Thread: if time travel were possible...

well, hypothetically, if time travel were possible, and you went back in time and killed yourself. what would happen?

because if you were to kill yourself you would be dead, which means you couldn't have gone back in time in the first place, which means you couldn't have killed yourself which means you couldn't have died.

well?

some say the universe would seize to exist, and that a parallel universe would carry on with an alternate way of things (i.e. you decided not to go back in time), some say you would just die.

i am partly asking this to see what you guys think, and partly because maybe there is an actual answer which is most widely believed by scientists.

I have no idea...

But i would think it would be like back to the future when marty goes back in time and when he sees his parents never get together he just starts to dissapear.

Originally Posted by C911

I have no idea...

But i would think it would be like back to the future when marty goes back in time and when he sees his parents never get together he just starts to dissapear.

yes but if he was to deissapear (i.e. never been born in the first place) then there would be noone to stop them from kissing which would mean time would go on as normal and he would still be born, which means he could still go back in time to mess things up so he would dissapear.... but that cycle would carry on in an infinite loop

I think I remember hearing somthing about the actual answer. I think it's that you can kill your past self, but your present self still exists. Which I could imagine the most as actually happening. But then what about all the stuff that you did from the point that you were killed to the point that you went back in to actually kill youself? Like if you would have set your car on fire the next day after you were killed by yourself, would your car still exist when you went back to the future? But I have read a few books that mention something about time, past, and future all being ilusions and the only thing that is constant and exists always is the present.

Originally Posted by sunshineDaydream

I think I remember hearing somthing about the actual answer. I think it's that you can kill your past self, but your present self still exists. Which I could imagine the most as actually happening. But then what about all the stuff that you did from the point that you were killed to the point that you went back in to actually kill youself? Like if you would have set your car on fire the next day after you were killed by yourself, would your car still exist when you went back to the future? But I have read a few books that mention something about time, past, and future all being ilusions and the only thing that is constant and exists always is the present.

good points there

I don't think that there is a definitive answer other than that time travel leads to the paradox that you've brought up in a classical universe. If one goes to the quantum multiverse interpretation of things, then when you go back into your past and kill yourself, time starts moving along an essentially different path in which you don't exist but the path that you came from still exists in the "universal quantum superposition". If it could ever get falsifiable, the multiverse ontology of QM would make a lot of problems like that disappear.

Originally Posted by PhilosopherStoned

I don't think that there is a definitive answer other than that time travel leads to the paradox that you've brought up in a classical universe. If one goes to the quantum multiverse interpretation of things, then when you go back into your past and kill yourself, time starts moving along an essentially different path in which you don't exist but the path that you came from still exists in the "universal quantum superposition". If it could ever get falsifiable, the multiverse ontology of QM would make a lot of problems like that disappear.

mkay...

ill just take your word for it

Originally Posted by slash112

well, hypothetically, if time travel were possible, and you went back in time and killed yourself. what would happen?

because if you were to kill yourself you would be dead, which means you couldn't have gone back in time in the first place, which means you couldn't have killed yourself which means you couldn't have died.

well?

some say the universe would seize to exist, and that a parallel universe would carry on with an alternate way of things (i.e. you decided not to go back in time), some say you would just die.

i am partly asking this to see what you guys think, and partly because maybe there is an actual answer which is most widely believed by scientists.

It's simple. You cannot go back in time and kill yourself. If, for the purpose of this problem, say that there is exactly one timeline we move back and forth along when traveling, you have to deal with self-consistency. If you tried to pull out a gun and shoot yourself, the gun would jam, or you would get distracted, or your past self would survive the shot. If you went back to fix the gun or take care of the distraction, something else would happen to stop you from doing that. The odds of you being able to cause a paradox will be exactly zero. The general idea is, for you to be able to do something in the past, it would have to have always been that way.

That's kind of a cop-out. It creates a paradox in itself, because there's really no reason that you shouldn't be able to kill an ancestor once you've gone back in time. It suggests there'd be some mysterious force guiding you to stop you breaking logic...

Originally Posted by Xei

Well, the fact is time travel (in the sense you mean; going into the past) is impossible, so it's a bit of a non-issue. It's like asking 'if it were possible to turn gravity off, wouldn't that make it possible to violate the first law of thermodynamics?'. Well yes, but you can't turn gravity off.

A possible answer though is that when you change the past you create a whole new timeline and universe, so there's no contradiction.

again, this is all just hypothetical.
but, my point is once you change the the past and create a whole new timeline, (i assume the new timeline is one which you wouldn not exist anymore) then you wouldnt be there to go back in time to kill yourself. which means there is absoloutely nothing that could prevent you from existing any more. which means that wou would exist. but then it comes back to the fact that time would carry on as it would have and you would go back in time and kill yourself, and the loop starts again.

do you get what i mean? am i making any sense?

