Any resolutions to FTL paradoxes?

[meberbs]

A variable speed of light (VSL) model would be more appropriate. Such a model is the Polarizable Vacuum Model of General Relativity, where the coordinate speed of light is used in the coordinates of a distant observer, c/K. I keep trying to bring this into the conversation and you keep kicking us back to SR and LT's. So let me try one last time.

VSL to me typically would mean a local observer measures a different speed of light. Can we agree to reserve that term for that to avoid confusion (and then proceed to not use it, because neither of us are discussing that. (At least I don't think you mean to.)

There are no theories where a local observer measures something other than "c" locally. VSL is generally accepted as the type of theory I am describing. See R. Dicke 1957...

https://en.wikipedia.org/wiki/Variable_speed_of_light

You are the one who needs to go read that page.
From the specific section you referenced:

Dicke considered a cosmology where c decreased in time, providing an alternative explanation to the cosmological redshift

This is really not at all what you had been saying. (And there is a difference between a local measurement of the speed of light, and the speed of light somewhere else in the universe under this type of theory.)

It would be consistent, but realistically, unless we can achieve speeds 1000's of times > c, it's not gonna happen.

All of your arguments so far for why FTL "can't" happen (to the extent they have any validity) have depended on sufficiently not flat spacetime. You have yet to propose any meaningful limits on your FTL drive, so what is the problem with 1000*c?

No. This is an assertion that time dilation and length contraction depend solely on the relative gravitational potential. Velocity just changes the energy content of the ship "relative" to the CoG base-line it started with.

That last phrase there sounds like you are talking about things having a memory again.

You need to do your homework. I used the Schwarzschild solution of GR as the background metric in my previous post. There was nothing new there except my interpretation. I changed nothing. I have already given you numerous references that refute your assumptions and the conclusions you keep jumping to, that this is somehow inconsistent with GR.

I need to learn something new? After you gave inconsistent explanations of the "twin paradox"? And now pointed me to a wiki page that you apparently need to read yourself.

Equivalence to GR means the exact same predictions as GR. "Interpretation" really can't change these.

[JasonAW3]

Interesting data here;https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.119.080503

Einstein hated "spooky interaction at a distance", because, effectively, it allowed for instantaneous data transmission between two particles, regardless of the distance.  The act of measuring one entangled particle's characteristics, immediately affected the characteristics of the other.

      In other words; one could change the characteristics of two entangled particles, over a distance of light years, INSTANTANEOUSLY by measuring the characteristics of one of the two particles. 

      No time travel involved.  No paradoxes.  Simply quantum physics.

      I'm not saying that this would allow any sort of FTL flight, but it dose lend credence to the possibility that it might be possible, so long as one's arrival does not occur prior to one's departure from one's point of origin.

[meberbs]

Interesting data here;https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.119.080503

Einstein hated "spooky interaction at a distance", because, effectively, it allowed for instantaneous data transmission between two particles, regardless of the distance.  The act of measuring one entangled particle's characteristics, immediately affected the characteristics of the other.

      In other words; one could change the characteristics of two entangled particles, over a distance of light years, INSTANTANEOUSLY by measuring the characteristics of one of the two particles. 

      No time travel involved.  No paradoxes.  Simply quantum physics.

"simple" and "quantum physics" are antonyms. The no communication theorem strictly prevents the "change" from one that there would be any way to tell that the change had happened.

      I'm not saying that this would allow any sort of FTL flight, but it dose lend credence to the possibility that it might be possible, so long as one's arrival does not occur prior to one's departure from one's point of origin.

No, it doesn't really lend credence to the possibility. "so long as one's arrival does not occur prior to one's departure from one's point of origin." is not a well defined sentence. The only way to ensure that one's arrival does not occur prior to one's departure is to not travel FTL. Otherwise due to relativity, your arrival is guaranteed to be prior to your departure in some frame. As discussed at length in this thread, all inertial frames are equivalent, so you can't say one frame is the one to determine order of events in without throwing out relativity.

[giulioprisco]

I think an imaginative but scientifically sound way to look at the possibility of FTL can start with realizing that empty space (the vacuum) can be usefully thought of a superconducting/superfluid material. This isn't controversial but mainstream physics (ref. Wilczek, Volovik...).

