Stories involving 2 are often the most fun, as well as 4 if they aren't lazy with the timeline corrections

1 feels the simplest and I would prefer it. With 3, unless the technology is limited to a few people, it's going to get messy

Either 1 or 3. I tend to lean towards 3

I mean I would say causality would be followed. So you change things and essentially create a new timeline. The only thing with that is if your time travel system could handle it. If you go back will you go back to your old timeline or your new one? Maybe you could choose but not necessarily. and of course any time you return to a point before you left you are further creating a new timeline. You would have to return after you left to preserve whatever you return to. So basically causality follows the individual and timelines pretty much always get created when time travel happens. Another interesting possibility is if you can manage to not change anything at all maybe you could stay in the original timeline. Its hard to say if that could even happen though as it would need at some point an original timeline without time travel to work off of.

I think it would be like the first one, except instead of you going back to that time, you would be making a copy of that time to traverse to from your time, similar to how moving a file between devices causes it to be copied.

A relevant quote from a physicist is "some will say it's easier to predict the future than the past, since a single effect can have multiple possible causes but a single cause can only have one possible effect."

Whichever is closest to science and physics.

It'd be a horrifying thought if the time travel theory you believed in was different to what you got, UGH just the thought gives me existential dread.

This also reminds me of:

• something else

3 dimensions of space + 2 dimensions of time

Probably "read only"/neighboring dimensions. Can't change the timeline you came from. If you could there's just no way there wouldn't be evidence of people doing it.

But otherwise I guess "all changes due to time travel have already happened" as incompatible with free will as it is.

One timeline, actions can have an effect. But once you time travel you unmoor yourself from normal causality, so you could do things that should negate your existence and nothing will happen to you.

Indeed, if you time travel again you can't affect your own actions anymore. Like, you travel back 20 minutes, do things for an hour, then jump back 5 minutes, when you go back the second time you can't alter yourself. You could go later the you from before you ever time traveled though.

Each has Pros and Cons.

I liked what the show Dark did with the first idea. Having a constant move of time, and a fixed "jump distance"is really cool. Each new timelone also has those points, but some just happen to be created or destroyed in your lifetime.

The second seems kinda boring in real life (except for visiting the past) and can get really tricky fast if it would be usable in real life, but in movies it mostly rocks.

Having actions matter is very cool, but sounds dangerous and paradox-y. If not done like in Looper its still fun though (for real, don't watch that movie) and maybe it even has a fixed flow of time (like the tomorrow war).

What I would want the most and what prevents a lot of paradoxes though is the trope of "getting sent back into your younger body" like in butterfly effect (which got real stupid in the second half with the Jesus hands). But I would still really like that and in the best case with the possibility of going back in time after my death.

1

I think technically idea 2 and 3 have the same end result. I can't see 3 working without 2 already being true.

I'm definitely subscribing to the 3rd one, even if the 2nd one makes more sense to me...

Causality fracturing. Partly because observing Mandala effects. Basically causality has inertia and plasticity like matter, so soft changes bend and big changes tear, and inertial mass is also proportional to the time between the incursion and excursion points.

The first one. Specifically because of wave function collapse (ie. The cat is both alive and dead until the box interacts with the universe)

I either could have or could not have travelled back in time to the year 1927. In our present universe, the wave function collapsed and revealed that I didn't. If I went back in time to 1927, I'd essentially be re-rolling the dice, causing the wave function to collapse again, this time revealing that I did in fact move back in time.

Re-rolling the dice doesn't change the initial roll. It's immutable in the fabric of reality. All I'm doing is creating a new universe in which I did travel back in time.

If I were to then move forward again, I'd be in the new timeline, not the original one. There's no going home again. Which is why Sam Beckett was never able to return home. He spent four seasons creating different universes where one person's life was better at the expense of a bunch of others.