Time travel is a common element in movies. You don’t need to be an astrophysicist to appreciate, “what if?” Time travel can be added to a plot fairly easily, but the explanation behind its design, or the technicalities upon which it’s explained, is where things can get dicey.
Whether or not the entertainment industry is aware that they’re designing time travel in one of two ways is a mystery, but they are being presented as either a closed loop, or an open system. Keep in mind, these are not technical terms. They are what I use to help the entertainment industry stay organized in what would otherwise be a very complicated math problem.
A closed loop is one universe, one world. If you go back in time, then you’re going to do exactly what you were always going to do because you already did it. Even if you try to change the past, the same outcome will occur because you were always going to do that thing. That is how Arrival worked, Interstellar, Harry Potter, and especially Tenet.
Even knowing what’s going to happen, and being given a “choice” to change the outcome ends with the same results. The characters end up right back where they started. It is one universe, and it is destiny. You’ve already made the decision. You just don’t know what it is yet.
The closed loop is the journey to figure out why the character did what they did.
An open system is the multiverse, parallel universes, etc. If you go back in time and change the past, you’re in a new universe now. Whether you created it or not doesn’t need to matter, but you are no longer in the universe you came from.
That is most of the Marvel Universe, Edge of Tomorrow, Star Trek and at the end of Back to the Future where his dad is super successful and he’s living in a big house now. Different universes, different outcomes. In the open system, you can change what happens in other universes, BUT if you return to your old universe – the one you came from – it’s still exactly the way you left it. Nothing changed there.
I’ve noticed that dramas and the more serious thought-provoking movies tend to incorporate closed loops, while action and sci-fi tends to be open. Probably because sci-fi and action are more of a thriller and allow crazier stuff to happen, while a closed loop is more of a psychological journey on why things turned out the way they did.
There are a lot of reasons why you can’t change your own universe and instead have to go to another one, but the simplest is that you can’t create or poof matter out of existence. You can’t replace your entire universe and all of its matter and energy and data without first destroying what’s there. And that would require more energy than the universe has.
It makes no sense.
If someone has changed something in our universe, like a hundred years ago, we would have no idea. Maybe it’s already happened. Maybe that’s what the Big Bang is: a more advanced human species starting and restarting the universe to yield different results.
Have you tried turning it off and turning it back on again?