There are two moments that telegraph this idea. In one scene, the younger and older versions of Joe sit at a café, seeing each other for the first time. Young Joe starts to ask the questions that audiences ask of every time travel story, and we brace ourselves for head-splitting paradoxes. Instead, old Joe dismisses the whole premise they are experiencing with a swipe of his hand.
“I don't want to talk about time travel because if we start talking about it then we're going to be here all day talking about it, making diagrams with straws.”
Earlier in the film, right after old Joe appears, there is a sequence that we see—but actually never occurs. In it, we see old Joe show up and get killed. Young Joe then proceeds to live out his life until the moment when he is old and about to be sent back to die. He then makes the choice and takes an action that causes everything we just saw to never occur. It starts out so jarringly, we are a bit confused—but by the end we have had to make a choice ourselves. Are we going to ignore the impossibilities and let the movie do its thing, or not?
If we go with it, we get a couple rewards. First we get the classic idea of an older, wiser man having the chance to talk to his reckless, stupid, younger self. Instead of trying to give himself advice, he is determined to change circumstances that will ruin his future life. He knows that there is no talking to his former self. That is not the way to effect change. A flaw of fools is that they don’t listen.
So, instead we get the most asked of time travel speculations. “If you could go back to when Hitler was a kid, would you kill him to save millions?” This is what old Joe, in his version of reality, is out to do. He wants to eradicate an evil from his world before it has a chance to become. The brilliant thing that Rian Johnson does here is to conduct the circumstances of his story to bring Joe (and us) to the unavoidable conclusion.
“Then I saw it: I saw a mom who would die for her son; a man who would kill for his wife; a boy, angry and alone laid out in front of the bad path. I saw it and the path was a circle, round and round. So I changed it.” -young Joe in voice-over
Without completely giving away the details of Joe’s solution, it is a great job of showing us that Hitler wasn’t the sole problem. We all are. We humans have a tremendous capacity for evil. The only person we have a chance to control in any sort of way that could improve things is ourselves, and ultimately we are helpless on our own to do the right thing. If there is any person who could be “taken out” to improve things it would be us, and even that doesn’t solve the problem of all the other bad people walking around out there.
This film does a creative job of exposing the problem, but that’s as far as it goes.