[Kryptid]

But instant action at a distance is certainly the standard modern explanation

No it isn't. I think you might be confusing gravitational fields with quantum entanglement.

[mad aetherist (OP)]

Ok i found some good articles explaining how LIGO works.

LIGO reckon that a gravity wave (1) can change the length tween mirrors in their two 4 km legs (set at 90 deg).........
Comment -- They say that (1a)  the length of the 4 km pipelines dont change (because GWs dont affect the dimensions of solid objects) -- but that (1b) the length 4 km tween end mirrors does change because the end mirrors are in effect in free-fall as regards length (& (1c) GWs do affect the dimensions of space).
..... & at the same time the gravity wave will (2) change the wavelength of the laser light (used to give an interference fringe) by the same amount.....
Comment -- Yes & no -- (2a) yes, initially when the GW first arrives the wavelength changes by the same amount as the distance tween mirrors -- (2b) & no, once the initial load of light waves exits the leg, the new waves will (for a long while) have the same wavelength as before the GW arrived.

......... but (3) that a gravity wave cannot change the speed of the laser light in any leg at any time.......
Comment -- yes thats what they say.

............. (4) hencely giving a fringeshift (if the change in length in each leg is non-equal).
Comment -- (4a) yes thats what they say -- the time in the stretched leg is longer than the time in the compressed leg, (4b) & this manifests as a fixed constant fringeshift, (4c) except that the GW is continually changing strength & hencely (4d) the fringeshift changes accordingly hencely (4e) a chirp.

This looks silly.
Do they think that (5) a GW can change length, ie space, but cannot change time?
Or do they look at it in a different way -- eg do they think (6) that a GW can change length in spacetime but cannot change time in spacetime?

According to (2) the number of light waves in each leg always stays exactly the same (except for unwanted noise)
Comment -- No thats not what they say -- they say that the number of waves in each leg changes.
& according to (3) the light speed in each leg stays the same (= c), so i dont see how there could be a fringeshift in (4).  (7) I dont see a fringeshift, i see a paradox.  What exactly is their logic?
Comment -- No their reasoning if correct would result in a fringeshift as claimed.

[mad aetherist (OP)]

Here is a good article & link re LIGOs fringeshifts.

If light waves are stretched by gravitational waves, how can we use light as a ruler to detect gravitational waves?
Peter R. Saulson Department of Physics, Syracuse University, Syracuse, New York
https://pdfs.semanticscholar.org/393a/af6b1ced305ee40d175d5f3c3a2b6020348d.pdf

[Bored chemist]

"If light waves are stretched by gravitational waves, how can we use light as a ruler to detect gravitational waves?"
By comparing it to light that traveled at right angles to the wave and thus was not stretched out.


Was that somehow meant to be a difficult question?

[mad aetherist (OP)]

"If light waves are stretched by gravitational waves, how can we use light as a ruler to detect gravitational waves?"
By comparing it to light that traveled at right angles to the wave and thus was not stretched out.
Was that somehow meant to be a difficult question?

The inference was the same inference as in my #1 posting -- that if light waves are stretched & if the 4 km leg is stretched likewise then how can u get a fringeshift.
In an MMX this happens too, but in an MMX u have a 2nd order slowing of light in one of the 2 legs & thusly get a small fringeshift -- but in LIGO there is no such 2nd order slowing -- so the question arises.
LIGO try to get out of this problem by saying that even tho the speed of light is not changed that the wavelength of light is (eventually) the same as the initial wavelength -- & hencely LIGO sees a fringeshift (koz the L tween mirrors changes).
In an MMX the length of a leg changes due to the change in aetherwind & gamma -- in LIGO a GW doesnt change the length of a leg (ie the length of the pipeline itself), but they say a GW does change the distance tween hanging mirrors (as if the mirrors were in free-fall)(even tho they are only hanging)(ie fixed vertically but not fixed horizontally).
The main difference tween an MMX & LIGO is that in an MMX the wavelength is affected by gamma -- but in LIGO there is no gamma to change the wavelength, & re the GW they say that a GW cant change wavelength (except in the early part of the GW, but not in the main later part of the GW).

Here is a part of my #1 posting.
LIGO reckon that a gravity wave (1) can change the length tween mirrors in their two 4 km legs (set at 90 deg) -- & at the same time the gravity wave will (2) change the wavelength of the laser light (used to give an interference fringe) by the same amount -- but (3) that a gravity wave cannot change the speed of the laser light in any leg at any time -- (4) hencely giving a fringeshift (if the change in length in each leg is non-equal).