Time travel paradox solved

[nutball]

Possibly. I do tend to prod people a bit when they talk about such things to see how far the science ficition virus has penetrated

 

[OpenGL guy]

Stephen Baxter (a physics professer who writes SF) has got around that problem by making a wormhole, and putting one end of it on the above spaceship. The wormhole goes on the subjective trip lasting a few years a the speed of light while thousands of years pass on earth. When you want to go back in time, you just step back through the wormhole which now connects the future back to the past as well as two points in space.

I don't think this works, at least not as intended. By travelling at near the speed of light, time slows down, meaning the people on board age slower. This doesn't mean they are left in the past, however.

 

[Nathan]

Stephen Baxter (a physics professer who writes SF) has got around that problem by making a wormhole, and putting one end of it on the above spaceship. The wormhole goes on the subjective trip lasting a few years a the speed of light while thousands of years pass on earth. When you want to go back in time, you just step back through the wormhole which now connects the future back to the past as well as two points in space.

I don't think this works, at least not as intended. By travelling at near the speed of light, time slows down, meaning the people on board age slower. This doesn't mean they are left in the past, however.

I think the relativistic speeds are necessary to get a time delta between the two ends of the wormhole. This seems like a mechanism for going into the future (by using time dilation), then coming back to the present (via the wormhole) to tell your mates what it was like.

Practical difficulities include:
Creating a wormhole in the first place.
Mounting the wormhole on your ship.
Travelling through the wormhole without dying.

 

[blakjedi]

Books like the Hyperion series explain this as time debt in practical terms but not in terms of science.

In that series they explain time travel as "the void the binds." I easy terms it is subspace everywhere nowhere location. A singular "location" that links all things in time and space. step in one side step out of the other wherever you chose.

Of course though the calculations as to where and when youd end was done by AI that had far outstripped the aggregate intelligience of men centuries before.

 

[Bouncing Zabaglione Bros.]

Stephen Baxter (a physics professer who writes SF) has got around that problem by making a wormhole, and putting one end of it on the above spaceship. The wormhole goes on the subjective trip lasting a few years a the speed of light while thousands of years pass on earth. When you want to go back in time, you just step back through the wormhole which now connects the future back to the past as well as two points in space.

I don't think this works, at least not as intended. By travelling at near the speed of light, time slows down, meaning the people on board age slower. This doesn't mean they are left in the past, however.

No, but the other end of the wormhole is left in the past running on earth subjective time, whereas the one on the ship at lightspeed sees a much slower subjective time. A year passes on the ship, hundred or thousands of years pass on earth, but the two ends of the wormhole remain connected.

I think the relativistic speeds are necessary to get a time delta between the two ends of the wormhole. This seems like a mechanism for going into the future (by using time dilation), then coming back to the present (via the wormhole) to tell your mates what it was like.

Practical difficulities include:
Creating a wormhole in the first place.
Mounting the wormhole on your ship.
Travelling through the wormhole without dying.

That's it exactly. Baxter uses it as a plot device in his book "Ring" if anyone wants to read it. He is a "hard science" SF author, and wrote the authorised sequel to HG Wells "The Time Machine" a few years back called "The Time Ships", which is also very good.

 

[Frank]

No, but the other end of the wormhole is left in the past running on earth subjective time, whereas the one on the ship at lightspeed sees a much slower subjective time. A year passes on the ship, hundred or thousands of years pass on earth, but the two ends of the wormhole remain connected.

So, each point of the wormhole would exist in another time? How could it be possible be a single thing if that would be the case?

But then again, with locality paradoxes, that would be the only way it could exist, joining different pieces of space together. In either case, having all those parts in a different local time as well would complicate matters quite a bit, I think.

 

[OpenGL guy]

Stephen Baxter (a physics professer who writes SF) has got around that problem by making a wormhole, and putting one end of it on the above spaceship. The wormhole goes on the subjective trip lasting a few years a the speed of light while thousands of years pass on earth. When you want to go back in time, you just step back through the wormhole which now connects the future back to the past as well as two points in space.

