Avengers: Endgame (2019) poster. Image: Marvel Studios
Making sense of Avengers: Endgame most fascinating–but very confusing–plot device, and how it (mostly) stays consistent throughout. Spoilers are ahead for this movie.
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If you’re reading this, you’ve more than likely seen Avengers: Endgame (and if you haven’t, best that you go see it first and then come back here, because there’s going to be Heavy Spoilers). Like many in the theatre, you laughed, cried, and cheered at all the right moments, looked at what happened on-screen in awe, and maybe even clapped when it was over. Yet as you left the theatre, talking about it among your family and friends, a troubling thought occurred to you, one that just wouldn’t go away. That thought was, “That was great…but it didn’t make any sense!”
And you can sum up why it didn’t make sense in just two words: time travel.
Yes, Avengers: Endgame uses one of the coolest, but baffling, scenarios in all of science fiction. All of us, at some point or another, imagined going back or forward in time, whether it be walking with the dinosaurs, meeting our own ancestors, or witnessing what will happen a century from now first hand. Yet, as we know–or think we know–from countless novels, movies, video games, and television shows, the act of going back to the past or the future isn’t as simple as it sounds. There are rules, and very complex ones at that.
Endgame isn’t any exception; in fact, it may have some of the most complex rules of time travel in any mainstream movie. Not to worry, though, because we’re going to try to explain how traveling from one point to another works in this movie. Thus, if you watch Endgame a second time, you’ll have a better understanding of what’s going on, and why it actually doesn’t violate its own rules…or at least ninety percent of them, anyway.
Why the Ant-Man movies are more important than you thought
Who would’ve thought that, at the end of Avengers: Infinity War that Scott Lang (Paul Rudd) of all people held the key to undoing Thanos’ (Josh Brolin) snap? It also turns out that watching Ant-Man (2015) and Ant-Man and the Wasp (2018) are actually essential for understanding the most easy-to-understand aspect of Endgame’s method of time travel.
As shown in the Ant-Man movies, there exists a subatomic universe called “the Quantum Realm,” where “all concepts of space and time become irrelevant.” Simply put, time moves at different rates in the Quantum Realm than it does in our own universe. One hour spent there could mean an entire year has passed by in our world. This explains how, in Endgame, Scott wound up five years in the future even though he only spent five hours in the Quantum Realm. It also means that, because the Quantum Realm is a universe composed of infinite space and time, you could travel to any place or any time in the known universe.
Of course, the only way one can enter the Quantum Realm is to shrink down in size using “Pym Particles.” That’s problem number one. Problem number two is that, once you enlarge yourself, there’s no guarantee where or when you’ll end up. Hence why Tony Stark (Robert Downey Jr.) had been secretly inventing a special GPS to navigate through the Quantum Realm to prevent his fellow Avengers from becoming lost. Problem number three? You better be sure you’re not affected by the Quantum Realm or, like Scott found out first-hand during the time travel tests, you could end up as a baby or an old man.
In short, we might also call the Quantum Realm the “MacGuffin Realm.” All you really need to know, however, it’s the mechanism which makes time travel possible in Avengers: Endgame. The real fun begin when you go over the rules of Endgame’s method of time travel.
Marvel Studios’ AVENGERS: ENDGAME..L to R: Nebula (Karen Gillan) and Captain America/Steve Rogers (Chris Evans)..Photo: Film Frame..©Marvel Studios 2019
Why you cannot change the past
I’m sure many of you saw time travel the same way Scott Lang, Rhodey Rhodes (Don Cheadle), and Clint Barton (Jeremy Renner) did. After all, every single time travel movie out there “proves” that changing the past changes the future. So why not, as Rhodey suggests, couldn’t they just kill Thanos before he takes the Infinity Stones? Also, doesn’t taking the Infinity Stones and bringing them into the future before Thanos gets a hold of them also prevent him from erasing half the universe?
