'Avengers: Endgame' Time Travel Rules Explained

Avengers: Endgame is finally here and with the film breaking loads of box office records, countless fans are walking out of theaters having seen how the previous 21 films come together for one epic conclusion. They are also walking out with some major questions and a lot to process about Endgame including some of the major mechanics of the film's plot. As time travel is something that fans have speculated about since Avengers: Infinity War last April, that the theoretical concept gets mentioned in the film itself isn't a spoiler. But what about how it's actually addressed? Well, that needs a bit of explaining.

Don't worry, we have you covered, but before we dig into the concept of time travel in Avengers: Endgame we have to warn you: there are going to be MAJOR spoilers for Avengers: Endgame beyond this point. If you don't want to know, abandon ship now.

Alright, with that out of the way: yes, time travel plays a huge role in Endgame. The Avengers, after Thanos destroys the Infinity Stones in the present, are unable to reverse the Snap. However, when Scott Lang/Ant-Man emerges from the Quantum Realm five years later, he makes his way to the Avengers compound and reveals that time works very differently in there. That five years was five hours for him and now he's thinking that they could use the Quantum Realm to go back in time, get the stones, and undo things. Tony Stark/Iron Man is later able to make it functionally possible and the heroes set off on a mission to points of the past to get the stones.

So we know (in the film) that time travel is possible, one would think that any interference in the past would ultimately break the future. That's how it works, right? Not in Endgame. The film establishes its own rules to time travel that are actually quite a bit different than what fans might expect. While Rhodey/War Machine and Scott both have very specific ideas about time travel thanks to movies such as Back to the Future and The Terminator, the science folks are quick to explain that you can't go back in time and change the past to alter the future. In fact, that is the primary time travel rule in Endgame: for the time traveler, going into the past is the future, thus making the "future" their past. The timeline as the traveler knows it is already set. It's their reality. Anything they do in the past will not change their own reality.

With that in mind, getting the stones and undoing things doesn't wipe out the Snap, the dusting, or the past five years. It would just allow them to bring the vanished into the present. It's a little confusing, but it works from the personal perspective. But that does lead to sort of a sub-rule, if you will, about time travel and that is that if you change the past, an alternate timeline is then created from that moment. This example is most clearly explained by the Ancient One when the heroes go to the Battle of New York in 2012. Bruce -- currently Professor Hulk -- attempts to get the Time Stone and while the Ancient One understands why he needs it; she explains that removing a stone from its place in time causes a new reality to fracture off. Since there is now way of knowing how that will impact things, she doesn't want to hand over the stone.

It's a solid point, the idea of accidentally creating alternate realities and timelines, but there's a rule about that, too. To prevent that from happening -- at least in terms of the stones -- all that has to happen is the stones be replaced in time at the exact moment they're taken. Thanks to Tony's time GPS device, that's a can-do.

Together, those concepts present the three rules of time travel in Endgame: you can't mess up the current timeline by going to the past, if you do change the past you end up creating a separate timeline, but you can avoid that by restoring the stones to the point they are taken from. Sounds pretty simple, but of course things don't exactly go as planned in Endgame. Instead of the heroes getting the Space Stone in New York, Loki absconds with it and likely triggers a whole new timeline that way. Later, 2014 Thanos discovers the plan and thus changes his actions, ending up in the future (the present time of the movie) where he decides to get the stones and destroy not just half of the universe but all of it and start over. That also leads to Present Nebula killing Past Nebula, 2014 Gamora ending up in the present, and who knows what other kinds of things that, ultimately, create splintered timelines.

There's also Cap's personal decision when restoring the stones to the past that itself creates a whole new world. It's...a lot. But the upside of the complicated interactions and overly simplistic time travel rules is that the MCU as we know it remains the same. The door has just been opened for new adventures with familiar faces in new worlds going forward and that is an exciting proposition.

Avengers: Endgame is in theaters now.

What did you think about how time travel was addressed in Endgame? Let us know in the comments below.

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