Your first statement is wrong:

AS: 1. LIGO did not observe directly the interference pattern which is computer simulation.

The published results include both the actual output of the interferometer expressed as the measured strain and separately the waveform predicted by numerical relativity. There is no need for you to confuse the two.

AS: For example formula of free fall: F= mg is proved by the experiments.

It is, but we also know it is wrong. Any theory is only trusted within the range over which it has been tested and applies equally to the GW detected by LIGO. The actual detector output waveform matches the predicted value to an error less than the measured noise.

The fact that there is an output proves they exist and so far they waveform also confirms the GR prediction. We can hope that as the noise is further reduced and more event are recorded, we will find some deviation from GR that will point is the right direction for a more comprehensive theory.

AS: 3. Change of beams length was not measured directly be rulers.

A ruler is any instrument that measures distance and the SI unit for distance is the metre. I suggest you look up that definition, you will discover that using an interferometer is a direct measurement of the change of length.

If the speed of light in the volume containing instrument changed, it would affect both arms of the instrument and produce no output. Because gravitational waves are transverse and quadrupole, they lengthen one arm while shortening the other (then vice versa in the next half cycle) and it is that varying difference in lengths that creates the optical output, that is what the instrument measured.

[BHS = "black holes"]

I think guys that the first thing you should agree is what "black hole" means to each of you. Is it a mass contained within its Schwarzschild radius (or the Kerr equivalent) or is it just a compact mass that has exceeded the Tolman-Oppenheimer-Volkoff limit (or whatever is the upper limit for degeneracy pressure)?

I get the impression that the phrase means different things to different people (not just you two).

I agree with Arno, a GW will affect both arms of LIGO identically, I have explained my reasoning in the link below. 

http://groundpotential.org/forum/viewtopic.php?f=14&t=35#p113

AG: Dear George, I am not your guy. Please note.

I'm not sure what you mean Arno, it's just a generic term as far as I know, no offence was intended. Substitute "gentlemen" if you want it to be a bit more formal.

Steven, yes, your alternative would have the same problem.

Arno, my explanation is not a knee jerk reaction to LIGO, it's a theory I have been working on for 20 years, and it was always obvious to me that the  LIGO design could not work. I even made a $1 bet with a guy and lost. I paid up, but I still don't think LIGO can see gravity waves.

The reason is pretty obvious to me, a gravity wave is a disturbance in ground potential, it can't change the rest mass of a proton, therefore it can't move matter, it affects the observer only as it passes through, but this effect is isotropic. 

Arno, I couldn't agree more, it's a crazy situation where politicians who don't understand the science are ultimately approving the science, and once the gravy train starts moving it's hard to stop. It was totally predictable that LIGO would announce a gravity wave after receiving the increased funding. I can't think of too many cases where ground breaking science has been done by big projects like LIGO and the LHC, oh we may as well throw in ITER.

@ Valentin: You make a good point, the big bang theory has huge momentum and it will take a definitive experiment to knock it off course. Ground Potential will be taken seriously when we start seeing that electron is gaining mass with time. I estimate that GP is falling by 0.5 millivolts per year, so with current technology we should know this in 10-20 years for sure. 

Science is converted to a self-fulfilling prophecy rather than an eye to what really exists out there: LIGO report on 'gravitational waves detection'

That is the main issue for the moment!

https://www.linkedin.com/pulse/science-converted-self-fulfilling-prophecy-rather-eye-christopoulos?trk=prof-post

Data A detailed critical review of reported event GW150914 that L...

AS: I would like clear one thing here: WHAT HAS MEASURED LIGO?

I answered that back on page one, I'll repeat it here.

AS: As far I understood LIGO has measured variation of laser light velocity passing the beams.

If the passing wave changed the speed of light in the volume containing instrument changed, it would affect both arms of the instrument and produce no output. We have to be careful to consider proper versus coordinate effects but that's semantics.

AS: 1. that GW has shorten and prolonge the beams lenghts.

That is correct as I said before. Because gravitational waves are transverse and quadrupole, they lengthen one arm while shortening the other (then vice versa in the next half cycle) and it is that varying difference in lengths that creates the optical output, that is what the instrument measured.

