Thread: if time travel were possible...

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

It will always be impossible to travel in time. I don't know how anyone has ever believed this is possible. It's a fun idea, but whoever takes it seriously is a horrible thinker.

Originally Posted by Michael

It will always be impossible to travel in time. I don't know how anyone has ever believed this is possible. It's a fun idea, but whoever takes it seriously is a horrible thinker.

do you know the meaning of the word "hypothetical"?

i certainly hope your comment wasnt reffering to me.

you are travelling through time at about the speed of light at this moment. You're just moving forward through it

Originally Posted by PhilosopherStoned

you are travelling through time at about the speed of light at this moment. You're just moving forward through it

yes, but what has that got anything to do with this?

He was responding to Michael saying that it is impossible to travel in time, which it clearly isn't. It is also possible to travel at different speeds, as has been empirically verified.

Originally Posted by slash112

yes, but what has that got anything to do with this?

It was in response to what micheal said. It's a valid point though. People that say time travel is impossible really don't know what they are talking about. I'm not saying that reverse time travel is possible, I would just like an explanation of why it is impossible. My opinion is that it has something to do with the second law of thermodynamics being more fundamental than we've thus far given it credit for as that is pretty much the only thing about physics that isn't time reversible.

Originally Posted by Michael

I don't know how anyone has ever believed this is possible.

You didn't put enough points into Creativity when you made your character.
Also, refer to what PS and Xei have said. Time travel would be like jumping into
a copy of our universe at some other point in time.

Originally Posted by Invader

You didn't put enough points into Creativity when you made your character.
Also, refer to what PS and Xei have said. Time travel would be like jumping into
a copy of our universe at some other point in time.

yeah.. it would be "like" that. have you ever jumped into a copy of our universe? No... it would be like that, but that isn't time travel. the normal time travel would be disappearing, and re-appearing in the same universe, at another time. not in a different universe... you're making up different shit. which would be actual travel, not TIME travel.

No, slash i wasnt referring to you. I was referring to people that believe this is possible, and dedicate their lives to trying to invent time machines and shit.

The other universe would be the current one, at a different time, though.

i heard that if you travel closer to the speed of light, you go forward in time (well, it appears to do so). but i really dont know about back in time, the only way i can think of is going faster than the speed of light which is impossible anyway so thats no use.

Originally Posted by Michael

have you ever jumped into a copy of our universe? No...

I haven't been to the moon, either.

the normal time travel would be disappearing, and re-appearing in the same universe, at another time. not in a different universe... you're making up different shit. which would be actual travel, not TIME travel.

That the universe's timeline would diverge from the original upon your arrival
into the past is an idea that's been tossed around for quite a while. Although
I'm flattered that you think I made that up, I can assure you it's not my idea.

How do you figure? Time never changes... it is just there... its not really even a thing....

according to this, if a jet is flying super fast, I am suddenly aging faster for no reason?

Actually, you'd be aging slower relative to the outside world.

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 PhilosopherStoned

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.

It's called "causality". Maybe you've heard of it? And how is putting "no paradox" as a principle of physics lazy and useless? I was pretty sure that a paradox was by definition unresolvable.

If in the single-world model what goes on in the past has already happened once before the time traveler moves backwards, then anything that goes on has to have the same net effect to make sure the traveler's motivation and memory remain constant. If I was to go back in time to stop WWI from ever starting... then I wouldn't have much reason to stop a war that never started, would I?

Side note: Nice new avatar!

Originally Posted by slash112

no, the faster you go, the slower you age (and the slower you move through time) so it appears you have travelled in time. because if you were to go really fast for what seems like 20 years. millions of years could have passed. i cant remember the reason right now, im too tired to think. its something to do with light, and the fact that the speed of light relative to you doesnt change or some shit like that. (if you move, light is still traveling towards/away from you at the same speed, even though you are moving) i dunno, somehting like that. ask xei, he will probably know

To put it simply, the speed of light doesn't change based on your reference point. Light measures to be moving exactly the same speed whether you are on a supersonic jet, on standing on the ground watching it. Following this, if you were to build a clock based on the time it takes for a beam of light to bounce back and forth between two mirrors, and start moving one mirror away from the other very quickly, the clock would appear to slow down. There's better ways to test it, but that's the simplest explanation I know. It's has been experimentally proven over and over as Xei said above.

You could (ab)use that phenomenon to time travel. Bring yourself up to a speed near the speed of light, and everything around you moves so much faster than you by comparison that when you slow back down, you are effectively in the future. The only downside is that you won't be around for the time you've missed, and there's no going back (so far as we know) once you're done with the future.

Originally Posted by Licity

It's called "causality". Maybe you've heard of it? And how is putting "no paradox" as a principle of physics lazy and useless? I was pretty sure that a paradox was by definition unresolvable.

If in the single-world model what goes on in the past has already happened once before the time traveler moves backwards, then anything that goes on has to have the same net effect to make sure the traveler's motivation and memory remain constant. If I was to go back in time to stop WWI from ever starting... then I wouldn't have much reason to stop a war that never started, would I?

