The filmmakers behind Avengers: Endgame painted themselves into a pretty tight corner with the conclusion of the movie’s predecessor, Avengers: Infinity War. The Mad Titan Thanos managed to get all the Infinity Stones together, and with a snap of his fingers, erased half the life in the universe from existence. But this is the Marvel Cinematic Universe, and the heroes always had to make an attempt at undoing the damage Thanos did. The question was: How could they?
The answer, as we now know, is time travel. But time travel is confusing in movies (not to mention theoretical physics) on the best of days, when you’re not dealing with space magic that can rewrite the rules of reality on top of it. It’s so confusing, in fact, that it seems like the directors and writers of Infinity War and Endgame have differing (and mutually exclusive) ideas of how it works.
Speaking with Entertainment Weekly, directors Joe and Anthony Russo described time travel in Endgame as creating alternate timelines–essentially, every time the characters return to the past, the changes they make to the past createnew, complete universes with new events, with the original universe staying intact and unaltered. That’s how the Avengers can go back to, say, the Battle of New York and accidentally release Loki. It creates a new timeline where Loki didn’t go back to Asgard, as he did in the original MCU timeline (depicted in Thor: The Dark World). The timeline were Loki is loose with the Tesseract in 2012 is its own separate universe, and the Avengers are able to travel between them somehow. This roughly matches up with how Bruce Banner explains time travel within the movie itself, so that’s good so far.
The Russos use that model of time travel to explain Captain America’s ending, one of the more confusing and controversial events of the movie. At the end of the film, Cap goes back in time to return the Infinity Stones to where the Avengers found them, but he stays in the past to spend his life with Peggy Carter, the woman Cap has said was the love of his life.
The time machine seen in the movie is less about getting people to the past, it seems, and more about helping them find their way back to their original universe, the one we’ve been watching in the MCU all along. But that raises the question: If Cap was in another timeline, how did he get back to the original timeline to give Sam Wilson his shield at the end of the film? The Russos covered that question in their EW interview, without giving a definitive answer:
“If Cap were to go back into the past and live there, he would create a branched reality. The question then becomes, how is he back in this reality to give the shield away?” Joe Russo asked with a smile. “Interesting question, right? Maybe there’s a story there. 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.”
We also know that Peggy was married and had kids while Steve was supposed to be frozen in a glacier, so wouldn’t Cap’s presence in her life fundamentally change those events?
The Russos agree that that’s true–but the Peggy Cap ends up with is in another timeline, which is how you get around the ethical questions that fans have raised about Cap wrecking Peggy’s family for the sake of his own happiness.
“If you went back to that timeline, between the point where Steve went into the ice [in Captain America: The First Avenger] yet before Peggy met her husband, Peggy was available,” Anthony Russo said in yet another interview, this time with The Hollywood Reporter. As for Peggy’s family, “They exist in a different timeline,” the directors said. So Cap didn’t erase her family in the original timeline, just the new one, which is maybe better, because they technically still exist somewhere?
Anyway, the way the Russos explain time travel is the way we interpreted it in Endgame as well (and really, it’s the only way it makes sense). But Stephen McFeely and Christopher Markus, the movie’s writers, have a totally different take. The pair gave an interview to Fandango, in which they explained the movie’s time travel as being completely different. Instead of a lot of new timelines and alternate realities created by each of the changes the Avengers make when they travel through time, the writers said that only removing the Infinity Stones creates branches–which is similar (and similarly confusing) to what the Ancient One told Bruce Banner during the movie.
“We are not experts on time travel, but the Ancient One specifically states that when you take an Infinity Stone out of a timeline it creates a new timeline. So Steve going back and just being there would not create a new timeline,” Markus said. “So I reject the ‘Steve is in an alternate reality’ theory. I do believe that there is simply a period in world history from about ’48 to now where there are two Steve Rogers. And anyway, for a large chunk of that one of them is frozen in ice. So it’s not like they’d be running into each other.”
So Markus and McFeely say that Cap could just be in the past, living his life, and that his presence would not change the timeline–and therefore, he could just show up in 2023 to give the shield to Sam. That doesn’t seem to account for issues like Loki escaping with the Tesseract or Cap pretending to be a HYDRA agent, but it seems like the movie attempts to explain that with the conversation with the Ancient One: essentially, the Infinity Stones are magic, and since they create “the flow of time,” it’s impossible for alterations to mess up the timeline. Or something.
Lost? Yeah, us too. Maybe the overall point is that time travel is a beast for even talented Hollywood writers and directors to tackle, and trying to add it to something as huge and unwieldy as the MCU was even tougher. But while time travel might add an element of logical weirdness to Endgame, it seems like the greater MCU going forward will have something different to contend with, from what we saw in the latest trailer for Spider-Man: Far From Home. That’s the idea of multiple parallel universes, something that’s straight out of Marvel Comics (not to mention last year’s Spider-Man: Into the Spider-Verse). Here’s hoping it doesn’t get too confounding.