AS: This is PURE NONSENSE from the point of fundamental methodology of physics

The methodology of physics is first to produce a mathematical theory (Einstein did that in 1915) and second to use it make predictions (the LIGO groups have been doing that using numerical relativity code for some years, the results were and continue to be published) and third to make measurements which can be compared with the predictions (which they did last September and possibly on several occasions since).

If the observations conflict with the predictions, the theory as it stands is not right and we get information that allows us to start working on an improved version. If they do match (as is the case here), the theory survives.

The same methodology also applies to all alternative theories, they too can be compared to the detector output if they predict wave detections that differ from GR.

@ George: I there an assumption in this statement?

Quote George "Because gravitational waves are transverse and quadrupole, they lengthen one arm while shortening the other (then vice versa in the next half cycle) and it is that varying difference in lengths that creates the optical output, that is what the instrument measured."

Gravitational waves may well be transverse and quadrupole, but by which mechanism  are they supposed to move matter? 

Spooky action at a distance?

Steven, perhaps my reply could have been clearer, I meant that they were quadrupole transverse in GR hence their detection is understandable. Other theories may predict a different format and different interaction with the instrument, but it would be for the proponents of those theories to calculate and test their predicted output.

They move matter in the same way that gravity moves anything else.

@George: only matter moves matter, I have never heard of space moving matter, have you?

George wrote: "Because gravitational waves are transverse"

Valentin wrote: Excuse me for being direct: transverse to what?

Transverse to their direction of propagation.

In other words, if we pick axes so that the waves are moving in the x direction lengths will be increased in the y direction while being shortened in the z direction. That is unlike sound waves which are longitudinal, the molecules are moved in the same direction as the propagation of the wave, but similar to EM where the electric and magnetic field vectors are perpendicular to the direction of propagation. The attached link shows the effect of a wave that is coming out of the screen towards you.

Of course their orientation relative to the LIGO detector arms is random and there will be a 'blind' region where the signals in each arm cancel. However, that's a narrow ring round the sky and since the two sites have different alignment, at least one will see any large enough signal so the system is sensitive to signals coming from almost anywhere on the sky.

Valentin wrote: Physics should be first about observing and then about describing, and later about predicting.

Scientists disagree, it's too tempting to 'tune' the calculations if you already know the answer so the highest confidence goes to equations that predict the result before it is known. For example, Newton's Law and GR were both used to predict the bending of starlight before Eddington's expedition in 1919. The Newtonian formula predicted half of that predicted by GR and the observation gave a result that matched GR. Deriving the calculation after the event is called "postdiction".

https://en.wikipedia.org/wiki/Gravitational_wave#Effects_of_passing

Steven Sesselmann wrote: only matter moves matter, I have never heard of space moving matter, have you?

John Archibald Wheeler wrote: "Spacetime tells matter how to move; matter tells spacetime how to curve."

https://en.wikiquote.org/wiki/John_Archibald_Wheeler

@ George: John Wheelers 's quote is not right, nothing can't move something.

Our world is made from stuff we call something and stuff we call nothing, so unless you want to reintroduce the ether, let's agree that nothing is nothing.

Space-time is not a volume, it's a singularity, a single point on the time line where past meets future and where space is perpendicular, this point is called the observer.

There are as many of these points as there are observers, and each one is completely independent of the other. I can't see a gravity wave passing through you and you can't see a gravity wave passing through me, because we are independent observers. 

---

This whole LIGO thing reminds me about the story of the kings new clothes, where a cheeky tailor who was handsomely paid, spent weeks sewing clothes for the king, telling the king and everyone in the palace that his threads and his cloth was so fine that only the smartest people would be able to see and appreciate it. When the tailor finally told the king that his new suit was finished the king decided to parade his new suit down the main street of the town, people of the town lined the streets and  watched in awe as the king paraded naked down the street, but no one said anything, except one small child who cried out and asked, why is the king naked?

---

https://en.wikipedia.org/wiki/The_Emperor%27s_New_Clothes

I wrote: "if we pick axes so that the waves are moving in the x direction lengths will be increased in the y direction while being shortened in the z direction."