Slightly more imaginative is the idea that our physics is really the physics of quasiparticles in a "trans-Planckian" medium (ref. Volovik's The Universe in a Helium Droplet). So the particles and fields that we see are something like phonons, excitation of a more fundamental underlying substrate that we don't see.

Einstein's metric itself could an be emergent property of the substrate. In condensed materials, quasiparticles move with a maximum speed determined by an effective spacetime metric. This maximum speed is much less than the speed of light in vacuum.

Similarly, the maximum speed in the underlying "real world" from which our particles and fields emerge as quasiparticle-like excitations could be much higher than our speed of light in vacuum.

[KelvinZero]

This thread is not specifically about the possibility of FTL and certainly not about any particular theory.
Any valid theory would at least deserve it's own thread.

This thread is about how the very famous paradoxes could be avoided. For example, it probably has to explain how simultaneous could even be defined between distant points in space.

[ChrisWilson68]

I think an imaginative but scientifically sound way to look at the possibility of FTL can start with realizing that empty space (the vacuum) can be usefully thought of a superconducting/superfluid material. This isn't controversial but mainstream physics (ref. Wilczek, Volovik...).

Slightly more imaginative is the idea that our physics is really the physics of quasiparticles in a "trans-Planckian" medium (ref. Volovik's The Universe in a Helium Droplet). So the particles and fields that we see are something like phonons, excitation of a more fundamental underlying substrate that we don't see.

Einstein's metric itself could an be emergent property of the substrate. In condensed materials, quasiparticles move with a maximum speed determined by an effective spacetime metric. This maximum speed is much less than the speed of light in vacuum.

Similarly, the maximum speed in the underlying "real world" from which our particles and fields emerge as quasiparticle-like excitations could be much higher than our speed of light in vacuum.

That is basically what people thought in the 19th Century -- that there was a substrate and light was moving in that substrate.  If that's the case, it should be possible to detect which frame of reference the substrate is in -- i.e. it's movement relative to the Earth.  The Michelson-Morley experiment, among others, tried to detect such movement relative to a substrate.  The failure of such experiments to get results consistent with a substrate led to the development of relativity, which explains experimental data much better than any substrate theory.

[WarpTech]

I think an imaginative but scientifically sound way to look at the possibility of FTL can start with realizing that empty space (the vacuum) can be usefully thought of a superconducting/superfluid material. This isn't controversial but mainstream physics (ref. Wilczek, Volovik...).

Slightly more imaginative is the idea that our physics is really the physics of quasiparticles in a "trans-Planckian" medium (ref. Volovik's The Universe in a Helium Droplet). So the particles and fields that we see are something like phonons, excitation of a more fundamental underlying substrate that we don't see.

Einstein's metric itself could an be emergent property of the substrate. In condensed materials, quasiparticles move with a maximum speed determined by an effective spacetime metric. This maximum speed is much less than the speed of light in vacuum.

Similarly, the maximum speed in the underlying "real world" from which our particles and fields emerge as quasiparticle-like excitations could be much higher than our speed of light in vacuum.

That is basically what people thought in the 19th Century -- that there was a substrate and light was moving in that substrate.  If that's the case, it should be possible to detect which frame of reference the substrate is in -- i.e. it's movement relative to the Earth.  The Michelson-Morley experiment, among others, tried to detect such movement relative to a substrate.  The failure of such experiments to get results consistent with a substrate led to the development of relativity, which explains experimental data much better than any substrate theory.

Not so fast. Today's quantum field theory is just that, there is a "field" which can only be observed by the "particle excitations" of the field. The field is not the sum of the particles, the particles are the excitations of the field and may be created or annihilated at any time. The field is the "substrate" as you put it, but is unobservable if not for its particle excitations.

Take the EM Zero Point Field for example. Motion relative to the ZPF, (i.e., any EM spectral energy density proportional to frequency³) is unobservable. Yet we can observe it in the Casimir effect and the Lamb shift. More importantly, uniform-changes in the spectral energy density of the EM ZPF are equally unobservable.

Point being, regarding the statement; "If that's the case, it should be possible to detect which frame of reference the substrate is in --" is an assumption that has been proven false by the existence of a ZPF and QFT in general.

