Author Topic: Any resolutions to FTL paradoxes?  (Read 149969 times)

Offline hop

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Re: Any resolutions to FTL paradoxes?
« Reply #60 on: 07/23/2017 05:36 am »
FWIW, here's physicist Matthew Buckley's (https://twitter.com/physicsmatt) take on explaining why FTL requires giving up relativity or causality http://www.physicsmatt.com/blog/2016/8/25/why-ftl-implies-time-travel

Offline ppnl

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Re: Any resolutions to FTL paradoxes?
« Reply #61 on: 07/23/2017 05:40 am »

Well you could just allow time travel but make it a subjective thing. For example you could travel back in time to meet your own grandfather. But to everyone who saw you leave you would just disappear never to be seen again. To you it would seem you were in a universe exactly like the one you left except you are in the past and your grandfather is still alive. No need to kill him since you are unlikely to be born in this universe anyway. Thus you can create no paradoxes in the universe that you leave but you still have them in the universe that you arrive in.

It would have the same character as the subjective nature of quantum wave collapse. To us out here a cat in a box can be in superposition. But inside the box the cat knows very well if it is alive or dead. As long as we and the cat are thermodynamically separated - and as a practical matter that is impossible - then we and the cat can disagree on its superposition. The cat that is alive is in some sense in a different universe as the cat that is dead and when we open the box we simply appear in a universe consistent with our observations.

Offline meberbs

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Re: Any resolutions to FTL paradoxes?
« Reply #62 on: 07/23/2017 05:52 am »
It seems the problem is very similar to the Twins Paradox. See attached image I found online. I added the red and orange arrows to represent ship 1 and ship 2. However, this diagram is for 0.6c not 0.7c as we were discussing.

I added the direction of both ships after they exit FTL. This diagram shows the perspective from both sides.
The #1 issue with that diagram is the obvious lack of symmetry. You can see that the red line travels backwards in time in the "outbound" frame, but the orange line should therefore be moving backwards in time in the Earth frame. As part of this you do not show the ship 2 as having as fast of FTL in its frame as ship 1 does.

You also somehow appear to have ship 2 travelling at light speed or close to it after its FTL leg (in its frame), rather than at rest. To me this mostly is just more evidence you don't know what you are talking about.

I attached a modified version. I included a little bit before each FTL jump as well, since the symmetry is more obvious that way. I also gave the second ship a just slightly faster FTL to show the time travel effect. The less powerful the FTL, the faster the relative velocity ship 2 needs to have to start with to enable full time travel, and you appear to have picked a set of values that would have caused ship 2 to arrive at the same time ship1 left if you had drawn the diagram consistently. (This is an interesting situation in itself, as it means for the whole journey, ship 2 would be flying directly aside ship 1, despite them moving in "opposite" directions.)

Offline KelvinZero

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Re: Any resolutions to FTL paradoxes?
« Reply #63 on: 07/23/2017 06:38 am »
FWIW, here's physicist Matthew Buckley's (https://twitter.com/physicsmatt) take on explaining why FTL requires giving up relativity or causality http://www.physicsmatt.com/blog/2016/8/25/why-ftl-implies-time-travel
Another possible solution would be to give up free will.
https://en.wikipedia.org/wiki/Novikov_self-consistency_principle
Im not particularly enthused by that solution, but it is interesting to think what it would even look like.

If I was in a universe like that, I would buy a lottery ticket every day and then tell myself, today I am either going to win the lottery or create a paradox. In a universe like that, I guess you win the lottery.

On the other hand I have heard it is more likely to be struck by lightning than to win the lottery, so perhaps this would not be such a great idea.  :)

Offline ppnl

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Re: Any resolutions to FTL paradoxes?
« Reply #64 on: 07/23/2017 07:23 am »

Another possible solution would be to give up free will.


Yes but as the wiki pointed out it isn't clear how you can justify or even define free will even without time travel. So it isn't clear you are giving up anything. I smell robot.


Offline KelvinZero

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Re: Any resolutions to FTL paradoxes?
« Reply #65 on: 07/23/2017 10:22 am »
Sorry. Don't know the reference. If this is a reference to "Mr Robot", no spoilers please because I intend to watch that some time.