Valentin wrote: No, that's a dipole transverse wave.

EM radiation is dipole. Think of the electric field, it accelerates a charged particle in one direction and we can represent that by a vector (transverse because it is perpendicular to the propagation). Gravitational waves aren't like that, they affect both perpendicular directions hence quadrupole.

Valentin wrote: If they are transverse and quadrupole, as claimed by relativists, then there are compressions on both Y and Z.

Have a look at the diagrams in the attached link, the electric version has "+" in the top left and bottom right but "-" in the top right and bottom left. The magnetic version shows "N" top and bottom with "S" left and right. The gravitational version is the same, compression along one perpendicular axis at the same time as expansion along the other. The link I posted earlier (repeated below) shows animations of plus and cross polarisations.

Valentin wrote: Did you know that the effects of refraction upon a ray of light traversing the Sun's atmosphere are about 15 times greater than the guessed effect of gravitation? 15 times! That's a lot. Have you ever heard any relativist talk about that? No.

Yes, many times (though not recently) when crackpots suggest it without doing the calculation. I've also seen the calculation done (a good few years ago) and the correct answer is that the refraction is roughly a million times less than the gravitational effect (though the refractive value depends on frequency).

I also note that the Hipparcos Mission had to deal with that effect and verified it to better than 1% close to the Sun but also measured it at high angles, beyond 90 degrees to the Sun where the Solar atmosphere is negligible, and the gravitational formula is correct. I've never heard a crackpot come up with an explanation for that fact.

Of course we also have the GAIA mission in space at the moment which will be measuring star angles about an order of magnitude better than Hipparcos, first results are due this summer.

Valentin wrote: it's well known that Eddington committed fraud by throwing away the results which didn't match the "predictions" of his idol (Einstein).

See the paper below, Eddington's analysis was valid given the performance of the equipment of his time. It's academic anyway, modern measurements completely confirm the gravitational value.

https://en.wikipedia.org/wiki/Quadrupole#Electric_quadrupole

https://en.wikipedia.org/wiki/Gravitational_wave#Effects_of_passing

http://arxiv.org/abs/0709.0685

Valentin wrote: Please don't start with the "ad hominem" attacks already.

Nothing personal, I was talking about conversations on Usenet in the 1990's.

Valentin wrote: And you didn't notice that the compression on one axis (Y) becomes expansion, and the expansion on the other axis (Z) becomes compression?

Of course, that's what makes it a wave, not a static displacement.

Valentin wrote: So that's why I said both arms of the interferometer suffer compression (and expansion) if the direction of propagation (X) of the wave is perpendicular to their plane Y-Z.

Correct, but they are 180 degrees out of phase, when one is compressed, the other is expanded and vice versa, and that reverses several hundred times a second in the case of GW150914.

Valentin wrote: And in that case the result should be null ...

Why do you think that? The output from the interferometer in your axes for example might be Ly-Lz so when Y is stretched you get a positive output but when it is shortened and Z is stretched you get the negative portion of the cycle. If Y and Z both stretched simultaneously, you would be right but that's not the format the detector was built to see.

If you rotate the M & M setup but keep the lengths the same, there would be no change. If you keep the orientation fixed but alter the arm lengths, then there will be a fringe shift. That is what LIGO is looking for. Shifts due to rotation (i.e. the Sagnac Effect) would be just noise. In the animation, think of one arm horizontal while the other is vertical and they meet at the centre. The reason why there will be an output should then be obvious.

Valentin wrote: In the M-M interferometer case, the said null result happened because, as FitzGerald and Lorentz hypothesized, the length of only one of the arms suffered a contraction. That contraction cancelled the shift of the fringe pattern which shift was supposed to happen due to the relative motion between Earth and aether (which would imply different times of propagation of light on each arm respectively).

Be careful, what you say is correct but "length contraction" is an effect that describes the difference between a separation measured in one frame and the same separation measured in another. In the MMX, it was the lab frame versus the aether frame. Here we need only consider one frame, that of the detector.

Valentin wrote: So I think the analogy between M-M and LIGO is correct.