[ChrisWilson68]

I think an imaginative but scientifically sound way to look at the possibility of FTL can start with realizing that empty space (the vacuum) can be usefully thought of a superconducting/superfluid material. This isn't controversial but mainstream physics (ref. Wilczek, Volovik...).

Slightly more imaginative is the idea that our physics is really the physics of quasiparticles in a "trans-Planckian" medium (ref. Volovik's The Universe in a Helium Droplet). So the particles and fields that we see are something like phonons, excitation of a more fundamental underlying substrate that we don't see.

Einstein's metric itself could an be emergent property of the substrate. In condensed materials, quasiparticles move with a maximum speed determined by an effective spacetime metric. This maximum speed is much less than the speed of light in vacuum.

Similarly, the maximum speed in the underlying "real world" from which our particles and fields emerge as quasiparticle-like excitations could be much higher than our speed of light in vacuum.

That is basically what people thought in the 19th Century -- that there was a substrate and light was moving in that substrate.  If that's the case, it should be possible to detect which frame of reference the substrate is in -- i.e. it's movement relative to the Earth.  The Michelson-Morley experiment, among others, tried to detect such movement relative to a substrate.  The failure of such experiments to get results consistent with a substrate led to the development of relativity, which explains experimental data much better than any substrate theory.

Not so fast. Today's quantum field theory is just that, there is a "field" which can only be observed by the "particle excitations" of the field. The field is not the sum of the particles, the particles are the excitations of the field and may be created or annihilated at any time. The field is the "substrate" as you put it, but is unobservable if not for its particle excitations.

Take the EM Zero Point Field for example. Motion relative to the ZPF, (i.e., any EM spectral energy density proportional to frequency³) is unobservable. Yet we can observe it in the Casimir effect and the Lamb shift. More importantly, uniform-changes in the spectral energy density of the EM ZPF are equally unobservable.

Point being, regarding the statement; "If that's the case, it should be possible to detect which frame of reference the substrate is in --" is an assumption that has been proven false by the existence of a ZPF and QFT in general.

A field is not a "substrate" in the sense that the original poster was talking about -- something that could give a slower speed of light in the substrate than the speed of light in a true vacuum.

If it can give light a different speed, it has a frame of reference associated with it, unless you want to toss all of known physics and come up with a completely new theory.

[KelvinZero]

The topic on this thread is just how paradoxes are resolved though.

So for example, in this case all I want to know is if the paradoxes are being resolved by limiting FTL to be with respect to a special frame. If so then what is that frame. If not, then how do you resolve the paradoxes, how do you define "instantaneous" between two events?

The explanation has to make sense without being a physicist. You can't sell FTL to a tourist with the slogan "buy this trip to alpha centauri. The outcome is indescribable".



IMO we have one ok resolution using a special frame. (instantaneous FTL travel is between points of the same CMB temperature). I don't think this actually breaks relativity. It does not require any current test to stop working that i am aware of. I totally accept that it is like sewing a 5th leg on your racehorse and no reason has been presented of why you should do so. Im only concerned with paradoxes and if you can actually describe what you mean when you say FTL. Otherwise you might as well replace "FTL" with "Smurf", and produce detailed mathematics to prove you can smurf your smurf.

[laszlo]

You say above that this thread is not about the possibility of FTL, and that the topic is how paradoxes are resolved and it has to make sense without being a physicist. Sounds like you can have any two out of three.

The easiest way to resolve a paradox is to avoid it in the first place i.e., admit that FTL is impossible. Resolved and no physics degree needed.

Adding epicycles and aether and throwing away Occam's razor requires the intended audience to be able to understand why those things are necessary even though they make no sense. That requires math and a good knowledge of real physics, i.e., a physicist.

You've set yourself an impossible task that will accomplish nothing. Just posit that the same space-fairy magic that makes FTL possible takes care of the paradoxes and move on with your life. Surely you have something better to do.

[WarpTech]

That is basically what people thought in the 19th Century -- that there was a substrate and light was moving in that substrate.  If that's the case, it should be possible to detect which frame of reference the substrate is in -- i.e. it's movement relative to the Earth.  The Michelson-Morley experiment, among others, tried to detect such movement relative to a substrate.  The failure of such experiments to get results consistent with a substrate led to the development of relativity, which explains experimental data much better than any substrate theory.