Let's say that I want to kill myself in the past. I just watched the inglorious bastards a few days ago, so lets say that I plan on doing it with a baseball bat blow to the head. The question is at what point does causality prevent me from doing that? And how does it do so without preventing the causality of my neurons telling my muscles to make the swing? So there's a contradiction. Which chain of causality is broken? The only way around that (that I can see at least) is a new force which would allow me to swing but then stop the bat from hitting my head by putting up a force field or something. But now we are postulating a new physical force.

The reason that it's lazy and useless is that it is so broad and powerful. It leaves us with the choice of introducing a new law of physics or claiming that time travel is impossible. It's not a very satisfying reason for the latter though and the first is ridiculous in the absence of experimental reasons for thinking that it might be so. If time travel is impossible, then we would want to work it out based on the fundamental structure of space and time in conjunction with the known laws of physics.

Originally Posted by Licity

Side note: Nice new avatar!

thanks.

I realized that "Law" get's applied to newtons work but nothing in relativity or quantum mechanics which is funny because we know that newtons "laws" are off for high speeds/energy and small objects. Tradition I guess.

Originally Posted by PhilosopherStoned

Let's say that I want to kill myself in the past. I just watched the inglorious bastards a few days ago, so lets say that I plan on doing it with a baseball bat blow to the head. The question is at what point does causality prevent me from doing that? And how does it do so without preventing the causality of my neurons telling my muscles to make the swing? So there's a contradiction. Which chain of causality is broken? The only way around that (that I can see at least) is a new force which would allow me to swing but then stop the bat from hitting my head by putting up a force field or something. But now we are postulating a new physical force.

The reason that it's lazy and useless is that it is so broad and powerful. It leaves us with the choice of introducing a new law of physics or claiming that time travel is impossible. It's not a very satisfying reason for the latter though and the first is ridiculous in the absence of experimental reasons for thinking that it might be so. If time travel is impossible, then we would want to work it out based on the fundamental structure of space and time in conjunction with the known laws of physics.

Well, let's say you happen to have a time machine and are going to try just that. You don't remember a copy of yourself about to hit you in the head, do you? That means something foiled your attempt before you even got to your past self. Causality doesn't need to employ a new force to work, there is no supernatural power that forces cause and effect to behave. Remember that you trying to kill yourself already happened, so any more tries you make won't be in your memory. It's not that the past changes to accommodate your attempt to kill yourself, it's that the past has always included that attempt and you are just fulfilling continuity.

Originally Posted by Licity

Well, let's say you happen to have a time machine and are going to try just that. You don't remember a copy of yourself about to hit you in the head, do you? That means something foiled your attempt before you even got to your past self. Causality doesn't need to employ a new force to work, there is no supernatural power that forces cause and effect to behave. Remember that you trying to kill yourself already happened, so any more tries you make won't be in your memory. It's not that the past changes to accommodate your attempt to kill yourself, it's that the past has always included that attempt and you are just fulfilling continuity.

actually, i never thought of that, that is a very good point.

infact, i just wrote like tons of stuff and deleted it and over and over again, because everything i think of doesnt work.

Originally Posted by Licity

Well, let's say you happen to have a time machine and are going to try just that. You don't remember a copy of yourself about to hit you in the head, do you? That means something foiled your attempt before you even got to your past self. Causality doesn't need to employ a new force to work, there is no supernatural power that forces cause and effect to behave. Remember that you trying to kill yourself already happened, so any more tries you make won't be in your memory. It's not that the past changes to accommodate your attempt to kill yourself, it's that the past has always included that attempt and you are just fulfilling continuity.

Lets say that I'm a billionaire with a finite but arbitrarily large stash of fusion bombs. Lets further suppose that I decide to send them back one at a time through my time machine in such a manner that they will appear directly behind my past self some arbitrarily small amount of time before detonating. Every one of them breaks down? what happens to them after they fail to explode? I suppose the answer to that is that I didn't decide to do that in the future but what prevents me from doing so?

I sort of agree with UM that this whole argument shows the implausibility of time travel into our own past but I still want to know why. Saying "because it would lead to paradox" just doesn't do it for me. Why can't the universe be paradoxical?

Originally Posted by Licity

To put it simply, the speed of light doesn't change based on your reference point. Light measures to be moving exactly the same speed whether you are on a supersonic jet, on standing on the ground watching it. Following this, if you were to build a clock based on the time it takes for a beam of light to bounce back and forth between two mirrors, and start moving one mirror away from the other very quickly, the clock would appear to slow down. There's better ways to test it, but that's the simplest explanation I know. It's has been experimentally proven over and over as Xei said above.

You could (ab)use that phenomenon to time travel. Bring yourself up to a speed near the speed of light, and everything around you moves so much faster than you by comparison that when you slow back down, you are effectively in the future. The only downside is that you won't be around for the time you've missed, and there's no going back (so far as we know) once you're done with the future.

thanks, that helped me understand that more. i still need to read up on it a bit more, im so interested in this shit.