Having thought about it a bit more, I agree in part. It is valid for the instrument but what is being measured is different. M&M were trying to find an anisotropy in the speed of light based on the prevailing assumption of Galilean relativity. As we now know, that assumption was incorrect and the speed light of light is isotropic in an inertial frame in special relativity hence they could not get an output. In the horizontal plane, SR was adequate to describe spacetime for their experiment (obviously there would be gravitational effect if it were performed in a vertical plane). For LIGO, the GW create transient tidal effects so an SR approximation is not valid.

The usual descriptions you see everywhere describe the output in terms of motion of the mirrors but you could equivalently think of the mirrors as static and the metric being stretched or compressed (I picture rubber rulers behind unmoving mirrors). Looking at it that way, if the speed measured against the rubber ruler stays at 'c', then the time for the light to travel the length of an arm will vary but again the key point is that the change is not isotropic. If the direction of propagation is the X direction, then the apparent speed in say Y would be increased while in the Z direction it was decreased (and as always vice versa on the next half-cycle).

Whichever way you choose to think of it, the important part is that GW have the opposite effect in the two directions perpendicular to the propagation and that is what is measurable.

Valentin wrote: (Note: I just meant a rotation of 90o for M-M, so I don't know where you got the idea of a Sagnac effect, as the Sagnac interferometer has a different construction compared to LIGO or M-M).

It was in response to this previous comment:

Valentin wrote: And I dare to say the interference pattern doesn't change even during the rotation at 2

Although the construction is different, if the light paths enclose a finite area there may be an output.  However, the LIGO setup isn't rotating so that's an academic question.

AS: First there is no SPACETIME in the universe there are SPACE and TIME.

It's some time ago but we discussed the Twins Paradox and I thought you agreed that "time is what a clock reads".

AS: Second SPACE is not curved, space is flat.

The large scale average is flat as far as we can measure (uncertainty about 0.4%) but over smaller scales it is curved producing effects we call "gravity" locally, and for example gravitational lensing over cosmological scales.

http://sci.esa.int/planck/51606-gravitational-lensing-of-the-cosmic-microwave-background/

Sorry Arno, but back in the real world, the LIGO detector did produce an output and it does match the signature of GW from the merger of two compact objects, so unless it turns out to have been an accidental artificial injection, you have been proved wrong. Burying your head in the sand won't change that.

I don't want to get into discussing the MMX per se either but it's important to be aware of why M&M got a null result but LIGO doesn't.

Valentin wrote: So, the stretching of the arms in LIGO happens gradually, as you see in that animation.

Well a couple of hundred times a second is quite fast for the orbit of a binary star system! The animations slow it down so you can see it.

Valentin wrote: And so I thought that transition, from the maximum compression on Y to the maximum compression on Z, would *correspond* to the 90o rotation of the M-M interferometer.

In the lab frame of the MMX, there is no variation of length though, that's the point I was making. What is called "length contraction" is a difference in measurements between two frames that are in relative motion but doesn't apply when considering the object's rest frame. In the MMX there was no variation of either arm length in their lab frame while in LIGO the lengths vary between stretched and compressed in a few milliseconds in the rest frame of the detector.

Valentin wrote: I'm still not convinced.

I'm cautious too but the possibilities for error are limited.

Valentin wrote: I don't know how they could have calibrated the interferometer in such a way that it guarantees that it suffers the GW effect starting from an "unstretched/uncompressed" position of the arms.

The rest condition doesn't matter too much, they are looking only for the rapid variations. The bandwidth doesn't go below about 10 Hz, the rest position would be like a small DC bias on an audio signal.

Valentin wrote: There is also inertia involved, ..

That's an interesting question but not a source of error, how could "inertia" create an AC swept-frequency signal?

Valentin wrote: there is also a possible different velocity of light involved,..

That's just an alternative interpretation of the effect of the wave but again would still imply the same wave existed.

Valentin wrote: and also a time delay of whatever processes involved (some might want to call it "time dilation").

Again we are working in the rest frame of the detector so time dilation does not apply.

Valentin wrote: Too many factors, ..

None relevant from what you have listed.

Valentin wrote: too much noise around,

Certainly that has always been the problem but the new design has reduced it significantly and in this case the signal was much larger than the noise.

