Thread: if time travel were possible...

Originally Posted by Invader

I haven't been to the moon, either.



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.

Sorry, didn't mean to give you credit for making up that nonsense. I just used the word "you're" for fun. I am aware that this idea has gone around for a while. I am also aware that you haven't been to the moon.

And, I didn't say that I was in the jet. I meant I am part of the outside world.

Originally Posted by Michael

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?

Maybe the faster you go, the less time it takes, but thats all I notice.

Can you explain more? I'm sure you're correct... It just seems to me that time is unchangeable, and mainly just measurements for us humans

Well, actually you would age slower. If you looked at somebody on the ground, they would be ageing faster. However the speed of a jet is so minute compared to the speed of light that there's really no difference at all. You can work out the coefficient with the formula

1/sqrt(1 - v^2/c^2)

(that's from memory and could be wrong; your speed is v and the speed of light is c).

This is all a consequence of Einstein's Theory of Relativity.

It's one of the most monumental things he ever discovered. You should read about it really because it's one of the greatest discoveries of mankind.

Originally Posted by Xei

Well, actually you would age slower. If you looked at somebody on the ground, they would be ageing faster. However the speed of a jet is so minute compared to the speed of light that there's really no difference at all. You can work out the coefficient with the formula

1/sqrt(1 - v^2/c^2)

(that's from memory and could be wrong; your speed is v and the speed of light is c).

This is all a consequence of Einstein's Theory of Relativity.

It's one of the most monumental things he ever discovered. You should read about it really because it's one of the greatest discoveries of mankind.

I didn't mean that I was in the jet, but this explaination works.

I still don't understand how it's possible though, and I will have to research it. =P I know a little about this theory...

My belief as of now stays the same. That is that time is constant. Time can't be slowed down, sped up, or altared in any way. You can do things inside of time, and even bend space to change the amount of time for things, but you can't do anything to time. Just my opinion I guess.

no thats off. Time travels slower when you approach the speed of light. The whole point is that you are moving through space-time at the speed of light. If you are stationary in the space part of it, the full direction of your motion is through time. If you are moving at the speed of light, then you are not moving through time at all. or at least you're not measuring any time.

Damn: missed the update. What xei said. he even brought the formula

Originally Posted by PhilosopherStoned

no thats off. Time travels slower when you approach the speed of light. The whole point is that you are moving through space-time at the speed of light. If you are stationary in the space part of it, the full direction of your motion is through time. If you are moving at the speed of light, then you are not moving through time at all. or at least you're not measuring any time.

Damn: missed the update. What xei said. he even brought the formula

This is just a theory.

it still takes time for light to get places. and it's still going through the same time that we are in, it's just moving faster. even if you can teleport, you are still going through time at the same rate.

It is the best supported theory of all time. As xei pointed out, it's called special relativity.

No, it has been experimentally confirmed. It's no more a theory than 'the sky is blue' or 'people have two legs' is a theory.

maaaayyyyybbeeee. I said that evolution was proven in the R/S forum (and it hurt) but amongst scientists, let's just say that it's the best supported theory. Keeps us limber.

Originally Posted by Xei

No, it has been experimentally confirmed. It's no more a theory than 'the sky is blue' or 'people have two legs' is a theory.

Why isn't it a law?

What's a law?

As far as I know a law is a specific mathematical relationship such as the inverse square law for attraction between force affected point particles at a distance.

Special Relativity is a set of laws really.

Special relativity is a set of principles. It says that the laws of physics have to be look the same in all inertial frames of reference and that the speed of light is constant. I guess the last one could be called a law but fact would be better terminology IMO

Originally Posted by Xei

As far as I know a law is a specific mathematical relationship such as the inverse square law for attraction between force affected point particles at a distance.

Special Relativity is a set of laws really.

I never knew that really.

I always thought that any theory became a law after proven. =X

Well time to research more of this. It is really REALLY interesting.

Law is pretty much grade school terminology aside from vague references to "the laws of physics" that gets used in casual speech. Principles, postulates, forces and empirical fact are what actually seem to happen in physics. I'm only at advanced undergraduate level except for a little first year graduate general relativity so I could be wrong.

Originally Posted by PhilosopherStoned

Law is pretty much grade school terminology aside from vague references to "the laws of physics" that gets used in casual speech. Principles, postulates, forces and empirical fact are what actually seem to happen in physics. I'm only at advanced undergraduate level except for a little first year graduate general relativity so I could be wrong.

I don't do college nor ever plan on it, so all my learning comes from books/internet basically. Basically I have good "street" smarts and common sense, but I can be an idiot to math and science. thus coming here

I'm not against college or anything. I've just made more money than most surgeons since I was 17 to not really need it.

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 Michael

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?

Maybe the faster you go, the less time it takes, but thats all I notice.

Can you explain more? I'm sure you're correct... It just seems to me that time is unchangeable, and mainly just measurements for us humans

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

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 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.

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.

If you go to what appears to be "back in time" and kill what appears to be "yourself", you are neither back in time nor killing yourself. You are in a parallel universe, in a parallel past, killing a parallel person who mimics you. If you were not killed by yourself in your past, then you are not visiting your past when you do that to your replica. You are somewhere else.

I think the scenario we are discussing proves the impossibility of true time travel.