Not so, according to Professor Hulk (Mark Ruffalo). As it turns out, whatever you do in the past has no effect on the future whatsoever. In fact, according to Professor Hulk, that method of time travel is scientifically impossible.
Let’s suppose the Avengers did prevent the snap from happening by taking the Infinity Stones before Thanos gets them. This would mean that if the snap never happened, the Avengers wouldn’t also go back in time because the reason for doing so no longer happened. But if they didn’t go back in time, then it means the past remains the same and the snap still happens. In other words, you’d have two things which both happened and didn’t happen simultaneously. And if this sounds a lot like Schodineger’s Cat, that’s precisely what this paradox this would create.
Moreover, everyone, including time travellers, experiences time as a linear, forward progression which cannot be changed. From a time traveller’s perspective, then, travelling back in time is something they’ve already done, experienced, and cannot change. Whatever future actions they make in the past also, from their perspective, hasn’t happened yet. Or, as Professor Hulk puts it, “If you travel into the past, that past becomes your future, and your former present becomes the past which now can’t be changed by your new future. (i.e. the past).”
Thus Endgame shows that when the Avengers are travelling through time, what they’re actually doing is travelling into a parallel universe to a different time in that universe. This concept of time travel has basis on what’s known in quantum mechanics as the many-worlds interpretation. As postulated by physicist Hugh Everett III, the idea is that there’s an infinite number of possible universes, each one created by different outcomes. For example, if you flip a coin and it ends up heads, there’s another universe where it came up tails.
What this basically means is that the very act of you travelling into the past creates a new reality, one which branches off from the point where you first arrived. Whatever changes you decide to make in this new reality can only effect that new reality. Meanwhile, the reality which you came from remains unchained. This also explains why Nebula (Karen Gillan) doesn’t cease to exist when she kills her past self from 2014; she actually killed a version of herself from a different reality.
But before you think all of this is a nice (and convenient) way of avoiding all sorts of paradoxes and time loops, this also opens a whole new paradoxical can of worms.
Marvel Studios’ AVENGERS: ENDGAME..Nebula (Karen Gillan)..Photo: Film Frame..©Marvel Studios 2019
Why the Marvel Cinematic Universe just became a multiverse
Just because the Avengers cannot change their timeline doesn’t mean their actions cannot change the timeline they’re currently in. Turns out the Infinity Stones are what anchor the universe, including time, together. Removing a stone from a certain point in time also creates branching timelines, ones which are also completely unstable.
This is what the Ancient One (Tilda Swinton) warns Hulk about when he tries taking the Time Stone from her. After all, if the Stephen Strange from the alternate 2012 doesn’t have the Time Stone, then his “Dormammu, I’ve come to bargain” plan from Doctor Strange (2016) never happens, and Dormammu wins. Hence why Hulk promises her they’ll return the stones mere moments from which they are taken to “trim the branches.”
Except, as Endgame shows, taking the stones from different realities isn’t the only thing with creates branching timelines. Thanks to the Avengers’ interference, they may have also inadvertently and irrevocably altered the futures of multiple realities regardless of whether they returned the stones or not.
The first divergence occurs in the alternate 2012 timeline. Thanks to the 2012 Hulk running into 2023 Tony Stark, Loki (Tom Hiddleston) escapes with the Tesseract and the Space Stone. Not only does this force Steve and Tony into travelling to 1970 and stealing the Tesseract again, there’s now a universe in which Loki still lives, potentially causing all sorts of mischief. It’s even possible that 2012 Loki gives Thanos the Tesseract even earlier than he did originally. Either way, everything from Avengers on in that timeline no longer happens. At least this explains how Disney Plus can develop a Loki TV streaming series when he’s technically still dead.
Things are even more convoluted when it comes to the alternate 2014 timeline. As 2014 Gamora is now stuck in 2023–where her counterpart is still dead–this means that there’s now a universe in which the Guardians of the Galaxy as we know them never formed. Moreover, because Thanos and his army at the end of the film also come from that alternate timeline, only to be snapped out of existence by Tony Stark, everything from Guardians on–including the events of Infinity War and Endgame–never happens in the alternate 2014 timeline either.