Valentin wrote: too little probability of the occurrence.

The calculated predictions for this performance level are a few to hundreds per year so the 4 or 5 seen in 4 months is pretty much what was expected.

Valentin wrote: If you add the lack of the confirmation of the cosmic event in the EM spectrum,

For two black holes, none is expected. In fact the possible FERMI event would be hard to explain if it is associated with the GW.

Valentin wrote: and even other theories which argue that gravitational waves are not possible

Well those theories are simply falsified by the detection. That's why the crackpots will be desperate to find excuses for pretending it didn't happen ;-)

Valentin wrote: then you would understand the skepticism of many of those who hear about the experiment and who think about it.

Oh I do understand. You appear to be genuinely curious and are raising good questions, most others have their own pet theories and many of those are simply blown out of the water by that fact that GW do exist.

Any viable competing theory should not be threatened by this, they should have been checked against the Hulse and Taylor observations years ago. Bear in mind that the inspiral phase, which is the majority of the observed signal, follows the same equation as already verified by H&T.

I wrote: "In the lab frame of the MMX, there is no variation of length though, that's the point I was making. What is called "length contraction" is a difference in measurements between two frames that are in relative motion but doesn't apply when considering the object's rest frame."

Valentin wrote: That is what those who believe in Special Relativity claim. I personally believe in a different kind of theory, more akin to the Lorentz Ether Theory. So there you go, we have a religious conflict of opinions.

Not really, LET and SR are identical (if you include all the phenomena in LET) so it's only a matter of philosophical interpretation, both give the Lorentz Transforms for transferring measurements between frames, but as I said, we only need to consider the detector frame so both are moot.

Of course both are relevant only where gravity is negligible and since we are talking about gravitational waves, neither is very useful. The real question for you would be what equations you are going to use to model gravity. Then you need to see if they support a wave solution and what energy they will carry away from a binary system. If you get the same answer to those questions as given by GR, you'll get get the same signal prediction too and your alternative survives.

I wrote "The bandwidth doesn't go below about 10 Hz, the rest position would be like a small DC bias on an audio signal."

Valentin wrote: But what can be more anthropocentric in there than an audio signal?? So, what a coincidence!

Not really, the lower end is limited by seismic noise. The best sources for testing would be known binary star systems such as HM Cancri but that has an orbital period of 321 seconds, four orders of magnitude below the detectable range, and it is the fastest found so far.

Valentin wrote: So I guess if a theory out there would predict gravitational waves (GW) happening at frequencies in the MHz range, it would be ruled out by the current dogma of Physics.

Nope, there was a proposal recently for an experiment to search that range [see the attached link], and of course eLISA will be looking at much lower frequencies. In fact there was a summary of this given in the LIGO press conference, perhaps you should watch it.

Valentin wrote: After all, why would something be allowed to be happening in the Universe, if we are not yet prepared to detect it? So now, in the upside-down Physics of 2016, we first need to predict something which we are sure we can detect, and then we detect it and automatically prove some theory. That's exactly the opposite of how Physics developed between Galileo and Maxwell, but who cares?

Only your upside-down reasoning. We know for a fact that there are low-frequency binary sources out there but seismic noise prevents us building detectors in that range. To see them, we need a space-based mission.

Valentin wrote: The question is more: how could inertia *prevent* any signal, given the definition of inertia as the resistance of the matter to any change of its state of motion.

That's where the concepts of GR depart significantly from Newton's "absolute space and time". Of course in a sense we could say that it is the inertia of the two compact objects that kept them orbiting, and inertia also plays a role in allowing the LIGO mirrors to respond to the waves, but I don't understand how you think "inertia" could generate a false signal.

Valentin wrote: I've seen papers disagreeing with the existence of GW, which were written under the principles and the terms of General Relativity. So there you go, another religious conflict of opinions, this time inside of the same Church.

Well decades ago, it was a point of debate but the understanding of GR has progressed a long way since then and in particular over the last 15 years or so we have developed robust equations to the 3.5PN level. There are a few crackpots out there still trying to claim GR doesn't predict waves but they're wrong without any doubt even on a purely theoretical basis.