I don't think this works, at least not as intended. By travelling at near the speed of light, time slows down, meaning the people on board age slower. This doesn't mean they are left in the past, however.

No, but the other end of the wormhole is left in the past running on earth subjective time, whereas the one on the ship at lightspeed sees a much slower subjective time. A year passes on the ship, hundred or thousands of years pass on earth, but the two ends of the wormhole remain connected.

This is exactly what I said! People on the ship can't go back in time at all. While they've aged only a few years, everything else in the universe has aged by much more. Hopping into the wormhole does no good whatsoever because the other end of the wormhole has aged by many years as well!

I think the relativistic speeds are necessary to get a time delta between the two ends of the wormhole. This seems like a mechanism for going into the future (by using time dilation), then coming back to the present (via the wormhole) to tell your mates what it was like.

Practical difficulities include:
Creating a wormhole in the first place.
Mounting the wormhole on your ship.
Travelling through the wormhole without dying.

That's it exactly. Baxter uses it as a plot device in his book "Ring" if anyone wants to read it. He is a "hard science" SF author, and wrote the authorised sequel to HG Wells "The Time Machine" a few years back called "The Time Ships", which is also very good.

He writes books, doesn't mean he's right (write ).

 

[Nathan]

Yeah, the assumption is that the Earth end of the wormhole is stuck in a certain point of time, which I can't see any reason why it would be. It should experience the normal flow of time as OpenGL guy has pointed out. If it were stuck in time, then it would only seem fair to restrict the ship end of the wormhole to being stuck at a point in time too, which means that you can only travel through the wormhole in the instant it is created (because any delay will leave the wormhole in the past), so the whole postulate of dragging a wormhole around behind you is impossible.

 

[Bouncing Zabaglione Bros.]

Well you'd all have to talk to Prof Stephen Baxter about that. Obviously it's a literary construct extrapolated from his background in physics, but he's not writing it as a fact, but as a mechanism to drive the novel forwards.

If you follow his idea that a wormhole has two endpoints connected without traversing the intervening space, then what happens when one is put on a relatavistic spaceship while the other end in anchored in earth orbit? Baxter's wormhole now crosses both space and time without travelling the intervening space.

It's not that difficult a conceptual jump. Given that gravity and velocity affect local subjective time, one end of a wormhole near a planet and another in deep space (or in a deep gravity well) could very well not be experiencing time progressing at the same rate. Baxter postulated that both ends of the wormhole remain connected regardless, and takes that idea to it's very extreme.

Of course if you want to get nit-picky about such fictional constructs, you might as well kill it at the beginning and just say you can't make large wormholes, and even the theoretical microscopic ones only exist for fractions of milliseconds, end even if you could make a wormhole there would be no way to power or guide it.

 

[blakjedi]

you cannot cross space without aging

no such thing as a teleporter like in stargate... by walking through it to another part of the universe... either you've aged or the universe has by the light distance you've traveled... unless you have a flux machine...

but a flux machine require that you have controll of your corresponding atoms at your destination.

 

[Bouncing Zabaglione Bros.]

Yeah, the assumption is that the Earth end of the wormhole is stuck in a certain point of time, which I can't see any reason why it would be. It should experience the normal flow of time as OpenGL guy has pointed out.

The "normal" flow of time is dependent on your subjective viewpoint. Time is slower if you are on a ship travelling near the speed of light compared to time on the surface of the earth, unless you are on the spaceship itself. Time is also slower near a deep gravity well, such as a black hole.

They've even done experiments to show that there is a measurable difference between the time experienced on the earth and in orbit. They synced two atomic clocks, put one in orbit, and the one further out of the gravity well ends up being faster than the one on earth because it is experiencing less gravity and moving faster, so time progresses for the orbiting clock faster than when compared to the one on earth.

It's all about subjective viewpoints.

