How time travel works in Marvel’s ‘Avengers: Endgame’

Warning: MAJOR spoilers for Avengers: Endgame below.

Time travel can save the fate of the Marvel Cinematic Universe, and make your brain throb worse than a hammer to the head all at the same time!

Leading up to the epic release of Avengers: Endgame, plenty of folks (yours truly included) were worried that the inevitable addition of time travel to the MCU would undermine the series’ fundamental structure and leave our favorite heroes in a pile of mind-numbing paradoxes, fallacies, and plot holes.

Lucky for us, Endgame managed to slay the time-travel behemoth. Or, at least, hide it — and its many confusing inconsistencies — out of sight. 

If you’ve just gotten out of your Endgame showing and are scratching your head trying to put together the pieces of what you saw, I’ve got great news: There is no answer!

Really. Put down the paper and pen, bail out of your calculator app, and save yourself the multi-day headache of sorting through this mess. There is no easy explanation as to how time travel works in Endgame — and the people who created it have to have known as much.  

Want to try and wrap your mind around it anyway? Great! We’ll try and muddle our way through it together.

Endgame‘s basic time-travel philosophy

The question with Endgame (and pretty much all time travel films) isn’t so much how it’s possible characters can time travel, but what it means for the state of reality when they do. 

In most time travel films, including many of the films jokingly identified by name in Endgame, events changed in the past dramatically alter the future. 

Take War Machine’s “Kill baby Thanos” suggestion. In a standard time-travel setup, this would totally work in terms of preventing the many horrible things that come with Thanos’ rise to power. If Thanos is never born, then The Snap can never happen. 

Of course, that “solution” comes with an infinite number of complications à la the butterfly effect. Addressing these often undesired outcomes is the meat of most time-travel films.

These complications don’t exist in the MCU, however — at least not according to the Hulk. At one point, he explains, “If you travel to the past, that past becomes your future and your former present becomes the past which can’t now be changed by your new future.” 

Put more simply: When characters travel to the past in Endgame and remove Infinity Stones from various timelines, those timelines then create branching alternate timelines rather than changing the “original” future. When those same characters return to what they would consider the present, they arrive at their own timelines, and not the ones they’ve just created by removing the Stones.

So, for instance, going back and killing infant Thanos would create a timeline without him and his crimes, but the Avengers we know and love would not be in that specific timeline.

Returning the Infinity Stones 

If we’re just focused on “our” Avengers from 2023, then stealing the Infinity Stones and rectifying the main storyline is all gravy. They bring the Stones back to the present, do a quick snap to get everyone back, and break early for some shawarma — the Nebula complication not withstanding.

Except there are the egregious moral implications of jacking up the lives of everyone in all those other timelines and just peacing out.

Enter Tilda Swinton and her handy-dandy magic diagram. As the Ancient One explains to the Hulk, those alternate timelines rely on the presence of the Infinity Stones to save themselves from certain peril. That’s why 2012 Tilda is so defensive of the Time Stone in the first place — without it, Doctor Strange can’t beat Dormammu and Kaecilius in 2016 and that timeline is doomed regardless of the Snap.

The Hulk promises to return the Stones to the points in time where the Avengers first got them, so all of the timelines can once again be in alignment. That would put a neat little bow on this time-travel tale, except … 

The Steve Rogers(s) problem

The guy who ultimately volunteers to return the Stones to their timelines is our ol’ pal Captain America, who, as revealed by that incredible ending scene, returns the Stones, but then stays in the past to be with Peggy Carter. 

If we choose to believe that’s all one timeline, then that means for all 22 films of the Infinity Saga there have always been two Steves. Presumably, older Steve avoided younger Steve to prevent any weirdness and lived out his (their?) new life happily ever after. 

But there’s a wrinkle: In Captain America: The Winter Soldier, we learn that Peggy got married and had kids while Steve was in the ice. So did Peggy just hide Steve from her husband in a closet the whole time? But then that makes their conversation in Winter Soldier really strange? And Peggy kind of a sociopathic monster? And Steve a little kinky? 

Or since Peggy doesn’t specifically name her husband when she talks about him in Winter Soldier, was she just talking about older Steve the whole time? It all gets very complicated.

Alternatively, if we assume Steve lived out his life with Peggy in an alternate timeline (one where she never married the other guy), how in Asgard’s name did he get onto that bench? He is in another reality/timeline/universe, and that bench is in the one he left. 

The entire time-travel philosophy of Endgame prevents Steve from getting back to that original timeline via normal aging, because by changing his past, he split his timeline into a branch that goes away from his 2023 life. 

Once again, “If you travel to the past, that past becomes your future and your former present becomes the past which can’t now be changed by your new future.” (!!!)

Hypothetically, Steve could have built a machine to channel The Quantum Realm so that he could specifically return to the 2023 timeline on the day of Tony’s funeral for that “Gotcha!” moment. But honestly, we doubt it. That’s a lot of effort for a single dramatic pronouncement, and Cap isn’t exactly the quantum physicist in the room. 

The Loki problem

And then there’s that whole Battle of New York 2: Electric Boogaloo mishap, where Loki vanishes with the Tesseract in tow. As best we can tell, everyone in that timeline was left in deep, deep shit.

There’s no clear explanation as to what happens for the inhabitants of a universe in which Loki has total control of the Space Stone. For starters, it makes Thanos acquiring the other Infinity Stones of that timeline a whole lot easier. That could play out in a variety of really problematic ways if the 2023 Avengers don’t intervene, but where would they even begin?

They could (hypothetically speaking) head back to Stark Tower in 2012 again, and have Captain America fix that mess while he’s there. But there’s nothing in Endgame to indicate they have any plans of doing that. Simply put, there’s an MCU in which 2012 Loki won. 

The Gamora problem

Finally, there’s whatever is going on with Gamora. 

As best we know, 2018 Gamora, sacrificed by Thanos for the Soul Stone, is 100% irreversibly dead. However, we saw 2014 Gamora time-travel with 2014 Thanos and 2023 Nebula to the 2023 Battle of the Earth and have that whole back-and-forth with Star-Lord. 

Later, we saw Star-Lord looking into Gamora’s whereabouts on the Guardians’ ship, indicating that he has some sort of plan for getting her back.

We can’t yet say that this is a definitive problem in the Endgame time-travel scheme, but once Guardians of the Galaxy Vol. 3 premieres in 2020 — which Zoe Saldana is totally going to be in, by the way — we’ll likely have some (very universe breaking) answers. 

Is quantum mechanics the answer?

If you’re a specialist in quantum mechanics, the confusion surrounding Gamora, the problematic possibilities with Loki and the Tesseract, and the double Steves, may be easy to explain away using specialized knowledge of quantum mechanics. 

This advanced field of physics is clearly where Endgame creators and characters have based their understanding of time-travel, as the characters mention it frequently. And it may hold the mathematic solutions needed for patching these apparent plot holes. 

But when your blockbuster movie requires audience members invest in a doctorate, that’s probably a problem.

Out of sight, out of mind (stone)

All the being said, Endgame is still an unmatched finale for a historic franchise. In the words of Mashable’s Angie Han, “Who’s stressing about the logistics of this twist or that one, when everyone around you is screaming with joy over the big reveal?”

Take a deep breath, let the specifics go, and trust Marvel nailed the time-travel plot… just in a different universe.