the MCU was confusing. But aside from what may just be some needlessly misleading dialogue from the Ancient One, and thanks now to some confirmation from the Russos, it all basically fits together… while also leaving the door open to be further explored in future MCU properties. Make mine the multiverse!
What do you make of the MCU’s take on time travel? Let’s discuss in the comments!
Talk to Executive Editor Scott Collura on Twitter at @ScottCollura, or listen to his Star Trek podcast, Transporter Room 3. Or do both!