Originally Posted by Licity

It's simple. You cannot go back in time and kill yourself. If, for the purpose of this problem, say that there is exactly one timeline we move back and forth along when traveling, you have to deal with self-consistency. If you tried to pull out a gun and shoot yourself, the gun would jam, or you would get distracted, or your past self would survive the shot. If you went back to fix the gun or take care of the distraction, something else would happen to stop you from doing that. The odds of you being able to cause a paradox will be exactly zero. The general idea is, for you to be able to do something in the past, it would have to have always been that way.

this is the science section, not the philosiphy or religion section.
there is no scientific reason why that should be true. there may well be a religious/spiritual reason though, which is what you are talking about

again, this is all just hypothetical.
but, my point is once you change the the past and create a whole new timeline, (i assume the new timeline is one which you wouldn not exist anymore) then you wouldnt be there to go back in time to kill yourself. which means there is absoloutely nothing that could prevent you from existing any more. which means that wou would exist. but then it comes back to the fact that time would carry on as it would have and you would go back in time and kill yourself, and the loop starts again.

do you get what i mean? am i making any sense?

Yes, and I understand the paradox, but creating a new universe solves it, because your parents are in the old universe, and they are dead in the new one. No contradiction, no loop.

Originally Posted by Xei

Yes, and I understand the paradox, but creating a new universe solves it, because your parents are in the old universe, and they are dead in the new one. No contradiction, no loop.

oh i see what you mean now.

thats kinda what i meant when i said "a parallel universe would carry on with an alternate way of things (i.e. you decided not to go back in time)". its not completely what i meant, but its along the same lines. i think

Originally Posted by slash112

this is the science section, not the philosiphy or religion section.
there is no scientific reason why that should be true. there may well be a religious/spiritual reason though, which is what you are talking about

Why would you call that philosophy or religion? Something done in the past would, for all intents and purposes of the time traveler, have already had happened. Anything they do would be averted at the last second to avoid paradox, because as we already know, there are no huge glaring paradoxes.

This stuff is all moot if Xei is right about universe copies being produced on traveling, because as long as you are the one from the other universe your ancestry wouldn't need to exist in the new world.

Originally Posted by Licity

Why would you call that philosophy or religion? Something done in the past would, for all intents and purposes of the time traveler, have already had happened. Anything they do would be averted at the last second to avoid paradox, because as we already know, there are no huge glaring paradoxes.

That's pure philosophy. Where did you read that? Some dumb shit makes it into popular physics books...

There would need to be a force preventing you from doing that. What force? Putting forward "no paradox" as a principle of physics is lazy and useless. Lazy because it's too broad and useless because it doesn't tell us what to look for in terms of laws to describe a physical situation.

Originally Posted by Xei

That's kind of a cop-out. It creates a paradox in itself, because there's really no reason that you shouldn't be able to kill an ancestor once you've gone back in time. It suggests there'd be some mysterious force guiding you to stop you breaking logic...

I don't think it's a cop-out at all. If you went back in time to attempt killing your ten-year-old self that would mean when you were ten years old a future version of you also attempted to go back in time and kill you. There doesn't have to be a "mysterious force" involved. The fact that you were not killed by a future you says that he failed for whatever reason. Maybe he got caught by the security system, maybe your father shot him in the face, or maybe he even decided that it was impossible for him to kill you since he was not murdered by himself in his past. It's not that you can't kill a direct blood relative or yourself, it's that you won't due to circumstances that prevented you from being killed by yourself when you were younger. Even though they are basically the same thing in this case, they describe different mindsets.

Of course, it's not like this question will ever be relevant to our lives.

Originally Posted by Black_Eagle

I don't think it's a cop-out at all. If you went back in time to attempt killing your ten-year-old self that would mean when you were ten years old a future version of you also attempted to go back in time and kill you. There doesn't have to be a "mysterious force" involved. The fact that you were not killed by a future you says that he failed for whatever reason. Maybe he got caught by the security system, maybe your father shot him in the face, or maybe he even decided that it was impossible for him to kill you since he was not murdered by himself in his past. It's not that you can't kill a direct blood relative or yourself, it's that you won't due to circumstances that prevented you from being killed by yourself when you were younger. Even though they are basically the same thing in this case, they describe different mindsets.

Of course, it's not like this question will ever be relevant to our lives.

But it doesn't answer the paradox, because, as there is no mysterious force, there are a class of people to whom what you have just said applies, and then there a class of people caught in the paradox because they successfully killed themselves.