 

[OpenGL guy]

Well you'd all have to talk to Prof Stephen Baxter about that. Obviously it's a literary construct extrapolated from his background in physics, but he's not writing it as a fact, but as a mechanism to drive the novel forwards.

If you follow his idea that a wormhole has two endpoints connected without traversing the intervening space, then what happens when one is put on a relatavistic spaceship while the other end in anchored in earth orbit? Baxter's wormhole now crosses both space and time without travelling the intervening space.

It's not that difficult a conceptual jump. Given that gravity and velocity affect local subjective time, one end of a wormhole near a planet and another in deep space (or in a deep gravity well) could very well not be experiencing time progressing at the same rate. Baxter postulated that both ends of the wormhole remain connected regardless, and takes that idea to it's very extreme.

Relativistic time travel, when going forward, is akin to cryogenic freezing. Everything around ages, but you don't (or do very slowly). Having a wormhole next to you changes nothing. Everything outside your spaceship (freezer) ages normally while you age slowly. Thus, you can't go back in time. People could step through the wormhole and see that you hadn't aged, but that's the same as you getting off your spaceship in the future.

Of course if you want to get nit-picky about such fictional constructs, you might as well kill it at the beginning and just say you can't make large wormholes, and even the theoretical microscopic ones only exist for fractions of milliseconds, end even if you could make a wormhole there would be no way to power or guide it.

I'm giving you the benefit of the doubt that you could make a wormhole, I am just disputing how it could be used!

 

[Bouncing Zabaglione Bros.]

you cannot cross space without aging

If you were in a starship going at the speed of light or near a gravity well, you would experience time as normal. However, the person still standing on earth would experience time differently. It would be the "same" time, but the person on the spaceship would experience time at a much slower rate than the person who stayed on earth.

You could get in your spaceship, spend ten years travelling at near the speed of light and come back to earth to find that thousands of years have passed. Sure, the person on the spaceship would have aged ten years, but the person who stayed on earth would have aged ten thousand years.

This stuff is basic relativity.

 

[Bigus Dickus]

I'm giving you the benefit of the doubt that you could make a wormhole, I am just disputing how it could be used!

Baxter isn't the first or only one to postulate such usage of a moving wormhole to create the possibility of time travel. Relativity defines the outcome, and the situation does indeed allow travel through time in two directions.

Note however that this usage of a wormhole as a time travel "device" follows the stipulations I defined previously for all such devices. That is, travel is still limited to the span of times during which both ends of the wormhole existed. You could return to the past only so far as the time at which you first created the wormhole, no further. You could travel into the future by a maximum amount equal to the time dilation created by reletavistic effects of the near lightspeed travel.

 

[Bouncing Zabaglione Bros.]

Relativistic time travel, when going forward, is akin to cryogenic freezing. Everything around ages, but you don't (or do very slowly). Having a wormhole next to you changes nothing. Everything outside your spaceship (freezer) ages normally while you age slowly. Thus, you can't go back in time. People could step through the wormhole and see that you hadn't aged, but that's the same as you getting off your spaceship in the future.

It's been a while since I read the book, so I can't quite remember how Baxter justifies it. IIRC, it's something to do with the fact that the two endpoints of the wormhole stay continuously connected, and one end ages a thousand years while the other ages millions of years. Both ends experience different subjective time, but they are still connected and can still be travelled without traversing the intervening space or time. It's more used as reconnasance into the future than a way of travelling back in time, though it does work both ways. I think it hinges on the assumption that wormholes are instantaneous travel from A to B without crossing any distance or taking any time.

 

[Nathan]

http://en.wikipedia.org/wiki/Wormholes

A wormhole could potentially allow time travel. This could be accomplished by accelerating one end of the wormhole relative to the other, and then sometime later bringing it back; relativistic time dilation would result in less time having passed for the accelerated wormhole mouth compared to the stationary one, meaning that anything which entered the stationary wormhole mouth would exit the accelerated one at a point in time prior to its entry. The path through such a wormhole is called a closed timelike curve, and a wormhole with this property is sometimes referred to as a "timehole."