Not so fast. Today's quantum field theory is just that, there is a "field" which can only be observed by the "particle excitations" of the field. The field is not the sum of the particles, the particles are the excitations of the field and may be created or annihilated at any time. The field is the "substrate" as you put it, but is unobservable if not for its particle excitations.

Take the EM Zero Point Field for example. Motion relative to the ZPF, (i.e., any EM spectral energy density proportional to frequency³) is unobservable. Yet we can observe it in the Casimir effect and the Lamb shift. More importantly, uniform-changes in the spectral energy density of the EM ZPF are equally unobservable.

Point being, regarding the statement; "If that's the case, it should be possible to detect which frame of reference the substrate is in --" is an assumption that has been proven false by the existence of a ZPF and QFT in general.

A field is not a "substrate" in the sense that the original poster was talking about -- something that could give a slower speed of light in the substrate than the speed of light in a true vacuum.

If it can give light a different speed, it has a frame of reference associated with it, unless you want to toss all of known physics and come up with a completely new theory.

Your statement is not well defined. In a Schwarzschild metric background for instance, in any "local" approximation of an inertial reference frame, c = c, is a constant. But take any one of those inertial frames, such as the one of a very distant observer, and from his perspective, the coordinate speed of light is a function of radial distance from the CoM.

c(r) = c*(1 - 2GM/rc^2)

In GR, the coordinate speed of light is not a constant, but in any local approximation of an inertial frame, it is. So your statement; "If it can give light a different speed, it has a frame of reference associated with it, unless you want to toss all of known physics and come up with a completely new theory.", is once again an assumption that is refuted by GR and also by the Polarizable Vacuum Model of GR, which show we can have it both ways, and it doesn't require us to toss out anything.

You assume c is constant in the local inertial frame, GR shows the coordinate speed c(r) is not constant, when viewed from a distant inertial frame. In one frame, it is obvious that c(r) is a variable with distance, but like a fish that doesn't know he's in the water, in the local frame, that change in c can't be measured or observed.

[meberbs]

You assume c is constant in the local inertial frame, GR shows the coordinate speed c(r) is not constant, when viewed from a distant inertial frame. In one frame, it is obvious that c(r) is a variable with distance, but like a fish that doesn't know he's in the water, in the local frame, that change in c can't be measured or observed.

The relevant speed he is discussing clearly seems to be the proper speed, not the coordinate speed.

[KelvinZero]

You say above that this thread is not about the possibility of FTL, and that the topic is how paradoxes are resolved and it has to make sense without being a physicist. Sounds like you can have any two out of three.

No I don't think so. Let me explain again.

The reason I have been very clear that the answer must make sense without being a physicist is because several replies were of the form: "There is no paradox because <insert jargon>". This is of no use because you have to be able explain what someone actually experiences if they attempt to implement one of the standard paradoxes. Obviously, someone who takes an FTL trip has to experience a set of events even if they are not a physicist.

Currently we have one candidate for resolving paradoxes I consider "good enough for science fiction". I repeat, It is not about being true, just about being describable.

One way you could contribute is coming up with other candidates of resolutions to paradoxes, that do not require tests we have already done to start returning different results.

Another way you could contribute is by producing clear examples of how physics would break even assuming this candidate, and begin producing nonsensical, paradoxical claims.

My hope, as an outcome for this entire thread, is that if any other thread starts to discuss some particular FTL proposal, we will be able to get the proponent to at least clarify what they mean by FTL, by placing it in one of these categories.

[WarpTech]

You assume c is constant in the local inertial frame, GR shows the coordinate speed c(r) is not constant, when viewed from a distant inertial frame. In one frame, it is obvious that c(r) is a variable with distance, but like a fish that doesn't know he's in the water, in the local frame, that change in c can't be measured or observed.

The relevant speed he is discussing clearly seems to be the proper speed, not the coordinate speed.

The original poster specifically said;

...
Einstein's metric itself could an be emergent property of the substrate. In condensed materials, quasiparticles move with a maximum speed determined by an effective spacetime metric. This maximum speed is much less than the speed of light in vacuum.

That is what I just said about c(r), the coordinate speed of light is determined by the "spacetime metric". He wasn't referring to the "proper speed".