Does anyone know if you can make a single FTL jump and then always decide to implement a paradox? If not, it seems semi plausible to avoid paradoxes by making FTL only operate if no choice afterwards would cause a paradox. For example, If you have sent an observer along your route at relativistic speeds to create a paradox, it disrupts FTL and you don't make the trip. This is a bit like fate limiting free will, but more palatable since it only happens at this one point, and we are all used to having our free will limited at airports.

I realise that on one level that sounds really arbitrary. On the other hand it is not much weirder than the problem of the observer in quantum mechanics collapsing waveforms though the act of observation.

Offline ppnl

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Re: Any resolutions to FTL paradoxes?
« Reply #66 on: 07/23/2017 04:48 pm »
Sorry. Don't know the reference. If this is a reference to "Mr Robot", no spoilers please because I intend to watch that some time.

Does anyone know if you can make a single FTL jump and then always decide to implement a paradox? If not, it seems semi plausible to avoid paradoxes by making FTL only operate if no choice afterwards would cause a paradox. For example, If you have sent an observer along your route at relativistic speeds to create a paradox, it disrupts FTL and you don't make the trip. This is a bit like fate limiting free will, but more palatable since it only happens at this one point, and we are all used to having our free will limited at airports.

I realise that on one level that sounds really arbitrary. On the other hand it is not much weirder than the problem of the observer in quantum mechanics collapsing waveforms though the act of observation.

Really dude? You don't recognize "The Big Bang Theory"? Your nerd cred just went negative. Watch the video I posted. It stands alone and will spoil nothing.

A single FTL jump will not cause a paradox. It will look like time travel to an observer in another frame of reference but you have a space like distance between you and your past so you can't immediately cause a paradox. To cause a paradox you have to accelerate your ship to some relative velocity to your original frame. Then when you jump home you will arrive before you left. That's where the paradoxes start.

Your suggestion to limit paradoxes sounds like the mechanism used by Dr. Who. Kind of clumsy, arbitrary and contrived and really ultimately making no sense at all.

Offline KelvinZero

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Re: Any resolutions to FTL paradoxes?
« Reply #67 on: 07/23/2017 11:14 pm »
A single FTL jump will not cause a paradox. It will look like time travel to an observer in another frame of reference but you have a space like distance between you and your past so you can't immediately cause a paradox. To cause a paradox you have to accelerate your ship to some relative velocity to your original frame. Then when you jump home you will arrive before you left. That's where the paradoxes start.
I thought you could impliment a paradox with a single FTL trip, but I couldn't think of an example. If events A and B are synchronized by a pulse of light emitted exactly halfway between them, it does not seem that any lightspeed signal could get from A to B or vice versa in less time.

Can anyone else confirm whether or not FTL paradoxes always involve multiple FTL usages to implement?

Offline ppnl

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Re: Any resolutions to FTL paradoxes?
« Reply #68 on: 07/23/2017 11:54 pm »
A single FTL jump will not cause a paradox. It will look like time travel to an observer in another frame of reference but you have a space like distance between you and your past so you can't immediately cause a paradox. To cause a paradox you have to accelerate your ship to some relative velocity to your original frame. Then when you jump home you will arrive before you left. That's where the paradoxes start.
I thought you could impliment a paradox with a single FTL trip, but I couldn't think of an example. If events A and B are synchronized by a pulse of light emitted exactly halfway between them, it does not seem that any lightspeed signal could get from A to B or vice versa in less time.

Can anyone else confirm whether or not FTL paradoxes always involve multiple FTL usages to implement?

Well maybe it can if your warp drive can warp to a point in space time that is local in space but back in time. Such a thing is usually just called a time travel machine. Time travel machines can enable effective FTL travel. Just travel back in time eight years and then go to Alpha Centauri at half the speed of light. You will effectively have gotten there instantly.

And it depends on what you mean by paradox. If you travel faster than light then an observer will see you as being in two different places at once. That seems like a paradox. But usually the word paradox is used to refer to when you interact with your own past.


Offline KelvinZero

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Re: Any resolutions to FTL paradoxes?
« Reply #69 on: 07/24/2017 03:10 am »
Well maybe it can if your warp drive can warp to a point in space time that is local in space but back in time. Such a thing is usually just called a time travel machine. Time travel machines can enable effective FTL travel. Just travel back in time eight years and then go to Alpha Centauri at half the speed of light. You will effectively have gotten there instantly.