It's actually the opposite of what you suggested. The people on Earth can travel back in time to visit their chums in the spaceship.

 

[blakjedi]

you cannot cross space without aging

If you were in a starship going at the speed of light or near a gravity well, you would experience time as normal. However, the person still standing on earth would experience time differently. It would be the "same" time, but the person on the spaceship would experience time at a much slower rate than the person who stayed on earth.

You could get in your spaceship, spend ten years travelling at near the speed of light and come back to earth to find that thousands of years have passed. Sure, the person on the spaceship would have aged ten years, but the person who stayed on earth would have aged ten thousand years.

This stuff is basic relativity.

Yeah but using a spaceship doesnt work precisely because of basic relativity. As you approach the speed of light you have two basic problems... time and mass. As you move faster your mass increases to the point where your mass becomes infinite... Which leads to the related time problem...

As you approach lightspeed you must burn a certain amount of of fuel to maintain that speed... time moves so slowly on the ship, that you cannot burn enough fuel to increase your speed... as your mass increases you increase the fuel requirements also... if you hit light speed time stops for everyone aboard as well as the fuel so it cant be burnt....

wormholes or portals (rips in space) release you from the requirement to move through space which requires fuel and increases your mass...

 

[OpenGL guy]

http://en.wikipedia.org/wiki/Wormholes

A wormhole could potentially allow time travel. This could be accomplished by accelerating one end of the wormhole relative to the other, and then sometime later bringing it back; relativistic time dilation would result in less time having passed for the accelerated wormhole mouth compared to the stationary one, meaning that anything which entered the stationary wormhole mouth would exit the accelerated one at a point in time prior to its entry. The path through such a wormhole is called a closed timelike curve, and a wormhole with this property is sometimes referred to as a "timehole."

Ok I think I see what they are saying now, but I disagree with the argument. Say you board a spaceship in the year 3000 and leave Earth at near light speed so that 1 year for you is a million years on Earth. If you head out for a million years (1 year for the traveller), you'd be racing the light coming from Earth itself, thus, you wouldn't find out what happened on Earth during that time. However, when you returned, all of that data would come in a hurry (and quite blue shifted as well)! Thus, you would still end up having gone through all the same event, but you just haven't aged much. Now take your wormhole with you. If you travel for a year, people could come through the wormhole and wouldn't see the events on Earth over the last million years, but that doesn't mean they are in the past!

Another way to look at it: Light from the Andromeda Galaxy takes about 2 million years to reach us, thus we see the Andromeda Galaxy as it was 2 million years ago. Does that mean we are in the past? No! The Andromeda Galaxy has aged 2 million years in the process and so have we! When the light reaching us now left the Andromeda Galaxy, that was 2 million years in our past.

Now back to our time traveller. As soon as you try to head back to Earth, you will pass through all the information that happened over the past 2 million years (assuming 1 year travelling out and 1 year back). Thus, people see you only aged 2 years, but there is no going back to the past!

 

[Bouncing Zabaglione Bros.]

wormholes or portals (rips in space) release you from the requirement to move through space which requires fuel and increases your mass...

Obviously I'm simplifying when I keep saying "the speed of light". You'd just have to reach a sizable portion of the speed of light to start seeing relatavistic effects. It's not like I'm going to actually work out the math or anything.

 

[Bouncing Zabaglione Bros.]

http://en.wikipedia.org/wiki/Wormholes

It's actually the opposite of what you suggested. The people on Earth can travel back in time to visit their chums in the spaceship.

I think you're misunderstanding how it's all relative to the subjective viewpoints of the observer(s). Less time passes on the spaceship, but that's subjective time. From the reference point of the earth, the slow moving time in the spaceship has still been moving forwards through time compared to the earth.

It's late now and my head is hurting.