Even when Captain America returns the stones back to the moment from when they’ve been taken, he still changes those timelines. After all, those stones–particularly the 1970 Space Stone, the 2012 Mind Stone, and the 2014 Power Stone–are no longer housed in their original artifacts. Since we didn’t the Tesseract, Loki’s Specter, and the Orb respectively when Steve went back to return the stones, there’s now potentially three more divergent realities in which those artifacts no longer exist.
Marvel Studios’ AVENGERS: ENDGAME..L to R: Hawkeye/Clint Barton (Jeremy Renner), War Machine/James Rhodey (Don Cheadle), Iron Man/Tony Stark (Robert Downey Jr.), Captain America/Steve Rogers (Chris Evans), Nebula (Karen Gillan), Rocket (voiced by Bradley Cooper), Ant-Man/Scott Lang (Paul Rudd) and Black Widow/Natasha Romanoff (Scarlett Johansson)..Photo: Film Frame..©Marvel Studios 2019
Why there are still time travel paradoxes
Even if you’ve managed to grasp the concept of time travel in Avengers: Endgame, you probably still have some questions or two. For instance, you might be asking, “But if I travel back in time and the past becomes my new present, and my former present becomes my new past, how can go still back to my former present?” That’s a good question, because theoretically you shouldn’t be able to. Instead, you could only travel into the future of the new timeline you’re now in, not the one from which you originally came from.
But even if you could travel back to your own timeline, you shouldn’t also be able to travel back into a timeline you’ve previously visited and changed, either. Again, according to how time travel works in Endgame, when you travel into the past, you create a brand new timeline that diverges from yours every single time. In other words, you cannot revisit the same timeline twice. This also means Cap shouldn’t be able to return the Infinity Stones to the timelines from which they came from either.
The way Endgame gets around this, however, is two-fold. First, they have Stark’s GPS devices to navigate through the corridors of the Quantum Realm. Combined with how the time machine in 2023 acts like a tunnel, the Avengers can find their way back-and-forth across different timelines without any fuss. Presumably, this is how Cap can return the Infinity Stones to their proper timelines, even though he technically shouldn’t be able to. Also, since you still cannot return to the precise moment from which you left, Endgame shows the Avengers returning just a few seconds before they left.
That said, how did the 2014 Nebula bring her Thanos and his entire fleet into 2023? As Endgame itself establishes, you need both Pym Particles and protective environmental suits to travel through the Quantum Realm and into different timelines. Granted, 2014 Nebula gave 2014 Thanos 2023 Nebula’s Pym Particles so perhaps 2014 Ebony Maw or what have you replicated them. Also, since their ships and space whales can travel through the ravages of space, maybe they’re shielded from the Quantum Realm’s effects, too.
“But wait,” you might be asking. “Since Thanos’ ship destroyed the original time machine in 2023, doesn’t that also mean the connections to those previously visited timelines have also been severed?” Yep, which means, once again, Cap shouldn’t be able to return the Infinity Stones back to their points of origin. If you think that’s a plot hole, it’s nothing compared to the ending.
When Steve returns the Infinity Stones back to their original times, he decides to stay in the past and live a normal life of wedded bliss with his beloved Peggy Carter (Hayley Atwell). The next time we see Steve back in 2023, he’s an old man. As sweet and poignant as this ending is, it completely contradicts Endgame’s time travel rules. After all, if Cap travels to 1945, he also travels into a different timeline. Therefore, he shouldn’t have reappeared as an old man–with a fully restored shield, to boot–in 2023.
Unless, of course, Endgame‘s ending is an alternate timeline. In other words, there’s one MCU without an old Steve Rogers, and another timeline with an older Steve Rogers from the original MCU timeline–the one that we’ve seen play out over the course of twenty-two movies and elven television shows. Perhaps this was Endgame’s real twist all along.