Some ideas are:
- You branch off into another timeline and your actions make no difference to the previous timeline
- You’ve already taken said actions but just didn’t know about it so nothing changes
- Actions taken can have an effect (so you could suddenly erase yourself if you killed your parents)
- Only “nexus” or fixed events really matter, the timeline will sort itself out for minor changes
- something else entirely
- something else
3 dimensions of space + 2 dimensions of time
Yes. If you go back in time, you end up where the Earth used to be at that moment, I.e. thousands, hundreds of thousands, millions, hudreds of millions kms away. Arguably, if you go back a full galactic year you can end up somewhat in the vincinity of the solar system.
Time travel wouldn’t be by jumps but by contionous change in perpendicular* time dimension.
So earth wouldn’t escape from your feet as you would move with it, just like you are doing right now with just one dimension.
*time travel would be imposible if you can move only in one direction. ~~Then the 2nd time dimension would need to be under some funky angle (3/4π>α>1/2π and α≠π and α≠0) ~~ i am wrong
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
- You branch off into another timeline and your actions make no difference to the previous timeline
New actions, new consequences.
This. Time traveling is a purely selfish endeavour.
Go back and kill Hitler? Congratulations! Only you understand what changed. Doesn’t help the 7 billion people you left in your original timeline.
But you now get to live in a cool alternate reality where the soviet union clashed directly with the allied forces as the axis never existed.
. . .
Kirov reporting.
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.
The reason time depends on speed is because you are always moving at the speed of light, but the vast majority of that is going in the 4th dimension: time. If you speed up in a given direction you’re losing speed through time to make up for it.
I always found that idea so cool for some reason
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.
What if you tried to change his dog’s name to something very unlikely? Like, I’m really pretty sure Hitler’s dog wasn’t named Bark Obama, but I really cannot be 100% sure.
If the fact that President Obama didn’t share a name with one of Hitler’s dogs was historically impactful enough to shape your decision to go back in time and change the dog’s name, then you can’t do it.
If there’s a possible way that the dog could have had that name and you wouldn’t have been aware of it (like if the media never connected the dots), then it’s possible.
The one where you can only jump forward, not backward. It avoids the common paradoxes.
we already live in that one
See? Problem solved.
Either 1 or 3. I tend to lean towards 3
You’ve already taken said actions but just didn’t know about it so nothing changes
12 Monkeys did this one perfectly.
You can’t change things because if you undid the thing, then there wouldn’t be a reason to undo the thing. If you go back in time, you are just going to do what you already did because that is in the past.
I’d totally forgotten about 12 monkeys. I had that VHS of this when I was 11 or 12 years old, I probably watched it 30 times and I never fully understood it. 25 years later I think it’s time for me to rewatch this
Rewatched it recently, it held up really well!
If you go back in time, you are just going to do what you already did because that is in the past.
Only if the Universe is deterministic. If not, random rolls having different outcomes may completely change the course of events and decisions made by people.
Maybe this is the same as what you’re saying but my issue with the idea that “You’ve already taken said actions but just didn’t know about it so nothing changes” is that it means time travelers don’t have any free will once they go back in time. If that’s the case, then it bring up existential concerns and that might extend to non backwards time travelers (i.e. us)
I think from a physics standpoint, strict free will is already an illusion and the only useful definitions of free will basically boil down to “choices can be made”, perhaps as far as “Slight differences in initial conditions can lead to different choices” (but somehow excluding random processes). That kind of definition doesn’t even require consciousness, and is compatible with a deterministic universe like ours seems mostly to be. Would also be compatible with the time traveler unwittingly doing everything as must happen, but still via individual choices.
Are you saying that even without time travel, free will is an illusion? Surely there has to be a time travel scenario, like going back 1 second in time and shaking hands, where all information is known to both travelers, and the future self would know what was done previously, and can choose to take a different action.
Choice is one of the slight differences that can lead to different outcomes. A rock falling down a hill will always fall downhill because of gravity. An animal can choose to slow itself or even work against gravity to move uphill. Instead of gravity, there are a ton of prior experiences that will influence that choice, but choice is still a distinct part of the process.
Exactly. That’s why I think the only useful definitions of free will are those that are weak enough to distinguish between the animal and the rock in a situation like that.
You’re assuming that time travel is equivalent to “rewinding” the intervening time span as if it had never occurred—in which case, yes, nondeterministic events are likely to happen differently.
But that’s not the case if time travel is a closed time-like loop (which is implicit in the “immutable-past” scenario in OP’s point 2). In that case everything happens only once, so it makes no difference whether or not the universe is strictly deterministic.
Nothing is truly random, including the weather. It is extremely complex and difficult to predict, but once it happens that is what happened. As long as dice fall with the exact same speed and hit the same surface in the same spot at the same angle it will always end up with the same result. The randomness of dice comes from how the very small differences influence the outcome.
Going back in time with the knowledge of what happened the first time means that either you will choose the same thing because something led to that original choice or something will keep you from interfering. Free will exists because we don’t literally know the exact outcome of our actions or the things outside of our control in advance.
