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
I don’t need anymore subscriptions, thank you.
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.
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.
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.
I subscribe to multiverse theory. It’s probably the safest route and probably most likely.
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).
Branch off probably
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.
The current scientific theory is that time exists across space in cones that would require one to move faster than the speed of light to alter. Going to go with that one for now since I have no idea personally.
Light cones aren’t exactly literal cones of time, they are an abstraction to help us understand the mathematics of time and space. (Assuming you are talking about Penrose diagrams.)
Yes, it was light cones. I was half remembering the uni module I did on the philosophy of time a decade ago. We spent more time on the grandfather paradox than the actual science!
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.
Wormholes. Travel some place faster than light and see light from the past from your source of travel when you arrive, travel again back to your original spot and theoretically you travel backwards in time to before the light from the past that you just saw was even produced yet. Might work the same for just seeing the future if you glimpse through a wormhole that leads to someplace in the future by doing an Allie oop to further into the future someplace far away, then back to someplace in your future but your destinations past. Speed and gravity both impact time. A wormhole fits that description to a T.
Only 1 timeline matters. You’re own. Everything else becomes fluid around your timeline when you time travel.
The timeline IS fragile, but the whole of existence is not in regards to time travel. If you go into the past and change it, the timeline changes, but only because the original timeline had you going back and changing it. You can see yourself. You can interact with yourself, but if everything is exactly as it should be you really don’t want to go mucking around and find yourself in a world where the south lost the civil war but things are thousands of times worse and you killed the ancesotor of the inventor of time travel after breaking your machine and can no longer access the timeline to fix any issues you may have caused.
Removed by mod
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.
Oh, I’ll have to watch that
“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.
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.
I like the one where the motion of the universe is not accounted for, so the travelers drop into empty space. But someone figures out how to use that to travel through space.
Time Wars are fun though. Each prime timeline moving others toward them.
Be a potentially energy-efficient way to exit a gravity well in a spacecraft if you could exploit that and it doesn’t require too much energy. Instead of launching a spacecraft, just send it back in time to when a point was no longer in that well.
EDIT: if the above conditions hold (it’s possible and requires less energy than launch), you also have an infinite-energy-production machine, because you can obtain more potential energy than you are expending energy to time-travel.
If you screw up the calculation, your time machine can also end up deep under the mantle of the Earth. That would be a pretty spicy way to travel.
