The Rules of Time Travel in Avengers: Endgame

Ok, standard disclaimer first, this whole post is one big spoiler, so reader beware..

Second thing, I am not here to tell you how time travel actually works in the movie. And I am most certainly not here to tell you if the way it works in the movie could theoretically work in real life. Both these endeavors would take about 3,000 units of raw intelligence, and last I checked, I only have about 144.

I am only here to tell you what the rules of time travel are in this film, apparently. I listed these rules just to see if there is a set of rules under which every scene in movie would come together in a consistent, non-contradictory way, and viewed through the prism of these rules, I think the movie makers came pretty close. Kudos to them.

Rule #1: What's done is done. Traveling back in your reality changes nothing about what has already happened in your reality. Making changes in the past, like retrieving the infinity stones, creates an alternate reality (and thus a multiverse) but changes nothing that has already happened in yours. This is why the Avengers couldn't just go back and kill a young Thanos, an option which War Machine wondered about.. Doing so would have just bought them to an unpredictable alternate reality which, for all they knew, might have turned out to be worse than the current one. They wanted their current reality, but to bring back that half of the universe that Thanos had snapped into oblivion.  Rule #1 also explains something I spent quite a bit of time wondering about - why they needed to make a gauntlet and have the Hulk snap it. If all the stones were retrieved long before the year 2018, I wondered at first, how could the events of Infinity War have taken place? No stones, then no glove, then nothing for Thanos to snap, and half the universe never turned to dust. But apparently, the rule is, what has already happened cannot be changed, even if you go further back. When the Hulk snapped the new gauntlet, he wasn't changing the past, he was executing a new action that reverses the effect of a past action. It's like a computer file accidentally deleted. You cannot change the fact that the deletion happened, but you can go to the recycle bin and undelete it. To emphasize, this doesn't mean that one's actions when time traveling in the Marvel Cinematic Universe have no consequences, but rather than changing what has already taken place, they create alternative branches of reality. The Ancient One (aka bald lady) explained this quite clearly, after which Bruce Banner swore to return the stones in order to restore a universe with a single reality.

wired.co.uk

Rule #2: The time traveler can co-exist with his/her non-time-traveling self at any given place and time.  This is actually pretty clear and best illustrated by Nebula. She clearly came face to face with her old self and even killed her old self. Many of the Avengers also saw themselves, and Captain America even fought himself. If you're wondering how killing your old self doesn't also make you dead, refer to rule #1, nothing you do in the past changes what has already happened, and Nebula has already lived up to 2019. Killing her old self doesn't change that. The most interesting application of rule #2 is in the case of an old Captain America at the end of the film. Yes it was meant to be a sweet moment showing how even a superhero can make choices in life in the name of love, but initially it does lead to some logical discomfort, because if Captain America was old by 2019, who was that fighting just a few days ago in that final climactic battle between good and evil? He was even wielding Thor's smaller hammer for crying out loud. But our rules come to the rescue in a pretty neat and elegant way: after the final battle Captain America volunteers to go back to the past to return each of the five stones, after which he decides to stay in the 1940s where he made a different choice not to be a superhero but to be with Margaret Carter instead, and from thereon he quietly co-existed with his Superhero self, right up until his Superhero self went back in time to return the stones, and then there was one Steve Rogers again, the old, non-superhero one. So actually, for a few hours in New York in 2012, there were three of them co-existing. 😃 Yes, this is just my theory, but give me a better explanation of how an old Steve Rogers turned up on a bench at the end of Endgame and I will gladly take it back.

bustle.com

Rule #3: You can't change the past, but you can bring something from the past into the future. This doesn't need much analytical proof because there are very clear instances of this. Thanos had already destroyed the infinity stones, but while the Avengers could no longer change this, they could still have stones now by going into the past and bringing the stones into the future (the now). Gamora was also another very clear example, Thanos had thrown Gamora off a cliff to her death as a condition to gaining possession of the Soul Stone even before Endgame, but she was at the final battle because Thanos bought her from the past into the future. To keep with our deleted file analogy, although we can't change the fact that the deletion took place, we can still find, and use, an earlier copy of the file we might have saved somewhere.

Rule #3 is incredibly HUGE. Because it provides a loophole through which the Marvel Cinematic Universe can bring people back from the dead. Really. Think about it, eventually someone will realize that while they can't change the fact that say, Black Widow died, (Hulk said he tried with the gauntlet, but couldn't), what they can do is to time travel to a point in time where she was alive, and bring her to the future. If you think I'm crazy, well, I have one word for you: Gamora. 😀 This bodes very well for the viability of the Marvel Cinematic Universe, and of course, its profitability. 😋

My Nitpicks: While the exercise of articulating these three rules does enable me to find a consistent logical basis for the entire Endgame story line, I do also have some nitpicks:

1. I feel the most logical place for the Avengers to time travel to should have been that garden planet where Thanos retreated to following his snap in Infinity War. As long as they went within the first two days, all five stones would've been there. Seems to me it would have been the most efficient time and place, but I guess it wouldn't have been much of a movie then.  I might be missing something, but I can't think of a single reason why they didn't go to that garden planet in those two days.

2. The film was quite clear that five years had passed in real time between the demise of half the universe and the events of Endgame, but by the end of the film Peter Parker is shown going back to school without seeming to miss a beat. Shouldn't his peers be five years older than him by now? Unless they also turned to dust too and came back. But... all of them? 😐

3. I seem to remember quite vividly that in Infinity War, Vision had already sacrificed himself by having his girlfriend Scarlet Witch destroy the mind stone lodged in his head, but Thanos used the time stone in the yet to be fully functional gauntlet to change the past, revive Vision with the stone still whole, before taking it from his head, and killing him. So, doesn't this show that the stones do have the power to change the past? Time travel can't., but the gauntlet can. So while the Avengers would still need to time travel in order to get whole stones, it seemed they could have done a whole lot more with the gauntlet once they had it in their possession.

In the final analysis though, what I've realized is that these MCU movies are entertainment and  I really ought to watch them as if I'm reading a comic. I must admit that for some reason, watching a live action film makes me instinctively hold them up to a higher standard of realism, which really ought not be the case. No one could be as smart and cool as Tony Stark right? Billionaire, playboy,  genius, philanthropist.