[edit: p.s. I've added a link to a paper on the high frequency wave detector]

http://arxiv.org/abs/1410.2334

Another p.s. related to your comment that we can only see the low audio band with LIGO, I just came across the linked article so you can see how wide the frequency range being considered can be. If only we had detectors over that range!

http://physics.aps.org/synopsis-for/10.1103/PhysRevX.6.011035

http://arxiv.org/abs/1511.05994

Valentin, I agree entirely that SR and LET are pretty well diametrically opposed in terms of concept but the basic maths ends up being identical, and since that is what gives us predictions from the theories, no experiment could separate them. Check the history, if there had been an experimental way of distinguishing SR from LET, someone would have tried to do it or at least published a paper saying how it could be done.

Valentin: you are starting to miss more and more the points of my counter arguments

I thought I had responded sufficiently but we can go over them again.

Valentin: such as the one about transitions between compressions

I agreed that your comparison with the MMX as an instrument is valid but pointed out that there is no rest-frame variation due to inertial motion given Lorentzian relativity (either SR or LET) while the tidal effects of gravitational waves do create relative changes in the LIGO rest frame. Basically, the signal being sought is quite different and the detector design is valid for that type of signal. Your objection is not valid.

Valentin: the one about the dampening effect of inertia

Inertia is a more complex topic as I said but naively you can look at it as inertia tries to maintain the location in the metric and that is what causes the mirrors to be moved as the wave passes, without inertia they wouldn't be affected.

Valentin: and the one about the fact that a theory should be developed *after* a phenomenon is observed, not before.

That's just plain wrong. First, Einstein developed GR based on known phenomena which he had already modelled using SR and the known effects of gravity, specifically Newton's Law which had been derived from the motion of the planets plus some new insights, notably the Equivalence Principle so GR was developed after the phenomenon known as gravity had been observed. Second and perhaps more important is that in the scientific community, a new is only generally accepted if it is better at predicting known effects (e.g. the precession of Mercury and gravitational bending for GR) but the most convincing proof is if it can predict phenomena before they are seen.

In fact that's the basis of the current debate raging around various forms of string theory. So far, they cannot make any predictions that differ from known science and until they do, hence can be tested, many in the rest of the community are treating them as "unscientific". Just being able to exactly replicate GR for example is considered necessary but insufficient.

Valentin: Also, a proposal for a detector of high-frequency GW is not the same as having an already constructed massive detector for the audio range

As I already explained, LIGO's low end range is limited by seismic noise and they've done all they could to combat that. Getting to lower frequencies requires a space mission and that is progressing albeit more slowly as the US pulled all the funds. I agree it's sad but that's a political problem, not scientific.

Valentin: not to mention that it's not clear what theories the proposed detector will prove.

When Galileo invented the optical astronomical telescope, he wasn't trying to prove any theories. LIGO and the other instruments are being built so that we can look at the universe in a new way. Any new theories will be built from what we see through them, and that's going to take a few years to build up a body of observations.

Valentin: illusory detection

The fact remains that a signal was detected whatever you might prefer. It seems to me that there are three possibilities, first it might be an accidental synthetic injection. I'm sure they will have done a lot of checking to eliminate that (as you point out, they don't want the embarrassment of the "BICEP2" story) but it remains a vague possibility. Alternatively it might be some natural phenomenon other than GW that merely created a similar signal. Nothing you've said has given any possible mechanism for that but it is by far the most likely if it wasn't GW. The third of course is that the observatory is working and we are starting to see what was always expected, and without some credible alternative explanation, that's the logical conclusion.

When Galileo invented the optical astronomical telescope, he pointed it at the moon and saw mountains on it, he didn't assume it was a perfect sphere as the religious view held and that the Moon's imperfections must be flaws in his lenses.

AS: NATURE has published article where is shown that GW research is dead.

That's hearsay Amrit, provide a link to the article.

Arno wrote: Dear George, you miss the point.  We are discussing this: It appears to me very unscientific to employ a hypothetical incredibly violent event in/of the universe involving a gigantic assumed collision of two alleged giant black holes the existence or content of which is, to say the least, among scientists, controversially discussed,

No Arno, we are discussing Amrit's points in this thread, not yours. Check the top of your screen.

