I like the persistent present. We simply live with the paradoxes.

“Remember when Hitler was assassinated in 1919, 1933, 1936, and 1939, then off’d himself in his bunker in '45?”

Something else entirely, I don’t think we’re capable of understanding time (yet?)

The first one makes the most sense to me, which is why I think time travel should be used to make significant changes. Go big or go home

Paradoxes slowly disintegrate the timeline you’re in. Thousands of years, Deadpool 3 rules.

You can only change things you don’t know about in advance. You know Hitler became chancellor of Germany, so you can’t change that. But you can change the name of his dogs if you don’t know what they were, and nobody who knew sent you back in time.

The most interesting one to me, and the one that makes the most sense, is that changes propagate forward in time at the same speed as everything else, so 1 second per second. Why would causality suddenly decide to go any faster than that? This effectively means that all “alternate timelines” exist on the same timeline, and overwrite each other as they move forward.

You can visualize this by coloring the original timeline red. When you time travel backwards, you arrive at an earlier point on the timeline and it begin overwriting it orange, with the “head” of the orange section expanding into its future, which is previously red. If someone travels into the orange area again, it turns yellow, etc. If the instant where you time travelled backwards to make the orange region gets overwritten, the color of the timeline to the left of the orange region would begin expanding to overwrite it at the same speed as any other change.

This does lead to some interesting things, like two time travel loops that include the same point in time literally slowly corrupting the timeline. One loop, where you travel back, wait until when you left, then travel back again, would cause the future from your departure point to continually be overwritten by each new loop color, sending constant-width “bands” of colored time forward before they’re overwritten by the band from the next loop. Two loops’ bands would almost certainly not be commonly divisible, so you’d eventually end up with “bands” moving forward and within the loop that get smaller and smaller, fragmenting the timeline into colored noise. If you lived on the timeline, though, you wouldn’t notice-- even if you’re in a timeline band that’s only 1 second wide, you move with it, so nothing seems out of the ordinary. But if you travelled back to the same point in time repeatedly to check on it, or could freeze yourself in time and watch the bands pass through your point in time, things would be changing incredibly quickly. This also means that waiting time in the future before travelling backwards in time would let the past have time to be overwritten by a different band, so the same point in time would be different depending on when you left the future. All timeline damage would be repaired (at band-expansion speed) if you could remove all instances of time travel backwards to the offending loops, though.

IRL, the speed of causality depends on your speed, too, and in theory, timeline changes would expand outward at the speed of light. My brain is not big enough to think through all the potential consequences of relativistic weirdness and time travel at once, though. I suspect it would allow for “bands”/fragmentation not only in time but in space as well.

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.

• You branch off into another timeline and your actions make no difference to the previous timeline

New actions, new consequences.

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.

• something else

3 dimensions of space + 2 dimensions of time

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.

Its a one way trip. You can never go back to the original universe.

My personal favorite?

Space and time is an infinite number of parallel realities that constantly compress and unravel at every possible random chance. We are 4th (or 3.5th) dimensional beings that experience the most probable result aggregated from an infinite existence. If you time travel back in time, and change the past, it would not affect the your past, but it would affect your future, if you time traveled back to your current time.