[meberbs]

...
Einstein's metric itself could an be emergent property of the substrate. In condensed materials, quasiparticles move with a maximum speed determined by an effective spacetime metric. This maximum speed is much less than the speed of light in vacuum.

That is what I just said about c(r), the coordinate speed of light is determined by the "spacetime metric". He wasn't referring to the "proper speed".

He was talking about speed of light relative to a (local) substrate. The relevant speed is the proper speed not the coordinate speed. You know what proper speed means right? The way you put it in quotes while not putting coordinate speed in quotes makes me think that you think I just made up the term.

[Elrond Cupboard]

Here's something, that has been exercising my mind a little of late; from an outsider with, probably, enough physics to be dangerous.

GR seems to tell me that any event in the future in my inertial frame, lies in the past for an infinite number of other frames.

Where does that leave free will?

[meberbs]

Here's something, that has been exercising my mind a little of late; from an outsider with, probably, enough physics to be dangerous.

GR seems to tell me that any event in the future in my inertial frame, lies in the past for an infinite number of other frames.

Where does that leave free will?

There is a defined future and past for you, your "future light cone" and "past light cone" The future consists of all events you can effect and the past of all events that can effect you. There are also events that are neither "spacelike separated events" are ones that are indeterminate whether they are in your future or past, so they cannot affect or be affected by your current state. None of this directly prevents free will.

As for free will, most of physics is deterministic, which means no free will. With quantum mechanics, some interpretations are not deterministic, which means quantum explicitly has a loophole for freewill. (There are both deterministic and non-deterministic interpretations, but someone found a way to test a certain class of deterministic interpretations and they have been found to not hold. As a result, many physicists have been resigned to accept the non-deterministic interpretation, since the remaining deterministic ones are unattractive. This doesn't matter though since as far as we know there is no way to tell them apart.)

[Elrond Cupboard]

Here's something, that has been exercising my mind a little of late; from an outsider with, probably, enough physics to be dangerous.

GR seems to tell me that any event in the future in my inertial frame, lies in the past for an infinite number of other frames.

Where does that leave free will?

There is a defined future and past for you, your "future light cone" and "past light cone" The future consists of all events you can effect and the past of all events that can effect you. There are also events that are neither "spacelike separated events" are ones that are indeterminate whether they are in your future or past, so they cannot affect or be affected by your current state. None of this directly prevents free will.

As for free will, most of physics is deterministic, which means no free will. With quantum mechanics, some interpretations are not deterministic, which means quantum explicitly has a loophole for freewill. (There are both deterministic and non-deterministic interpretations, but someone found a way to test a certain class of deterministic interpretations and they have been found to not hold. As a result, many physicists have been resigned to accept the non-deterministic interpretation, since the remaining deterministic ones are unattractive. This doesn't matter though since as far as we know there is no way to tell them apart.)

Thank you for your thoughtful reply; it doesn't quite address the question I attempted to pose. I shall return when I have reformulated it.

[RSE]

Kelvinzero, here is a response for a hard science fictional viewpoint. There is no way to have FTL drive without causing paradoxes in SR and GR. However, the complete answer is not so simple.

First there are two question tied together in the simple term FTL. One must first separate them, as they are not identical.  They are 1.) traveling faster that light itself. And 2.) traveling faster that c. Those question are not the same.

Question #1. - Traveling faster than light itself. We have no data or testable theory to work with. The only thing we would have is that whatever new theory and/or data would have to reduce to GR and SR at sub-light speeds; the same concept that SR and GR reduce to Newtonian mechanics at very slow speeds.

Question #2. - Traveling faster than c. Here we have theory and testable methodologies to work with. To forestall the back-and-forth, I will describe them here. C, (the speed of light in a vacuum), has been tested an enormous number of times, with a consistent result. This is granted. The question is not what is c , but why is c? For theory on that, one has to go back before GR and SR, to Maxwell's Equations. More particularly, to the boundary requirements of Maxwell's Equations. The second boundary condition defines c as 1 /square root of (the permittivity of a vacuum * the permeability of a vacuum).

This was a major bone of contention for SR when it was published. The issue was finally settled by 1915, with the viewpoint that there was no way to change those aspects of a vacuum, therefore it was a moot point. The result was that c became canonical to physics.