Amrit said: 1. LIGO did not observe directly the interference pattern which is computer simulation.

That is simply not true, I assume Amrit misread the description of the waveforms. The detector output has been made available as well as separate predictions from numerical calculations.

Amrit said: 2. This simulation is based on the proposition that one beam is getting longer and other is getting shorter because GW is entering the interferometer. 

That statement is correct and much of the discussion, especially with Valentin, has been about that aspect.

I wrote: "Check the history, if there had been an experimental way of distinguishing SR from LET, someone would have tried to do it"

Valentin: There are already plenty of papers published about that distinction.

No experiments though, it can't be done because you can't distinguish an equation from itself.

Valentin: The fact that SRT has the same results as LET means one of them is wrong ..

No, it means either they are both right or both wrong. If Lorentz Invariance passes a test, then both theories survive, if the test fails, both are falsified. Gravitational effects aren't predicted by either for example.

Valentin: But look again in your replies. Do you see the word "transition" anywhere addressed by you? I didn't see it. So you missed again my point. Never mind.

Last try. Going back to page 5, you said: "So, the stretching of the arms in LIGO happens gradually, as you see in that animation. And so I thought that transition, from the maximum compression on Y to the maximum compression on Z, would *correspond* to the 90o rotation of the M-M interferometer."

That appears to be the only sense in which you used the word. When the MMX is rotated, the SR interpretation is that there is no change of length and the speed of light is isotropic hence no fringe change. The LET interpretation says that the arms change length but the speed of light is anisotropic, the speed being lower in the direction of length contraction, thence the two effects cancel on each arm explaining the null result.

In LIGO, the arms aren't rotated. The distance between the test masses increases in one direction but decreases in the other while the speed of light remains isotropic. One light beam is delayed while the other is advanced (it doesn't have so far to travel) hence the fringes move.

The instrument is similar but gravitational distortions being measured are quite different.

GD: "inertia tries to maintain the location in the metric and that is what causes the mirrors to be moved as the wave passes"

Valentin: How can inertia try to keep the location in the metric, while the location and the metric is supposed to be modified by the gravitational wave itself?? It doesn't make any sense to me.

OK, I'll answer this but its an area I'm still learning so my explanation may not be as clear as I might hope, it's just my best effort. The idea of "inertia" goes back to Newton's first law, a body moves at constant velocity in a straight line unless acted on by a force, and "inertia" is the constant of proportionality relating the rate of deviation from the constant velocity/straight line motion to the applied force. In GR, the straight line is replaced by a geodesic which is curved by gravitational effects. It is the transient curvature of the geodesics that is being measured. The natural path of the test masses with no forces acting on them becomes a sine wave of varying frequency and amplitude and inertia is what stops the masses deviating from the geodesics.

Valentin: You don't need to remind anyone the history of GR, as my point here was not a direct criticism of General Relativity. ... My point was that the phenomenon of gravitational waves was not put in evidence before.

It seems I do need to remind you, Einstein showed that the equations required the existence of gravitational waves a century ago.

Valentin: So you are wrong in equating a theory of gravitation (any theory!) with a presumed phenomenon of gravitational waves.

No, the GR equation require them. In fact that's why it is a test of GR, if theye din't exist, the equations would only be approximate, Like Newton's Law before them.

Valentin: There is no logical reason for any theory of gravitation to "predict" gravitational waves, ..

The maths requires that solution, they are not optional.

GD: "When Galileo invented the optical astronomical telescope, he wasn't trying to prove any theories." "When Galileo invented the optical astronomical telescope, he pointed it at the moon and saw mountains on it, he didn't assume it was a perfect sphere as the religious view held and that the Moon's imperfections must be flaws in his lenses."

Valentin: So? Your example is beside any point of the discussion.

It was a response to your comment in the discussion: "not to mention that it's not clear what theories the proposed detector will prove."

Valentin: Are you claiming that LIGO was built without the purpose of trying to prove any theory? Anyone can also build an experimental device which might or might not yield any result, as Galileo did. However, no private person, not even Galileo, could ask $620 million for a lottery device.

