Looking for new physics via twins, one way speed of light and galaxy rotation

[Killtech]

It is known that the one way speed of light cannot be measured under normal circumstance, however there are a few special interesting cases. Let's consider the situation of the twin paraoxon, except we assume the world is shaped like a cylinder thus having a finite length in one direction. In this unique settings we can still discuss the twin paradox within special relativity where the two twins travel exclusively in inertial frames, yet are able to periodically meet each other since geodesics around the circumference of the cylinder form closed loops. These meetings allow to make age comparisons locally and logic requires that there must be a uniquely determined, frame independent answer which twin is older. So globally inertial frames are not strictly equivalent in such a case and indeed there can only exist one frame where aging will happen the fastest.

In the same situation each twin could also send two light signals (instead of his twins) in opposed directions around the circumference, wait for their return and determine the delay between them. This delay is the difference in the one way speed of light along those two directions. There is only one frame where both signals arrive simultaneously and which is also the same where clock tick the fastest. So we have a case in SR where a preferred frame exists that acts a bit as absolute rest frame. 

This is a pure theoretical scenario since we have no experimental indication for a topology with nontrivial homotopy class (i think). But I was contemplating if we can make use of these considerations in a normal situation. After all we still can send light along closed loops in two directions and determine the delay, for example along a planet's orbit. But i figured that will merely measure which angular velocity the light ring has.

In general, if we consider the difference in the one way speed of light to be a vector field, we find that a closed loop only measures its average difference along the loops tangent vector, hence it will always yield a 0 result for constant or conservative vector fields. But if the field has a curl, it will not.

So... what would happen if we place such a light-signal ring along the outer rim of a galaxy? It is an open issue that our current physical models find the observed galaxy rotation curve to be quite abnormal. Is it thinkable that the angular velocity obtained from observing the delay in light signals measured by the ring will differ from the velocity obtained by other means? This is another approach to Mach's question of absolute rotation. Because the possibility of a curl in the one way speed of light could be practically considered as space itself being partially dragged along a rotating object, therefore the object will perceive a lower angular momentum then a distant observer would visually assume. Such an additional degree of freedom would allow a galaxy to match the modelled angular momentum curve and with the angular velocity of space added on top still obtain the observed behavior.

This is of course pure hypothetical/speculative, but the question whether that makes sense to look for experimentally is not. finding things that may be of interest for measurement is always looking for possibilities beyond the established - hence why i posted this here rather then the speculation forum section. As far as i understand GR, it isn't able to account such a possibility as that would at least require to introduce a torsion degree of freedom to its connection - thus this is looking for new physics. I don't know of any experiments that would have discounted such a possibility already, or does someone know any?

[Halc]

1 hour ago, Killtech said:

Let's consider the situation of the twin paraoxon, except we assume the world is shaped like a cylinder thus having a finite length in one direction. In this unique settings we can still discuss the twin paradox within special relativity where the two twins travel exclusively in inertial frames

You're talking about flat spacetime that wraps in one dimension, sort of like Pacman game. Yes, One can do SR exercises in that, eliminating say acceleration necessity, but at the cost of having a preferred orientation of axes and also a preferred frame, a violation of the first premise. 

So you, at Earth, see a line of Earths in opposite directions but none of the others. You can travel to one of them and compare clocks when you get there. It's the same Earth after all. Or Earth can travel to you.

1 hour ago, Killtech said:

These meetings allow to make age comparisons locally and logic requires that there must be a uniquely determined, frame independent answer which twin is older.

You already have that with normal spacetime (infinite in all directions). The difference in age between the twins when they reunite is a physical fact, meaning it isn't in any way frame dependent.

1 hour ago, Killtech said:

In the same situation each twin could also send two light signals (instead of his twins) in opposed directions around the circumference, wait for their return and determine the delay between them. This delay is the difference in the one way speed of light along those two directions.

And in so doing, they have a test for being stationary in the preferred frame. You seem to realize this because yes, the one-way speed of light can now be measured.

1 hour ago, Killtech said:

So we have a case in SR where a preferred frame exists that acts a bit as absolute rest frame. 

Given the wrapping geometry you describe, absolutely, yes.

1 hour ago, Killtech said:

After all we still can send light along closed loops in two directions and determine the delay, for example along a planet's orbit.

Sounds like a Sagnac effect which yes, can be used to detect rotation. Thus rotation is absolute.

1 hour ago, Killtech said:

So... what would happen if we place such a light-signal ring along the outer rim of a galaxy? It is an open issue that our current physical models find the observed galaxy rotation curve to be quite abnormal. Is it thinkable that the angular velocity obtained from observing the delay in light signals measured by the ring will differ from the velocity obtained by other means? This is another approach to Mach's question of absolute rotation. Because the possibility of a curl in the one way speed of light could be practically considered as space itself being partially dragged along a rotating object, therefore the object will perceive a lower angular momentum then a distant observer would visually assume. Such an additional degree of freedom would allow a galaxy to match the modelled angular momentum curve and with the angular velocity of space added on top still obtain the observed behavior.