And it depends on what you mean by paradox. If you travel faster than light then an observer will see you as being in two different places at once. That seems like a paradox. But usually the word paradox is used to refer to when you interact with your own past.
That is all granted and not really a concern. Neither of us can think of a way to implement a paradox with one FTL 'jump'. Im just waiting to see if anyone else can propose a way.

I think you can definitely do it with multiple instantaneous communications, even if you limit them all to a privileged reference frame. (edit: I should sit down and reconfirm that. No time at the moment)

Here is someone who thinks you can solve FTL paradoxes by restricting it to a special reference frame:
http://www.physicsguy.com/ftl/html/FTL_part4.html
« Last Edit: 07/24/2017 09:16 am by KelvinZero »

Offline WarpTech

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Re: Any resolutions to FTL paradoxes?
« Reply #70 on: 07/24/2017 04:22 am »
The #1 issue with that diagram is the obvious lack of symmetry. You can see that the red line travels backwards in time in the "outbound" frame, but the orange line should therefore be moving backwards in time in the Earth frame. As part of this you do not show the ship 2 as having as fast of FTL in its frame as ship 1 does.

You also somehow appear to have ship 2 travelling at light speed or close to it after its FTL leg (in its frame), rather than at rest. To me this mostly is just more evidence you don't know what you are talking about.
...

Thanks for the effort. I see my errors and what you mean by symmetry. I've updated the diagrams again to show the "now" line in both frames, and what a trip would look like "at" the speed of light with a warp drive in both frames. You can see that a small increase in the speed of light is not going to cause a paradox. However, there is a forbidden zone between the two "now" lines.

The key to resolving the paradox is; the two clocks are compared when ship 1 exits FTL, whoever has elapsed the most time is correct, and the other is wrong. Using a path integral approach, we want to do the variation of the path to maximize the worldline through space-time. The maximal path is the one that is the correct path.

What causes the paradox is that Special Relative is about the "Special Case" where there is symmetry. That is when the Lorentz transformations are applied. But it's not always symmetrical. Take two observers with clocks, one far from any massive objects and one hovering near the event horizon of the black hole. From the perspective of the distant observer, the clock near the EH is running slow, experiencing gravitational time dilation. The observer near the event horizon does not see the other clock running slow, he sees it running fast! It's not symmetrical. Now, if we consider the possibility that inertial mass and gravitational mass are the same thing, and that time dilation due to gravity and time dilation due to inertia content are caused by the same thing, then these non-symmetrical situations would be the General solution, and the special case would be symmetry.

This may not be as far fetched as you think. Quantum Electrodynamics (QED) shows us that the vacuum has a spectral energy density that is as a function of frequency, f3. As a result, the EM vacuum ZPF does not exert any forces on matter and we cannot measure motion relative to this vacuum. However, this is not a unique spectral energy density! Its value is degenerate. To paraphrase P.W. Milonni; Any spectral energy proportional to f3 will work. Conclusion, the EM vacuum can have many different spectral energy densities, depending on the distribution of matter and energy in the vicinity. The rate at which matter interacts with this field causes "damping" of the wave functions. Gravity is the gradient in this damping factor. The local gravitational field sets a local baseline for the relative damping factor, and motion relative to it increases the damping rate and results in time dilation using the same means for both gravity and motion. Unfortunately, we (mis)interpret this as geometry.





« Last Edit: 07/24/2017 04:51 am by WarpTech »

Offline meberbs

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Re: Any resolutions to FTL paradoxes?
« Reply #71 on: 07/24/2017 06:54 am »
The key to resolving the paradox is; the two clocks are compared when ship 1 exits FTL, whoever has elapsed the most time is correct, and the other is wrong.
What do you not understand about the fact that the Earth frame and the ship 2 initial frame are both correct? Nothing about the ship 1 or Earth frame should cause ship 2 to be unable to FTL in its own frame as fast as ship 1 could in its own frame.

What causes the paradox is that Special Relative is about the "Special Case" where there is symmetry.
It isn't a special case where there is symmetry, it is the only case. If you find an exception to this, you would literally have to rewrite all of modern physics.

That is when the Lorentz transformations are applied. But it's not always symmetrical. Take two observers with clocks, one far from any massive objects and one hovering near the event horizon of the black hole.
There are no general relativistic effects relevant in this situation, even if there were\ it wouldn't prevent the paradox,  and discussing general relativity is pointless when you don't understand special relativity.

