Ask Lemmy

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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.

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.

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.

Causality fracturing. Partly because observing Mandala effects. Basically causality has inertia and plasticity like matter, so soft changes bend and big changes tear, and inertial mass is also proportional to the time between the incursion and excursion points.

The first one. Specifically because of wave function collapse (ie. The cat is both alive and dead until the box interacts with the universe)

I either could have or could not have travelled back in time to the year 1927. In our present universe, the wave function collapsed and revealed that I didn't. If I went back in time to 1927, I'd essentially be re-rolling the dice, causing the wave function to collapse again, this time revealing that I did in fact move back in time.

Re-rolling the dice doesn't change the initial roll. It's immutable in the fabric of reality. All I'm doing is creating a new universe in which I did travel back in time.

If I were to then move forward again, I'd be in the new timeline, not the original one. There's no going home again. Which is why Sam Beckett was never able to return home. He spent four seasons creating different universes where one person's life was better at the expense of a bunch of others.

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.