I cannot follow this. Yes, there is frame dragging, but it isn't going to be measured at such low gravitational gradients such as exist at the edge of a galaxy.  You have a ring, implemented with say a number of mirrors to keep the refractive index at 1. What experimental result are you expecting here?  Is the ring rotating with the galaxy?  Is this just a huge-scale Sagnac rotation sensor?  What at all does this have to do with your wrapping SR example. As soon as you introduced a galactic mass and dark matter and such, SR no longer applies.

[Killtech]

1 hour ago, Halc said:

I cannot follow this. Yes, there is frame dragging, but it isn't going to be measured at such low gravitational gradients such as exist at the edge of a galaxy.  You have a ring, implemented with say a number of mirrors to keep the refractive index at 1. What experimental result are you expecting here?  Is the ring rotating with the galaxy?  Is this just a huge-scale Sagnac rotation sensor?  What at all does this have to do with your wrapping SR example. As soon as you introduced a galactic mass and dark matter and such, SR no longer applies.

Yes, the gedankenexperiment is to place a Sagnac sensor (thanks for the proper name) moving along a galaxies disk (i.e. no relative rotation) and use it to measure the angular velocity at that radius to compare it with usual methods of determining a galaxies rotation curve from afar. Our current physical model would expect these methods yield agreeing results. However, i suggest to test if this assumption holds in such circumstance. 

For example one possible outcome could be that the Sagnac interferometer would yield an angular velocity close to our current model of gravity without the presence of dark matter, which is much lower to what the outside observer measures. The idea is merely based on the cylinder case where also a Sagnac test is used to determine the difference in the one way speed of light. I only mentioned SR because it allows to study this surprising case and its implications - particularly the concept of a preferred frame in relativity.

Maybe consider doing a similar experiment in other area of physics to understand the motivation better: Let's take a miniature plastic model of a galaxy and let it spin under water (or better, a superfluid). The spinning galaxy will also cause the surrounding medium to partially flow along the rotation in a curl flow, a vortex will form. We conduct an analoge of a Sagnac sensor but instead of using light, we use acoustic signals which propagate via the medium. Calculating the delay between the signals works similar to light except that the medium defines the one way speed of sound along the signals path. In this case the sensor therefore only measure the angular velocity of the galaxy relative to the rotating medium around it. Because of this the measured result will deviate from the actual angular velocity observed from afar.

[Halc]

3 hours ago, Killtech said:

Yes, the gedankenexperiment is to place a Sagnac sensor (thanks for the proper name) moving along a galaxies disk (i.e. no relative rotation) and use it to measure the angular velocity at that radius to compare it with usual methods of determining a galaxies rotation curve from afar. Our current physical model would expect these methods yield agreeing results.

Well, it would match the 'usual methods' only if the clock at the 'afar' place was a similar gravitational potential relative to the clock measuring the trip around the ring.

3 hours ago, Killtech said:

For example one possible outcome could be that the Sagnac interferometer would yield an angular velocity close to our current model of gravity without the presence of dark matter, which is much lower to what the outside observer measures.

Would it now? That seems to violate your stipulation that the ring rotates at the same angular velocity as the material local to it. Maybe you imply that the Sagnac device would somehow not work correctly in this situation. Would the sum of the two signal times still be the same as the non-rotating case, which is basically πD/c ?

Also, an interferometer measures femptosecond differences and would be pretty inappropriate for measuring the ~4 month difference in the signals going each way.  How about we use a calendar instead?

3 hours ago, Killtech said:

Let's take a miniature plastic model of a galaxy and let it spin under water (or better, a superfluid). The spinning galaxy will also cause the surrounding medium to partially flow along the rotation in a curl flow, a vortex will form. We conduct an analoge of a Sagnac sensor but instead of using light, we use acoustic signals which propagate via the medium. Calculating the delay between the signals works similar to light except that the medium defines the one way speed of sound along the signals path. In this case the sensor therefore only measure the angular velocity of the galaxy relative to the rotating medium around it. Because of this the measured result will deviate from the actual angular velocity observed from afar.

A superfluid wouldn't move with the spinning thingy, but a regular fluid would, and energy input would be needed to keep it spinning.

OK, so you measure the rate at which the fluid rotates by somehow confining sound to a ring of the stuff. Clue: Ditch the plastic galaxy and instead spin a hula-hoop with fluid in it. You can put your sonic rotation sensor in there, and measure if the fluid rotates at the same rate as the hoop, slower, faster, backwards, or not at all. With light, relativity predicts numbers corresponding to no rotation of the 'medium' at all, regardless of where the ring is going or how fast it spins. You can speculate some different answer, but absent an actual experiment, what's the point except denialism?

What does any of this have to do with the presence of dark matter or not. It's just more matter which is hard to see or feel directly. It isn't anything magical, and this experiment seems to be an attempt at a aether detector, not relevant in any way to the existence of dark matter or not.