I am also going to ignore your comments on QED, since it isn't even a tangent, a tangent would imply that it at some point touched on relevance.

Offline WarpTech

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Re: Any resolutions to FTL paradoxes?
« Reply #72 on: 07/24/2017 07:54 pm »
The key to resolving the paradox is; the two clocks are compared when ship 1 exits FTL, whoever has elapsed the most time is correct, and the other is wrong.
What do you not understand about the fact that the Earth frame and the ship 2 initial frame are both correct? Nothing about the ship 1 or Earth frame should cause ship 2 to be unable to FTL in its own frame as fast as ship 1 could in its own frame.

Are you sure that this is a realistic expectation? If we confine this to our own galaxy, then none of the stars that we've observed within our galaxy have speeds anywhere near 0.6c. Even if there were a planet orbiting a black hole, the last stable orbit is only v = 0.5c and any planet at 0.6c orbit would spiral into the event horizon. So I do not believe that such a situation can arise without Ship 2 having accelerated to >0.6c from a relative speed << c, relative to Earth.

What causes the paradox is that Special Relative is about the "Special Case" where there is symmetry.
It isn't a special case where there is symmetry, it is the only case. If you find an exception to this, you would literally have to rewrite all of modern physics.

I just gave you the basis of such a model. Starting from the BH at the center of the milky way, there is a "baseline" for the rate at which time passes in our galaxy, our solar system, our planet. The "local" baseline is our preferred frame and motion relative to it causes increased damping of the quantum oscillators, leading to time dilation and length contraction such that all observers measure the same value of "c", independent of their relative velocity. It doesn't rewrite ANY physics, it only re-interprets what we know based on QED, instead of the classical, fictitious geometry of empty space. You only need to consider it with an open mind.

Offline meberbs

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Re: Any resolutions to FTL paradoxes?
« Reply #73 on: 07/24/2017 09:02 pm »
Are you sure that this is a realistic expectation? If we confine this to our own galaxy, then none of the stars that we've observed within our galaxy have speeds anywhere near 0.6c. Even if there were a planet orbiting a black hole, the last stable orbit is only v = 0.5c and any planet at 0.6c orbit would spiral into the event horizon. So I do not believe that such a situation can arise without Ship 2 having accelerated to >0.6c from a relative speed << c, relative to Earth.
High mass ratio photon rockets powered by matter-antimatter reactions should be able to reach such high velocities, and the relativistic velocity needed to produce a paradox also depends on the speed of your FTL, and it could be quite low. You are trying to solve this by saying "just don't do the thing that causes a paradox." This is just a non-answer.

I just gave you the basis of such a model. Starting from the BH at the center of the milky way, there is a "baseline" for the rate at which time passes in our galaxy, our solar system, our planet. The "local" baseline is our preferred frame and motion relative to it causes increased damping of the quantum oscillators, leading to time dilation and length contraction such that all observers measure the same value of "c", independent of their relative velocity. It doesn't rewrite ANY physics, it only re-interprets what we know based on QED, instead of the classical, fictitious geometry of empty space. You only need to consider it with an open mind.
You are the one who needs to open up your mind and go learn the basics of special relativity. If you pick one frame to be special, then the speed of light would not be constant between frames. You listed multiple different frames, none of which are "the one special frame", which is obvious from you having listed multiple of them. If you did actually pick a special frame, you would have to rewrite a lot of physics, and you would have a lot of experimental results that you would find impossible to explain.

Please don't talk about a theory of quantum gravity when you don't even get special relativity, it makes you sound both arrogant and ignorant.

Offline WarpTech

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Re: Any resolutions to FTL paradoxes?
« Reply #74 on: 07/24/2017 10:24 pm »
Are you sure that this is a realistic expectation? If we confine this to our own galaxy, then none of the stars that we've observed within our galaxy have speeds anywhere near 0.6c. Even if there were a planet orbiting a black hole, the last stable orbit is only v = 0.5c and any planet at 0.6c orbit would spiral into the event horizon. So I do not believe that such a situation can arise without Ship 2 having accelerated to >0.6c from a relative speed << c, relative to Earth.
High mass ratio photon rockets powered by matter-antimatter reactions should be able to reach such high velocities, and the relativistic velocity needed to produce a paradox also depends on the speed of your FTL, and it could be quite low. You are trying to solve this by saying "just don't do the thing that causes a paradox." This is just a non-answer.