Nothing is truly random
Modern physics says otherwise. Einstein also thought exactly like that with his “hidden variables” theory which was later disproven.
Edit: I was interested to read some relevant discussions and here’s some links with quotes
https://philosophy.stackexchange.com/questions/29364/does-true-randomness-actually-exist
It seems very likely that every deviation from perfect homogeneity and isotropy in the universe is due to amplified quantum fluctuations. (That’s true in inflationary cosmology, and I’d expect it to be true in practically any alternative to it.) For example, the shape of Earth’s land masses was probably determined by quantum fluctuations, and has had an enormous influence on human history.
Quantum fluctuations is basically true randomness on quantum level.
The randomness is largely canceled out, except in the case of unstable systems which magnify the effects of any perturbations, no matter how small.
Oh, I’ll have to watch that
Logically speaking it’s the only way time travel can be done, and for bonus points physics wouldn’t have a problem with it.
Any Back to the Future shenanigans is just creating alternate realities, which may or may not instantly destroy the original.
"Default behaviors is undo, no redo. You control undo the undo. Emacs.
I recommend undotree, which is also a non-destructive undo, but for some cases makes it easier to reach those points.
Probably the branch off one.
Though, speaking of time travel, I really don’t understand/like the whole Harry Potter dementor (however it’s spelt) lake scene in the movie where future Harry saves past Harry. How does that work? Wouldn’t in an initial timeline Harry have to somehow save himself before he could travel back in time to save his past self? The way I see it, it just looks like an infinite cycle of Harry saving his past self with no origin point.
Probably something like attractor field theory from Steins;Gate. In my view it’s basically timelines with a bit of topological though thrown on it to combine closely related timelines into bundles, similar to some algebraic topology concepts I guess.
From a narrative sense the “nexus” theory is certainly the most amusing, which is probably why Terry Pratchett posited it works exactly that way on numerous occasions. It turns out that history really is kings and battles and speeches and dates, and in order for history to have actually happened someone has to observe those critical events. The things in between really don’t matter. History as a whole further finds a way of happening whether people are involved in it or not, and regardless of – or possibly despite – anyone attempting to hinder, help, or change it. The key events will always happen eventually. All anyone can do is slightly influence how long it takes for them to do so, which is why there are so many boring spans in history where it seemed like nothing really happened; That’s because it didn’t. Possibly until some history monk noticed, and came along to pull out whatever spanner was holding up the works.
If it actually existed, then obviously I would subscribe to whatever theory most accurately described how it worked. That’s science.
If you’re asking which theory I would predict is most likely, knowing only that time travel was possible as a starting point, then there are only two that I’m aware of that are logically consistent. Either:
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Single fixed timeline, whereby if you go back in time then whatever you do there was already a part of history from the start. You won’t be able to “change” anything because you were always there. This is the approach described by the Novikov self-consistency principle.
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Multiple worlds, in which if you go back in time you just end up following a different “branch” of history forward from there.
Any of the models that let you “change your own history” are logically inconsistent and therefore utterly impossible. They just can’t exist, like a square triangle or 1=2. They may be fine for entertaining movie plots but don’t take them seriously.
I just imagine if life is a simulation and everytime someone travel back a new branch created but then coming back to present timeline you have to fix all the merge conflicts.
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Are you asking which system I think is the most plausible, or which is the most desirable?
Plausibility:
Well, I’d guess that time travel probably isn’t possible, and if it is, it’s probably under extremely limited conditions that render it impractical for viable exploitation. But if you’re operating under the assumption that it is, I’d say the “your actions do not affect this timeline” or similar type.
Why?
We have had no record of time travel or seen phenomena likely resulting from it. If at time T, time travel is discovered, it seems unlikely that someone after that time wouldn’t have come back in time and done something that we’d have noticed.
And it’s not just us. If self-timeline-affecting time travel is possible, then you consider all the possible civilizations out there in the universe who might discover it at some point in time and want to take advantage of it. Yet we’ve seen nothing from them. It’s the Fermi Paradox on steroids. The Fermi Paradox asks why intelligent aliens, half of whom statistically probably evolved before us and should have colonized the universe if they’re out there, aren’t visible to us. The time to travel over even huge distances, though it is large, is small compared to the time required to evolve a spacefaring civilization. But in the presence of self-timeline-affecting time travel, then even the evolutionary time becomes a non-factor, since civilizations from the future could also show up, and roll back in time with their advanced technology and make use of it from then. The question is no longer just “where is everyone”, but the even harder to explain “where is everyone from all time?”
Okay, that’s the plausibility question. How about the desirability one, which system I’d like to exist?
Hmm. I guess I’d give the same answer, the “no affecting your own timeline” form. I think that if you could affect your own timeline, that probably some kind of incident in the future – only takes one – would be likely to have mucked up things sufficiently to wipe out civilization, and we probably wouldn’t be around to even be pondering the matter.
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
Branch off probably
