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
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.
That’s called the bootstrap paradox if you want to look that up.
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.
I don’t need anymore subscriptions, thank you.
I like the idea that the timeline you exist in is that and can still be determined but everything that happened in the pasr is set in stone. Future time travel is not possible.
Time travel does exist, but you can only go forward. You just need to approach the speed of light relative to a frame of reference, and you will travel a shorter time span compared to it.
My belief is if you went to the past your actions would fully effect the future, no branches or anything else of course this will create paradoxes but if your a time traveller you will still exist even if you prevent your birth, if then you go back to the future there will be no record of your existence.
Hope that makes sense.
In either scenario, I’m more interested in where the matter you’re made of will come from:
- Either you go to the past and suddenly add additional atoms to the universe.
- All the atoms you’re made of will suddenly be taken from their origin to form you.
- You’ll be made from entirely new atoms created from pure energy meaning your arrival will cost ~6.75 Quintillion as in 10^18 Joules (I eyeballed the speed of light here so don’t @ me).
Its a one way trip. You can never go back to the original universe.
This is my biggest issue with multiverse time travel in popular culture. Somehow they always travel back and forth between 2 of Infinite timelines
Holy existential horror, Batman! By time traveling, you’ve just caused an entire universe full of new alternate-timeline versions of people to pop into existence. What happened to the timeline you left? It must still exist. You couldn’t have been the only consciousness that was experiencing it. To think otherwise is some extreme solipsism. Gosh, did some other time traveler create the timeline you left by entering it? For that matter, are you actually a duplicate, having just popped into existence with the memory of having time-traveled, but the timeline was created by another time traveler?
Alternatively, perhaps it’s another timeline out of an infinite number of possibilities that all co-exist? Yikes! That means there’s an infinity of each person across the multiverse. Therefore, you could just murder everybody within reach, and time travel back before your started the rampage. The lives in a particular timeline don’t matter, there are an infinity more. I think Rick & Morty did an episode with that premise.
What happened to the timeline you left? It must still exist. You couldn’t have been the only consciousness that was experiencing it. To think otherwise is some extreme solipsism.
Why does it need to remain? It seems like solipsism to assume it must remain because it’s your point of origin. If something or someone has the power to drop something into the past why wouldnt it overwrite everything? I don’t see why consciousness even gets applied. The universe keeps on whether I am alive, asleep, or dead.
I see the path of time like a laser beam in a house of mirrors. If someone has the power to add a mirror somewhere. Yep, the whole beam after the fact is a vastly different pattern. Any multiverse would be entirely virtual and theoretical.
Why does it need to remain? Because that timeline was populated by 8 billion human, and who knows how many non-human minds. I think it would be solipsism to think that only your own mind was the “real” one keeping the timeline in existence, and it collapsed because you leave it.
If the time travel power does overwrite everything, all of those minds and all of their subjective experiences are just, nothing? That’s where the existential horror comes in for me.
Oh I agree, it’s horrifying. And I have noooo guarantee that it’s me doing the jump. Don’t misunderstand I am NOT the only real mind in this example. I’m curently just hitching a ride on said laser beam. No guarantees that I will be the same or even exist if somebody so much as moves a pebble into the past from the future.
Existential dread all the way. If we get time travel I think it’s as horrifying a prospect as teleportation on a universal scale with only the traveller maintaining continuity.
I really like the nothing is changeable and travel is possible and anything you do while traveling has already happened / was already going to happen concept
I wouldn’t say I “like” the idea, since it’s one of the most doomed ways for a universe to be, but Greg Egan’s Arrows of Time is a good exploration of this idea.
Branch off probably
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!
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.
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.
Edit: I see I’m being downvoted, so I’ll explain further, if the Universe is deterministic means everything will be the same any time you relive the same time segment, if not, it means even the weather can be different due to aggregation of butterfly effect of different random outcomes in the Universe, and weather being different is already big enough change to be able to influence decisions and course of events. And I’m not meaning weather in the exact same spot you time-traveled to. Even if you restored the exact same state of Universe at some snapshot, if the Universe isn’t deterministic, various random events happening after that point in time can have different outcomes which will aggregate and lead to even more different outcomes in future. Weather might be different the next day and because of that you decided to hide from rain in cafe and met someone there which can completely change your life.
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.
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.
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.
I can think of a couple ways around that, the easiest is that I actually think time travel is impossible. (Like this for example)
If it’s not impossible, then single-timeline travel probably is, and all (backwards) travel would start a new timeline.