That's not even symmetrical! If a rocket of any kind were "accelerated" to reach such a speed, you must realize that the Earth was not accelerated! One accelerated, physical work was done to it, it's energy content changed. The other did not. That's my point! What you call symmetrical is not symmetrical. You need symmetry to have a paradox. If ship 2 is a rocket that left Earth and accelerated, then Earth has the proper time, and the ship's clock is "really" slower than the Earth clock. The Earth clock is never slower than the Ship 2 clock, regardless what they think they observe. It's not symmetrical and even with FTL, they can't come back before they left.

I just gave you the basis of such a model. Starting from the BH at the center of the milky way, there is a "baseline" for the rate at which time passes in our galaxy, our solar system, our planet. The "local" baseline is our preferred frame and motion relative to it causes increased damping of the quantum oscillators, leading to time dilation and length contraction such that all observers measure the same value of "c", independent of their relative velocity. It doesn't rewrite ANY physics, it only re-interprets what we know based on QED, instead of the classical, fictitious geometry of empty space. You only need to consider it with an open mind.
You are the one who needs to open up your mind and go learn the basics of special relativity. If you pick one frame to be special, then the speed of light would not be constant between frames. You listed multiple different frames, none of which are "the one special frame", which is obvious from you having listed multiple of them. If you did actually pick a special frame, you would have to rewrite a lot of physics, and you would have a lot of experimental results that you would find impossible to explain.

Please don't talk about a theory of quantum gravity when you don't even get special relativity, it makes you sound both arrogant and ignorant.

There is no "one special frame". They are all relative. Our "local" frame is our preferred frame, because it sets the rate at which time passes on Earth. That's all I'm saying. This is perfectly consistent with the tenants of SR. It would not require re-writting any physics. It's just a different interpretation of what we know. You sound like a child when I tell you it doesn't affect physics and you insist that it does. You don't know that, you haven't done the work to claim it does, I have and it doesn't. Read my paper on QG, and try to understand it and you will see that there is no difference between gravitational time dilation and SR time dilation. The mechanism which makes this possible is the same in both phenomenon. "Geometry" is just one interpretation of it, but that's all it is; an interpretation. There are others...


Offline meberbs

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Re: Any resolutions to FTL paradoxes?
« Reply #75 on: 07/24/2017 11:03 pm »
That's not even symmetrical! If a rocket of any kind were "accelerated" to reach such a speed, you must realize that the Earth was not accelerated! One accelerated, physical work was done to it, it's energy content changed. The other did not. That's my point! What you call symmetrical is not symmetrical.
After the rocket has finished accelerating, there is no way anyone on the rocket, on the Earth, or in any other inertial reference frame would be able to tell that it hadn't always been moving at that speed. The acceleration could have been to ship 1 instead, or half way to both. It doesn't matter.

And don't bring up the so-called "twin paradox." That is a case where people who arrive at a paradox fail to account for the effect of the acceleration on the time experienced by the twin who is accelerating. In this case, the paradox does not care if the people on the ship their trip as lasting 1 million years, or 1 second. All that matters is that a drive exists that can move between 2 space-like separated points.

There is no "one special frame". They are all relative.
Exactly.

Our "local" frame is our preferred frame, because it sets the rate at which time passes on Earth.
Special frame and preferred frame mean exactly the same thing in this context. There is no preferred frame.

You state one of the basic principles of relativity and contradict it in the next sentence. You don't understand why FTL is time travel even after being shown diagrams that demonstrate it clearly, when every competent physicist on the planet understands this. It would be a waste of time to read anything you write about actually complicated topics like general relativity or quantum mechanics.

there is no difference between gravitational time dilation and SR time dilation.
General relativity is just the full version of special relativity, of course time dilation is the same thing in both. You treating this statement like it is some kind of revelation or thinking that it changes anything I have already said is just further evidence that you don't understand the relevant topics.

Offline dustinthewind

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Re: Any resolutions to FTL paradoxes?
« Reply #76 on: 07/25/2017 01:52 am »
That's not even symmetrical! If a rocket of any kind were "accelerated" to reach such a speed, you must realize that the Earth was not accelerated! One accelerated, physical work was done to it, it's energy content changed. The other did not. That's my point! What you call symmetrical is not symmetrical.
After the rocket has finished accelerating, there is no way anyone on the rocket, on the Earth, or in any other inertial reference frame would be able to tell that it hadn't always been moving at that speed. The acceleration could have been to ship 1 instead, or half way to both. It doesn't matter.