[Killtech]

7 minutes ago, Halc said:

Also, an interferometer measures femptosecond differences and would be pretty inappropriate for measuring the ~4 month difference in the signals going each way.  How about we use a calendar instead?

fair enough, bad wording. an interferometer for the purpose would have use a pretty extreme wavelength.

7 minutes ago, Halc said:

A superfluid wouldn't move with the spinning thingy, but a regular fluid would, and energy input would be needed to keep it spinning.

in my mind the plastic model of a spiral galaxy was shaped more like an airscrew. but fair enough, a perfect flat disc wouldn't be able to move a medium without friction. you got the point anyway. 

7 minutes ago, Halc said:

OK, so you measure the rate at which the fluid rotates by somehow confining sound to a ring of the stuff. Clue: Ditch the plastic galaxy and instead spin a hula-hoop with fluid in it. You can put your sonic rotation sensor in there, and measure if the fluid rotates at the same rate as the hoop, slower, faster, backwards, or not at all. With light, relativity predicts numbers corresponding to no rotation of the 'medium' at all, regardless of where the ring is going or how fast it spins. You can speculate some different answer, but absent an actual experiment, what's the point except denialism?

I know the prediction GR makes. But i also I don't know any kind of experiments which would already reliably disprove this possibility, though i may be wrong - so correct me if i am. For this scenario the theory does not seem to be well tested and its predictions are therefore in an extrapolating regime. But of course that does not disprove it in any way.

As i stated in my opening post, the purpose is to formulate/sketch the idea for an experiment that might be looking for physics beyond the currently known. After all the purpose of experiments is to test a theory - and that's especially interesting for things it hasn't been tested for.

7 minutes ago, Halc said:

What does any of this have to do with the presence of dark matter or not. It's just more matter which is hard to see or feel directly. It isn't anything magical, and this experiment seems to be an attempt at a aether detector, not relevant in any way to the existence of dark matter or not.

well, look up the galaxy rotation curve issue which shows a big discrepancy between model if we only consider the visible matter. The introduction of large quantities of dark matter outside the galaxy is the preferred hypothesis to mend the discrepancy between the model and the observation. MOND is another approach. however, both are merely assumptions, neither is considered experimentally established.

A rotating aether or equivalently introducing torsion degrees of freedom to the affine connection GR uses might be another alternative.

Anyhow, the issue is that a galaxy spanning ring is not particularly ideal to build for an experiment - yet this is the case where the discrepancies with observation are the largest. Is there a better way to test such a hypothesis?

 

[Halc]

19 hours ago, Killtech said:

But i also I don't know any kind of experiments which would already reliably disprove this possibility, though i may be wrong - so correct me if i am.

There seems to be no actual theory behind your idea, so no quantifiable prediction. What problem does it solve? If it doesn't solve one, and it also contractions the last century of physics, and the only experiment you envision is one that is wildly unfeasible, then there's really no point in it all, is there? I mean, I could posit that pink elephants only on some planet 100 LY away can locomote around with reactionless thrust. Why haven't we tested that idea? Or we can posit that physics is the same everywhere except for humans, all without evidence. OK, that last one is real, but funny that it would be so easy to verify, and yet no attempt is made.

[Killtech]

23 hours ago, Halc said:

There seems to be no actual theory behind your idea, so no quantifiable prediction. What problem does it solve?

I have written that a few times, but you are seem keen on jumping over it. the problem is the galaxy rotation curves as indicated by the mass-to-light ratios anomalies since we have no solution to this problem. If you cite dark matter as a solution, then note how that hypothesis works: given a deep mismatch between the GR model and observation we introduce a completely unknown field-like degree of freedom to GR, just so generic and flexible that it can fit almost any deviation. But that flexibility renders it no actual quantifiable theory but free empiric parameters that must be fit experimentally. And experimentally, our means are not good enough to do even that to a satisfactory degree. Sure there have been a lot of proposals to what dark matter may be in order to somewhat constrain these parameters but let's be honest, so far we haven't come far understanding it at all.

Adding torsion to GR is just another alternative to fix the same problem and it is a hypothesis similarly generic to dark matter with its own degrees of freedom, meaning it opens up a large class of possible models with wider range of predictions - same as dark matter does. And since the concept is similarly flexible, it can potentially make most of the dark matter obsolete.

Unless you consider the question of dark matter resolved and well understood, there is still a big problem to solve. 

23 hours ago, Halc said:

it also contractions the last century of physics, and the only experiment you envision is one that is wildly unfeasible, then there's really no point in it all, is there?

Look how much we try to learn about dark matter from simulations. For these the concept is very feasible - albeit admittedly just as satisfactory as the dark matter explanation. 

In terms of actual observations i was thinking that one could potentially try to do a Segnac experiment in a much smaller system, like around earths orbit via satelites. But of course here the effect might be much less prominent and thus harder to detect.