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
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.
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.
Primer because Primer. (Video warning and some spoilers for a bunch of different films.)
I don’t know if I would subscribe to it, but it is one of the more interesting ideas for time travel.
Primer spoilers, kinda, xkcd style:
Time travel will never have any effect on anything.
I was just reading this article about a mathematical understanding of closed time-like curves.
In essence, the argument is that time travel to the part is possible with a degree of free will, but you would not be allowed to alter the part in such a way as to remove the motivation for traveling back in time. E.g., it would be like Futurama where Fry kills his grandfather, but he impregnates his grandmother, this allowing himself to be born. The idea is that the timeline would correct itself and ensure that your future self will always return to the past.
I think time travel as a being who perceives one dimensional time linearly is not possible. And for any entity who doesn’t perceive time linearly it would be no different from traveling in a spacial dimension. It’s just travel. Anything that entity does in that point is a permanent fixture to the entities that perceive it linearly.
So yes, if someone could travel in time in the SciFi sense, they wouldn’t be able to change anything in their past experience (direct experience or prior to their perception, but in their event line) because that’s already part of that point in spacetime to anyone who experiences it linearly.
But also, it’s likely that time is not one-dimensional just like we know space is not only three-dimensional. So it is possible that you could end up in a separate “branch” of time that your past self from your perspective will never experience (directly or as past events), because it’s not the same point in spacetime as the event in your direct past timeline. But it’s not like there is a specific set of “branches”. They likely don’t branch off from a single trunk into the other dimension(s) or if they did “branch”, it was at the same time as all other “branches”, the beginning of the universe, not as specific events occur like in SciFi. And the changes you make in those branches were always part of those branches to people who will perceive the future of that timeline.
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
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).
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.
1
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!
Either 1 or 3. I tend to lean towards 3
I subscribe to multiverse theory. It’s probably the safest route and probably most likely.
The past, present, and future do not exist as separate states.
Imagine a vast array of all possible states of matter in the universe. Imagine reality has a finite spacial resolution. With a series of numbers, or even a single very large number, you could provide a unique identifier for every possible arrangement of matter in the universe. The positions of every star and galaxy. The detailed interactions of every quark. Imagine a list or array that would have a number of entries equal to some indecent multiple of “ten to the ten to the ten…” Imagine all these possible states, every possible configuration the matter of the universe could occupy.
Then realize…All of these possible states exist at once. They are all as real as any other. There is no preferred state. They all exist in some vast “10 to the ten to the ten” dimensional spacetime. What we perceive as the flow of time is simply us moving from one of these states to another. But our consciousness cannot move arbitrarily between states. There are elaborate rules on which states you will be able to observe dependent upon the states you previously observed. We call these rules the laws of physics.
So when you travel through time, you are simply altering your path on this vast multiverse of possible realities. There is no “real” reality. They are all real. Every possible configuration of the matter and energies of the universe physically exist concurrently.
There are no timelines to split or erase, because there are no timelines. There are just conscious minds moving through a near-infinite array of possible “nows.” And all of the nows exist simultaneously. There is no real one. From the perspective of a “time traveler,” it will seem like they changed “the future.” But the truth is the very idea of a past, present, and future as distinct entities is madness. We’re just consciousness drifting through the continuum, from one of the near-infinite nows to another.
That’s a really long way to say “the first one”.
I think it’s the 2nd option
It’s just the first one, only specifically a version where all timelines exist and you simply navigate them. I can see how it might feel like the second one because the timelines already exist, but from one’s subjective viewpoint it’s #1.
I think the first one leaves open what you do, as alternate actions lead to an alternate timeline. The second is more “read-only”, similar to what OP laid out.
The only difference between the first option and the response is that the response posits that all possible timelines exist in advance and rather than generating a new timeline with your decisions, you simply navigate to the one that represents them. It’s a distinction without meaning, especially because the first option doesn’t strictly specify whether the timelines existed in advance or not. It simply says “you branch off into another timeline” with no requirement that it be one generated as a result of your actions.
The second option is called “closed loop” or Novikov self-consistency and specifically requires that the outcomes of your choices align with the past already as defined, simply in ways you did not know. It’s what they use in 12 Monkeys and the 3rd Harry Potter book, and it limits free choice, unlike the first option and what the above poster’s response stated.
I think what you’re doing is combining closed-loop and multiverse theories to say that the multiverse theory IS closed-loop simply because the multiverses existed in advance, whereas closed-loop is intrinsically single universe/timeline.
I appreciate those detailed insights, I see where I misunderstood. I need to reread the 3rd HP novel with my son now :)
It’s my favorite of the series, though I hate what JK Rowling turned into. Hope you and your son enjoy!
Hmm don’t really agree, as you can observe different parts of space on different time periods due to light’s finite speed and time dilation and such. Not all parts of space are at the same time simultaneously. Also, relativity tells us that the state you observe is different from the state of another observer. So you can’t really write this number of the universe down (or at least, you can only write your own personal number down but it won’t be the same as anyone else’s number).
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.