And don't bring up the so-called "twin paradox." That is a case where people who arrive at a paradox fail to account for the effect of the acceleration on the time experienced by the twin who is accelerating. In this case, the paradox does not care if the people on the ship their trip as lasting 1 million years, or 1 second. All that matters is that a drive exists that can move between 2 space-like separated points.

There is no "one special frame". They are all relative.
Exactly.

Our "local" frame is our preferred frame, because it sets the rate at which time passes on Earth.

Special frame and preferred frame mean exactly the same thing in this context. There is no preferred frame.

You state one of the basic principles of relativity and contradict it in the next sentence. You don't understand why FTL is time travel even after being shown diagrams that demonstrate it clearly, when every competent physicist on the planet understands this. It would be a waste of time to read anything you write about actually complicated topics like general relativity or quantum mechanics.


there is no difference between gravitational time dilation and SR time dilation.
General relativity is just the full version of special relativity, of course time dilation is the same thing in both. You treating this statement like it is some kind of revelation or thinking that it changes anything I have already said is just further evidence that you don't understand the relevant topics.

I won't refer to them all but there are better ways than to throw insults.  If the conversion could continue without the need to justify oneself, by insulting others, it would be of benefit to the forum.  Thanks.

Because the topic of frames of space was brought up.  One such detector might be a Sagnac Interferometer.

The rotation thus measured is an absolute rotation, that is, the platform's rotation with respect to an inertial reference frame.

It seems to be an absolute detector of space not rotating.  If we build one in rotating space (https://en.wikipedia.org/wiki/Lense%E2%80%93Thirring_precession) (around earth maybe), and the speed of light is faster one way around than the other the Sagnac Interferometer would need to rotate at the same rate as space to not detect rotation - thus rotating with space.  (Not very likely this has been done yet, but there seems to be no reason for it not to be.)

Quote from: https://scholar.google.com/scholar?cluster=5939725836829968164&hl=en&as_sdt=0,26
Gravitomagnetic effects
M. L. Ruggiero, A. Tartaglia
Satellites ring. An idea to verify the GR corrections to the Sagnac effect
is to make use of a ring of orbiting satellites (such as those belonging to the
GPS or to the future European Galileo system). A stationary ring configuration
of satellites can be the way to force the light beams to run in a closed circuit
around the Earth, both in co-rotating and counter-rotating direction. The time
difference in the propagation times should reproduce the effect expressed by formula
(42)-(47), once the much bigger classical Sagnac effect has been subtracted
out. Of course here too the technical details need to be thoroughly worked out.

« Last Edit: 07/25/2017 02:37 am by dustinthewind »

Offline WarpTech

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Re: Any resolutions to FTL paradoxes?
« Reply #77 on: 07/25/2017 04:43 am »
That's not even symmetrical! If a rocket of any kind were "accelerated" to reach such a speed, you must realize that the Earth was not accelerated! One accelerated, physical work was done to it, it's energy content changed. The other did not. That's my point! What you call symmetrical is not symmetrical.
After the rocket has finished accelerating, there is no way anyone on the rocket, on the Earth, or in any other inertial reference frame would be able to tell that it hadn't always been moving at that speed. The acceleration could have been to ship 1 instead, or half way to both. It doesn't matter.

And don't bring up the so-called "twin paradox." That is a case where people who arrive at a paradox fail to account for the effect of the acceleration on the time experienced by the twin who is accelerating. In this case, the paradox does not care if the people on the ship their trip as lasting 1 million years, or 1 second. All that matters is that a drive exists that can move between 2 space-like separated points.

Apparently we have different assumptions (realistic vs false) regarding the setup of this problem. Which is why you insist there is a paradox. You are wrong in that I do see why there is a paradox AND how to resolve it. You see only a symmetrical problem, which is like it or not, "identical" to the Twin paradox. What I'm saying that the interpretation you have is wrong. The past does not exist for anyone to travel backwards in time. Causality only requires that there be a finite coordinate speed of light, GR says that the coordinate speed of light is not constant, it's a variable around massive objects. The speed of light in high orbit is "faster" than it is on the surface of the Earth. No causality is broken by this, yet relative to a light signal in vacuum on Earth, the same signal in space far from matter travels a little faster.