However, in the late 1990's, ways were discovered to alter Permittivity and Permeability, initially to create materials that had both negative Permittivity and Permeability, which should cause a number of bizarre effects. Most (but not all) of these have been tested, and in every tested case proved to be actual. For brevity, I will leave most of them out, but mention only 2. The first, was that due to certain quantum related aspects to light, which are imaginary under positive Permittivity and Permeability conditions, became real under negative conditions, which allows items less than the length of the a wavelength of light, to be visualized by that wavelength. The second, and much more relevant, was the first boundary condition of Maxwell's Equations, which says that the wave propagation in a positive material propagates in the same direction as the photon is travelling in. In a negative material, it should propagate in the opposite direction. Experiments have shown that this is the case with negative  Permittivity and Permeability materials.

Which leads to the question #2 above. If you made a field with lower Permittivity and Permeability than a vacuum, what is the speed of light under that field? C, or the value that Maxwell's second boundary condition would calculate? If it is the latter, there is the theory for a faster than c drive. Same equations as GR and SR, only with c as a variable. (Of course, no theory on the interrelation between different frames with different valid values of c. The paradoxes would have to be solved by that new theory.) When you set c to the standard permittivity and pearmeability value of the universe, it reduces to GR and SR.

To reduce this for a “hard SF” FTL drive, I leave to the SF writer. . .

[WarpTech]

Kelvinzero, here is a response for a hard science fictional viewpoint. There is no way to have FTL drive without causing paradoxes in SR and GR. However, the complete answer is not so simple.

First there are two question tied together in the simple term FTL. One must first separate them, as they are not identical.  They are 1.) traveling faster that light itself. And 2.) traveling faster that c. Those question are not the same.

Question #1. - Traveling faster than light itself. We have no data or testable theory to work with. The only thing we would have is that whatever new theory and/or data would have to reduce to GR and SR at sub-light speeds; the same concept that SR and GR reduce to Newtonian mechanics at very slow speeds.

Question #2. - Traveling faster than c. Here we have theory and testable methodologies to work with. To forestall the back-and-forth, I will describe them here. C, (the speed of light in a vacuum), has been tested an enormous number of times, with a consistent result. This is granted. The question is not what is c , but why is c? For theory on that, one has to go back before GR and SR, to Maxwell's Equations. More particularly, to the boundary requirements of Maxwell's Equations. The second boundary condition defines c as 1 /square root of (the permittivity of a vacuum * the permeability of a vacuum).

This was a major bone of contention for SR when it was published. The issue was finally settled by 1915, with the viewpoint that there was no way to change those aspects of a vacuum, therefore it was a moot point. The result was that c became canonical to physics.

However, in the late 1990's, ways were discovered to alter Permittivity and Permeability, initially to create materials that had both negative Permittivity and Permeability, which should cause a number of bizarre effects. Most (but not all) of these have been tested, and in every tested case proved to be actual. For brevity, I will leave most of them out, but mention only 2. The first, was that due to certain quantum related aspects to light, which are imaginary under positive Permittivity and Permeability conditions, became real under negative conditions, which allows items less than the length of the a wavelength of light, to be visualized by that wavelength. The second, and much more relevant, was the first boundary condition of Maxwell's Equations, which says that the wave propagation in a positive material propagates in the same direction as the photon is travelling in. In a negative material, it should propagate in the opposite direction. Experiments have shown that this is the case with negative  Permittivity and Permeability materials.

Which leads to the question #2 above. If you made a field with lower Permittivity and Permeability than a vacuum, what is the speed of light under that field? C, or the value that Maxwell's second boundary condition would calculate? If it is the latter, there is the theory for a faster than c drive. Same equations as GR and SR, only with c as a variable. (Of course, no theory on the interrelation between different frames with different valid values of c. The paradoxes would have to be solved by that new theory.) When you set c to the standard permittivity and pearmeability value of the universe, it reduces to GR and SR.

To reduce this for a “hard SF” FTL drive, I leave to the SF writer. . .

You just described the Polarizable Vacuum Model of General Relativity, which was first considered by Dicke, and later by Putoff and myself.

http://forum.nasaspaceflight.com/index.php?topic=40959.msg1583932#msg1583932