All right! So you have 4 types of time travel. They break down like this:
Causal linear – Stuff in the past directly affects stuff in the future. If I kill a dude in the past, he is dead, his kids never happened, etc.
Non-Causal linear – What you do in the past will not affect the future. That time self-heals and corrects for mistakes.
Causal non-linear – Stuff done in the past creates a split-off universe. Go back and kill someone and his kids are fine in YOUR FUTURE AS THEY ALREADY WERE, but you create a second universe where they never happened. Which one you go back to is down to story mechanics, etc.
Non-causal non-linear – Stuff we do in the past affects the future but also leaves the future alone. It is a paradox method of travel.
SO! Back to the Future 1 uses causal linear, right? Marty doesn’t get parents to meet – he won’t exist (we will ignore the problem that such changes should be instantaneous and yet seem to take different amounts of time to happen, meaning, theoretically, that the changes themselves have to travel in time back to the future to effect it which… is a different problem).
But in BttF 2 they make a change and end up in a split off time stream. That’s Causal non-linear! So they use both and fuck it.
Terminator, of course, uses only the basic causal linear model. It is the simplest.
Looper gets crafty. It starts by showing us, through the punishment for not closing a loop, that it is Causal linear. Simple enough. But then it creates a paradox. We see Bruce Willis come back twice, with two different results. Results that stay with the same time line. So the rest of the movie is in paradox already.
And we go along. And at the end Gordon-Levitt kills himself. Bringing us back to Causal linear. But that paradox can’t be causal linear because the system wouldn’t allow for it. So it must be Non-causal non-linear because that allows for the following:
What you do in the past will change the future. But the future that happened also did happen, up until the change. At which point it both did and did not happen. It is a paradox Universe. And that’s ok. Because in reality, it is probably the closest to what actually happens.
This, for the record, is also how Doctor Who works.
Because the universe is NOT just 1s and 0s floating in space. Sorry. It is also what we observe. Heisenberg opened that door and he’s right. So did Schrodinger. See… once you can tell where an electron is but not how fast it is going (or vice versa) on an atomic level you are literally saying “Until I saw both and labelled them – all of it happened” it didn’t retroactively go into a slot. It was in them all until them. This is, in fact, why electron clouds work.
Schrodinger, of course, brought us a cat whose state is unknown until observed. Once observed though, it collapses the probability wave. It if was A/B before you looked and A after – that does NOT mean it was A before you looked. It was, in fact A/B before you looked. That’s fact.
We live in a paradox universe.
If I go back and kill your grandfather, and I wouldn’t I hear he’s a great guy, upstanding citizen, He would die. You would vanish. But the things you touched and affected in your life would still have happened – up until the simultaneous and yet not-at-all-linear second I killed him, and wiped you out. At which point you didn’t exist. Except you totally did. Crushed a flower when you were ten – that flower was still crushed. By you. Except it wasn’t.
And the universe spins on. Because a basic fundamental paradox is built into the way the universe works and it is 100% fine with it.
We simply never developed grammar for a did/didn’t situation. And we need to. Because it is how the universe works, and we can’t explain it right without things getting messy. But. Using the tools we have:
We live in a non-causal non-linear universe. Looper was just being honest about it.