In formulating this problem, Ship 1 and Ship 2 are "identical" and both originate from Earth. In accelerating Ship 2 to 0.6c, it's relative mass/energy has increased to 125% of that of Ship 1, it's clock has slowed down and it's length has contracted. Nothing changed on Ship 1, it's still in the hanger on Earth. This is not a symmetrical problem. Ship 2 is now heavier than Ship 1 because WORK was done to Ship 2 to accelerate it, that was not done to Ship 1. One clock is slowed, the other is not!

You would not say that Ship 2 can accelerate at the same rate as Ship 1, if Ship 2 were down in a gravity well, equivalent to a gravitational potential of;

2GM/r = (0.6c)2

It would not, because the two ships are in different physical-vacuum environments.

there is no difference between gravitational time dilation and SR time dilation.
General relativity is just the full version of special relativity, of course time dilation is the same thing in both. You treating this statement like it is some kind of revelation or thinking that it changes anything I have already said is just further evidence that you don't understand the relevant topics.

It specifically contradicts your belief that there is symmetry in this problem, because in GR, if Ship 2 is in a gravity well and it's clock runs slow, it does not look up at Ship 1 and see it's clock there running slow. It runs fast. Which is identical to the temporal relationship between Ship 1 and Ship 2 when Ship 2 was accelerated to 0.6c.

The space-time diagrams that I provided last night shows the trip of Ship 1 and Ship 2, at the speed "c". If these paths are slightly faster than c, Ship 2 may get to Earth at year 7 on Earth's clock instead of year 8 but, it does not cause a paradox. The paradox only occurs when you "assume" the problem is symmetrical in both frames, when in reality, it is not.

Offline meberbs

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Re: Any resolutions to FTL paradoxes?
« Reply #78 on: 07/25/2017 05:07 am »
That's not even symmetrical! If a rocket of any kind were "accelerated" to reach such a speed, you must realize that the Earth was not accelerated! One accelerated, physical work was done to it, it's energy content changed. The other did not. That's my point! What you call symmetrical is not symmetrical.
After the rocket has finished accelerating, there is no way anyone on the rocket, on the Earth, or in any other inertial reference frame would be able to tell that it hadn't always been moving at that speed. The acceleration could have been to ship 1 instead, or half way to both. It doesn't matter.

And don't bring up the so-called "twin paradox." That is a case where people who arrive at a paradox fail to account for the effect of the acceleration on the time experienced by the twin who is accelerating. In this case, the paradox does not care if the people on the ship their trip as lasting 1 million years, or 1 second. All that matters is that a drive exists that can move between 2 space-like separated points.

There is no "one special frame". They are all relative.
Exactly.

Our "local" frame is our preferred frame, because it sets the rate at which time passes on Earth.

Special frame and preferred frame mean exactly the same thing in this context. There is no preferred frame.

You state one of the basic principles of relativity and contradict it in the next sentence. You don't understand why FTL is time travel even after being shown diagrams that demonstrate it clearly, when every competent physicist on the planet understands this. It would be a waste of time to read anything you write about actually complicated topics like general relativity or quantum mechanics.


there is no difference between gravitational time dilation and SR time dilation.
General relativity is just the full version of special relativity, of course time dilation is the same thing in both. You treating this statement like it is some kind of revelation or thinking that it changes anything I have already said is just further evidence that you don't understand the relevant topics.

I won't refer to them all but there are better ways than to throw insults.  If the conversion could continue without the need to justify oneself, by insulting others, it would be of benefit to the forum.  Thanks.
The parts of my post you highlighted are not insults, to the contrary, they are simply statements of fact.

Would a statement that "every person in the world who isn't blind or colorblind agrees the typical color of the sky is blue" be an insult?

The other statement you highlighted was simply pointing out that if someone thinks that a basic concept in a field is an interesting new statement in that field, they probably aren't actually that familiar with the field.

If you think there was some kind of insult there, you report it to the mods, but all I did was state facts.

Also, I have no idea why you bring up the concept of rotating reference frames, that is just an irrelevant complication. As for inertial reference frames, we have Michelson-Morley type experiments that show they are all equivalent.

