Ask Lemmy

I subscribe to multiverse theory. It's probably the safest route and probably most likely.

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.

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

Infinite branches.

It feels more intuitive, and doesn’t involve any strange problems. It implies that the multiverse has infinite possibilities, they are all realized somewhere, and a time machine allows you to jump between them.

Theory: time is immutable, and the universe exists as a single timeline that repeats itself through a high-dimensional recursive or map-reduce. By “time travel,” you are essentially moving yourself across loops and jumping to a different iteration of this universe.

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.

Like in Black Science, I think time travel would fuck with the fabric of reality. Make it shreddy.

I do not believe in nexus events; there is a personal reason (experience ) I don't expect anyone else to believe based on something I experienced but I don't. ETA: Unfortunately, everything has happened already, and I was very angry about it.

Just watched Arrival again yesterday and that's my other guess. More like your choice of "you have already done it, you can't alter the timeline" but can't go outside your lifetime, time doesn't work the way we think and we can perceive other "times" because they aren't really linear, just some quirk of our perception makes it seem that way, you really exist concurrently all along your existence.

But if some machine was designed to take you before or after your lifetime, it would tear at the fabric of reality (lifetime not exactly the correct word but your existence that has a beginning and end of some sort).

Traveling to the past: You can't go into the past because doing so would change who you are and thus your reason for traveling in the first place. For example, killing Hitler when he was a baby would completely change the world as we know it, thus change you as you are. You might not have been born, or if you were, you wouldn't know who Hitler was, so there was no reason to go into the past, thus your time travel never happened in the first place. It's a paradox via butterfly effect. To underscore this further, you couldn't even change the history of another planet's species simply because it's still a part of your timeline. Same universe.

The only scenario where it might work is going into the past as an impartial observer and not having any impact at all (some kind of magical bubble where you are invisible and no effect on the past). That would be fun, because you get to learn about history firsthand.

An interesting time travel alternative is Trunks' timeline from Dragonball Z, where he went to the past, saved their future, but the androids in his timeline still persisted. This leads me to believe it was not just another time but another dimension (a la Rick and Morty).

Traveling to the future is a bit easier. Technically, with the proper spacecraft, you can go into the future (go sit around Sag A* for a bit), but it would be a future where you weren't around to have an influence in it. It would be like temporarily kidnapping yourself. This might be similar to how people came back five years later after being snapped by Thanos in the MCU.

IMO, the best use of time travel would be to go to the future tomorrow to scan ahead and see what happens (as long as you wouldn't have been needed in that future), then going back to the present time just seconds after you left. So little would have changed that your timeline would remain intact (only your biological clock would be off). So, you might be able to prevent incidents in the world by constantly jumping ahead to see what was going to happen. A future-scanning time traveler might have been able to prevent the recent New Orleans tragedy from happening. They could also be lazy and just learn the winning lottery numbers.

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.

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 one that exists.

Either 1 or 3. I tend to lean towards 3

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

I have a unified theory that includes bits of everything.

• it's possible to communicate in the same timeline between the future and past by using gravity (think something like Interstellar)
• By using gravity as an nondestructive line of communication, it's possible to change events in your current existence without a causal shift or split.
• by sending actual matter into a timeline either ahead or behind where it's supposed to exist it causes a causal shift or split in the timeline. this means you will never be able to see the future and can only contaminate the past enough to damage your present causing an inverted negative effect to your going back in time anyway.
• nexus events can only exist when it has a high gravitational marker attached to it. eg: a star will always go supernova, when doesn't matter as much as the fact that it's unstoppable because the gravitational function it applies on a universal scale across all timelines, known and unknown. think of it like flashing a flashlight into a room filled with mirrors. each mirror is the physical plane of existence for the timeline (the beam of light). the beam will hit the first plane and then bounce off all the others in the order in which the photons scatter. if you could slow down and witness the photons, they wouldn't all hit at the same time nor at the same strength.
• It's only possible to communicate across time using gravity and only if someone has picked up the "receiver" in the past. meaning if we're not listening for the call "now", we will never receive the call from "tomorrow". I think this type of communication is completely within the reach of our technology today and quite possibly is being used today without world knowledge.

Time travel to the future is possible if you travel fast enough. For example, traveling to the nearest galaxy at near-light speed wouldn’t take long for you, though it would take significantly longer for those observing you from Earth.

As for traveling to the past, I imagine it might involve the many-worlds interpretation of quantum physics, where every possible event that can happen does happen in a separate timeline. In this view, you wouldn’t be “changing” the past but rather experiencing an alternate version of it.

I don’t believe in free will, so I’m not concerned about the idea of altering the future by changing the past. If you traveled back in time and killed Hitler, it wouldn’t affect this timeline’s future; instead, you’d simply enter a timeline where that event occurred. The future of your original timeline would remain unchanged.

I think it would be like the first one, except instead of you going back to that time, you would be making a copy of that time to traverse to from your time, similar to how moving a file between devices causes it to be copied.

A relevant quote from a physicist is "some will say it's easier to predict the future than the past, since a single effect can have multiple possible causes but a single cause can only have one possible effect."

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.