Short of that, maybe something ridiculous would have happened when the traveler “first” went back, like one of them tripping or whatever, and the handshake they agreed to try didn’t go as planned, and then “still” didn’t the traveler’s second time. Basically this.
Let’s suppose a time travel event occurs in which an agent with free will travels to their own causal past, and let’s suppose this creates a parallel timeline which can differ from the first (leading to a new version of the agent which creates a third timeline, and so on).
We can consider this time-travel event as a function in which one timeline maps to a successor timeline — or in general, the event is an iterative map from the space of possible timelines to itself. If this map meets a few general criteria, we can apply the fixed point theorem and conclude that, after enough iterations, the process will converge to some fixed point that maps to itself (that is, the agent causes the past of their own timeline, even though they have free will). This timeline maps to itself—but it is also mapped to by an infinite succession of timelines in which the agent is free to alter their successor timeline, converging on one in which their choices cause no further alteration.
At that point, we can dispense with the assumption that time travel creates parallel timelines, and assume instead that the fixed-point, self-causing timeline is the only real one.
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” of OP’s second scenario). 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.
“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.
Oh, I’ll have to watch that
Whichever one is objectively correct based on empirical evidence.
Fun fact: time travel does exist, and I am myself a time traveler. The fact that I’m travelling at one second per second along with everyone else is just a minor detail.
Imagine if someone just naturally traveled through time at like… 1.0005 seconds per second… What would that look like? Would we be able to tell? Would they be able to tell? Would their perception be different?
This is a Relativity thing, isn’t it? Like the astronaut twins sort of…
That’s exactly like being a bit closer to the bottom of a steep gravity well.
Yes, we could tell if they took a precise clock with them. In fact, we have to account for an even smaller discrepancy in order for GPS to work: we here stuck further down in Earth’s gravity well travel through time and extra ten milliseconds or so per year vs. an orbiting satellite.
Are we traveling through time? Or is time simply a universal constant of entropy? Everything you experience is energy flowing from a higher potential to a lower potential, with some “loss” to heat. Without that downward shuffle, a rock balanced on it’s tip is indistinguishable from a time-stopped version of itself.
Basically, time is your body’s sensation of the inevitable terror that is the heatdeath of the universe.
Why would it be less terrifying to be further away from a gravity well?
I think you meant this comment for a different thread.
Nope.
Okay. What did I say about gravity wells?
You implied that life would be more terrifying the faster you traveled through time, like what would happen at the bottom of a gravity well.
Where?
I have always been a fan of stable time loops so I guess option 2 is the best one for me.
One trope I’d like to see more of is loops which are not stable themselves, but are stable as a group. Eg a 2-loop has loop A in which someone goes back in time and changes history leading to a new timeline loop B. Someone in loop B later goes back in time and changes history in a way that turns the timeline back into loop A.
My headcanon is that your option 3 is basically an n-loop that we only see the first few loops of.
You may like the show Dark, if you haven’t already seen it.
Dark
The season 3 story was pretty much why I’m interested in this trope! Although I maintain Dark was not a stable time loop story, it just had the appearance of one.
Whatever it is, I don’t believe paradoxes are possible (other than language ones that basically just confuse any attempts to resolve a statement or set of statements to true or false without breaking any physical laws or causality).
That said, I don’t think an unstable time loop would necessarily be impossible. Eg, you go back in time and kill your grandfather before your father is conceived, which results in you never existing in the timeline, which then means no one is there to go back in time and kill your grandfather, which means the loop disappears and the timeline snaps back to the version where you do go back, and it continually alternates from there.
Not sure if any future outside of the unstable loop would exist, I think that would depend on if there’s a higher dimension of time that these loops could play out over.
Or, if everything experiences the same present at the same time, it’s also possible that after the first loop, it wouldn’t go back to resolve the whole “killer pops out of literally nowhere” because it was in the past and no time traveler is bringing the timeline back to there, so it’s all in the past. Though I think in that case, you wouldn’t disappear after killing your grandfather. You’d just be an enigma that would require going outside of time to understand the origin of.
Tbh though I’m 99% sure time travel just isn’t possible (paradoxes or not), just a fun thing to think about. And no, I don’t consider quantum effects being symmetrical in time to be time travel, they are just cases where you can reverse cause and effect and still have a valid cause and effect sequence.
I subscribe to multiverse theory. It’s probably the safest route and probably most likely.