Offline meberbs

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Re: Any resolutions to FTL paradoxes?
« Reply #79 on: 07/25/2017 06:03 am »
That's not even symmetrical! If a rocket of any kind were "accelerated" to reach such a speed, you must realize that the Earth was not accelerated! One accelerated, physical work was done to it, it's energy content changed. The other did not. That's my point! What you call symmetrical is not symmetrical.
After the rocket has finished accelerating, there is no way anyone on the rocket, on the Earth, or in any other inertial reference frame would be able to tell that it hadn't always been moving at that speed. The acceleration could have been to ship 1 instead, or half way to both. It doesn't matter.

And don't bring up the so-called "twin paradox." That is a case where people who arrive at a paradox fail to account for the effect of the acceleration on the time experienced by the twin who is accelerating. In this case, the paradox does not care if the people on the ship their trip as lasting 1 million years, or 1 second. All that matters is that a drive exists that can move between 2 space-like separated points.

Apparently we have different assumptions (realistic vs false) regarding the setup of this problem. Which is why you insist there is a paradox. You are wrong in that I do see why there is a paradox AND how to resolve it. You see only a symmetrical problem, which is like it or not, "identical" to the Twin paradox. What I'm saying that the interpretation you have is wrong. The past does not exist for anyone to travel backwards in time. Causality only requires that there be a finite coordinate speed of light, GR says that the coordinate speed of light is not constant, it's a variable around massive objects. The speed of light in high orbit is "faster" than it is on the surface of the Earth. No causality is broken by this, yet relative to a light signal in vacuum on Earth, the same signal in space far from matter travels a little faster.
"which is like it or not, "identical" to the Twin paradox."
This statement disproves your claim that you see why there is a paradox.
The twin paradox is not a paradox, it is people misusing special relativity, and not recognizing that there are 3 relevant inertial frames that need to be considered. This situation only involves 2 relevant inertial frames, and really is a paradox if you allow FTL travel.


In formulating this problem, Ship 1 and Ship 2 are "identical" and both originate from Earth.
Both originating from Earth is both optional and irrelevant.

In accelerating Ship 2 to 0.6c, it's relative mass/energy has increased to 125% of that of Ship 1, it's clock has slowed down and it's length has contracted. Nothing changed on Ship 1, it's still in the hanger on Earth. This is not a symmetrical problem.
In ship 2's frame, everything you said about ship 2 is true about ship 1, except the hangar on Earth part. If they started in deep space with no nearby reference points, and the crews of each ship were unconscious during the acceleration, no measurement they could do onboard the ship, or by observing the other ship could tell them which one had accelerated. (They could look at far away stars and see the redshift of course, but those were all moving at different velocities to start with as well, and in no way affect the problem. )

I already said this, but I will keep repeating it until you read it, because you did not actually addres this statement:
Quote
After the rocket has finished accelerating, there is no way anyone on the rocket, on the Earth, or in any other inertial reference frame would be able to tell that it hadn't always been moving at that speed. The acceleration could have been to ship 1 instead, or half way to both. It doesn't matter.


there is no difference between gravitational time dilation and SR time dilation.
General relativity is just the full version of special relativity, of course time dilation is the same thing in both. You treating this statement like it is some kind of revelation or thinking that it changes anything I have already said is just further evidence that you don't understand the relevant topics.

It specifically contradicts your belief that there is symmetry in this problem, because in GR, if Ship 2 is in a gravity well and it's clock runs slow, it does not look up at Ship 1 and see it's clock there running slow. It runs fast. Which is identical to the temporal relationship between Ship 1 and Ship 2 when Ship 2 was accelerated to 0.6c.
Except there is no gravity well in this problem. In this problem as stated, ship 2 does see ship 1's clock running slow. As I said before go setup this problem by sending both ships off in opposite directions at c/3 (to get 0.6 relative). They are all equivalent, and once the acceleration is done, there is no way to tell it ever happened.

The space-time diagrams that I provided last night shows the trip of Ship 1 and Ship 2, at the speed "c". If these paths are slightly faster than c, Ship 2 may get to Earth at year 7 on Earth's clock instead of year 8 but, it does not cause a paradox. The paradox only occurs when you "assume" the problem is symmetrical in both frames, when in reality, it is not.
Your so called "solutions" are just to not act out the problem. You have suggested adding a gravity well when there is none. You have also just turned down the effectiveness of the FTL drives to almost nothing, without having the ships actually have enough relative velocity for the given amount of FTL to illustrate the paradox.
« Last Edit: 07/25/2017 06:03 am by meberbs »

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