Do the 'Back to the Future' time-travel rules apply to 'Avengers: Endgame'? (Spoilers!)
WARNING: This post contains MAJOR spoilers for Avengers: Endgame.
When the surviving Avengers first contemplate traveling through time in Endgame, Scott Lang begins rattling off some guidelines: Don’t talk to your future self, don’t steal a sports book and so forth. The others quickly realize that Scott’s rules are not coming from his experience in the Quantum Realm, but from the Back to the Future movies. Which begs the question: Was Ant-Man onto something? Do the rules of Back to the Future, the first time-travel blockbuster of the modern era, apply to the complex time-hopping of Avengers: Endgame? Let’s take a closer look.
In Back to the Future, anything a time traveler does in one time period has extreme ramifications in the others, butterfly effect-style. When high-school student Marty McFly inadvertently travels from 1985 to 1955 and prevents the car accident that first brought his parents together, Marty and his siblings begin to fade from existence (symbolized by his older brother and sister disappearing from a photo in his wallet, and then Marty starting to physically disappear). Marty has to convince his parents’ younger selves to fall in love to correct the timeline. Even so, when Marty returns to present-day Hill Valley, he’s in a slightly different (albeit happier) version of 1985.
This isn’t the case for the Avengers, whose trips into the past don’t have an immediate effect on the present. For example: By Back to the Future rules, when Black Widow dies in Endgame, she would also vanish from the present timeline. Therefore Natasha would never have taken over the Avengers, or traveled back in time and sacrificed herself to retrieve the Soul Stone, because she was already dead. (Yes, this is a paradox. Time-travel movies have a lot of those.) Instead, when Clint returns from Vormir, his fellow Avengers are shocked to realize that Natasha isn’t with him.
Back to the Future II adds a couple more rules to the first film’s time-travel formula. One: Bringing future information into the past — like, say, a sports almanac — can create a nightmarish alternate timeline. And two, that encountering one’s past or future self could, in mad scientist Doc Brown’s words, “create a time paradox, the results of which could cause a chain reaction that would unravel the very fabric of the space-time continuum and destroy the entire universe.”
Of course, the universe doesn’t actually get destroyed in Back to the Future II when the characters meet their alternate-timeline selves, so maybe Doc was being hyperbolic. But both these guidelines were established in that film, and they definitely don’t apply to Endgame, in which Captain America literally has a knock-down, drag-out fight with his past self. An even more extreme example: Nebula kills her own past self, which should have immediately erased both Nebulas from existence. Nebula’s case is a variation on the “grandfather paradox,” which goes like this: If you go back in time and kill your grandfather, you will never be born, and therefore you will no longer be alive to kill your grandfather. Ergo, if Nebula kills her past self, her past self will not live to become her present self, and both will disappear.
As for that sports-almanac rule, Steve breaks it during the aforementioned Cap-on-Cap fight by telling his past self that Bucky is still alive — information that should have fundamentally changed the events of The Winter Soldier were Back to the Future principles in effect. Similarly, Thor all but tells his mother, Frigga, that her death is imminent, but we are to assume that this knowledge didn’t alter the events of Thor: The Dark World.
The reason that Back to the Future rules don’t work in Endgame is that the two films have fundamentally different theories of time travel. In Back to the Future, time is a continuum, in which every action affects the entire timeline. As Doc Brown explains in Back to the Future II, any major deviation from established events will result in the creation of an alternative timeline, beginning from the moment the deviation occurred (i.e., the moment McFly nemesis Biff gives the sports almanac to his past self, thereby making his future self wealthy and powerful). The only way to fix the skewed timeline is to revisit the exact moment of the deviation, make events go the way they’re supposed to and therefore erase the alternate-universe tangent.
In the world of the Avengers, there’s no one continuous timeline with errant tangents. Instead, multiple timelines exist side by side. This concept was established in Doctor Strange and again in Infinity War, when Stephen Strange travels into the future and reports back to Tony that he’s seen 14,000,605 outcomes to the war with Thanos. This idea is consistent with the many-worlds interpretation of quantum mechanics, in which the universe is constantly splitting into parallel universes that contain every possible result of every action, even though we can only observe the specific result that happens in our own universe. In Endgame, the Ancient One explains to Bruce that the Infinity Stones are responsible for maintaining the integrity of each separate universe. Misplace the stones in one timeline, and you risk catastrophic results in that universe (and perhaps, by extension, other universes? The Ancient One’s floating-light diagram doesn’t make this entirely clear).
The multiverse idea is a mainstay in Marvel comics, which is why Spider-Man can be Peter Parker in one series and Peter Porker, Spider-Ham in another (as Spider-Man: Into the Spiderverse illustrated quite brilliantly). But Endgame plays fast and loose with the rules. Take Steve, who returns to the past to live out his life with Peggy Carter. That is most assuredly an alternate reality, since Steve grows old in entirely different circumstances than the ones we’ve seen. Yet at the end of the film, he returns to the main timeline through Tony’s machine, as if he were there all along.
Also in Endgame, Gamora from the past travels into the present. The present-day Gamora was killed by Thanos so that he could obtain the Soul Stone. That means that the only Gamora who exists in the present time is Gamora from an alternate timeline… right?
Endgame’s explanation for all its inconsistencies is that the Infinity Stones generate a kind of selective reset function, undoing the Snapture while keeping other events in place, and not affecting the larger timeline as long as the stones are returned to the exact moment in the past that they were stolen. Just don’t think about it too hard. The time-travel device in this film is not designed for logic, but for maximum storytelling effect. And of the many ways the final Avengers film could have gone, this one seems like the best of all possible worlds.
Read more from Yahoo Entertainment:
'Avengers: Endgame' ending explained: Who died, who survived and what comes next (SPOILERS)
Why 'Avengers: Endgame' does the end credits differently (spoiler-free!)
'You get chills': Chris Evans reflects on 8 years of playing Captain America, wrapping 'Endgame'
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