Think about that a bit more. I could say "they have detected one gravitational wave so that proves the prediction and now they can dismantle it, it has served its purpose". Get real. Nobody would spend that amount of money for a one-off. The reason it was built was to be an observatory that should run for decades and give us a great deal of information that couldn't be obtained any other way. It wasn't a "lottery" either, not since the work of Hulse and Taylor. It's interesting to wonder if LIGO would have been funded without the H&T evidence but once it was shown that their system was losing energy at the rate predicted by GR, that energy had to go somewhere and should therefore be detectable.

Valentin wrote: I don't have the money to do such experiment on my own. But I'll do it one day,

Before you do, calculate what values you would get (a) if LET is correct and (b) if SR is correct. I'll give you a hint, if you do the calculations correctly, the two predictions will be identical. If you find different answers, either there's an error in your maths or more likely you missed one of the LET phenomena.

If you're trying to use the "one-way" speed, usually it is the relativity of simultaneity that people miss but obviously I don't know what you are doing so these are just cautionary notes, intended to be helpful.

As for your 'conspiracy theory', you should note that one way of gaining credit in the scientific community is to show that previous results were wrong, hence misleading. If Virgo or Kagra doesn't give similar results (allowing for differences in sensitivity), then they will publish and show the US were being "over-optimistic". The US know that.

Valentin : SRT claims that there should be zero aberration of light in any inertial frame

That is not true. For example if the motion is perpendicular to the line of sight (theta=90 degrees) you have:

Galilean relativity predicts tan(theta - phi) = -v/c (but that model fails the MMX anyway)

SR and LET both predict sin(theta - phi) = -v/c

See the links for details.

https://en.wikipedia.org/wiki/Aberration_of_light#Classical_explanation

https://en.wikipedia.org/wiki/Aberration_of_light#Relativistic_explanation

"The motion of what??"

The motion of the Earth relative to the star (or vice versa). That motion is what creates aberration so if v=0, all three theories predict no aberration at all and the whole thing would be pointless.

However, a test would require watching the aberration over a year and measuring the variation due to the change of apparent location due to the component of the Earth's orbital motion at 30km/s around the Sun. Everything else is constant (the motions of the star and Solar System around the galaxy) so subsumed into the apparent average location.

In practice, even the difference between arcsin and arctan at that small value of v/c is not measurable.

No, the fault is mine, when you talked of aberration, I automatically thought of Bradley's measurements of "stellar aberration" which were relevant to some early aether theories. The term aberration means a displacement caused by motion of the observer relative to the source so there is none in the experiment you describe.

Valentin: Lasers will be calibrated to go along the arms from the common point of the arms towards measurement targets placed at their respective ends, and then measured after those arms' various rotations.

The output of the laser will always be perpendicular to the output mirror in the lab frame or in the aether rest frame. If you think of the motion of the laser through an aether, the light path has to be slightly angled so that it hits the mirror on each subsequent reflection if the laser is moving hence it will still hit the target. The geometry will cancel out any possible detection.

Give it a bit more thought before putting any money into it ;-)

Valentin wrote: there won't be any reflections involved

Perhaps you haven't looked up how a laser works, that's what I was talking about.

Valentin wrote: The effect was observed by NASA in their Lunar Laser Ranging experiments

The Moon is moving relative to an inertial frame centred on the Earth.

I was talking about the reflections between the end mirrors inside the laser.

Valentin: So it is the target at the end of each of the arms of the device I want to build.

I though you said the lasers would be used after the "various rotations" hence the targets would be still at that time:

Valentin: Lasers will be calibrated to go along the arms from the common point of the arms towards measurement targets placed at their respective ends, and then measured after those arms' various rotations.

Valentin: After the arm is rotated, the laser beam will miss the chosen point, thus hitting the target at a nearby point

Nope. At about 1:40, you show that in the video. Try thinking about how you would draw the simulation but also showing the internals of the laser with the light bouncing between the mirrors a couple of times before escaping. The path is such that the light will hit exactly the same point on the target.

Valentin: George, light does NOT follow the arm with the rotation of the arm.

I didn't say it did. In any inertial frame, the light will travel in a straight line in the direction it was launched.

Valentin: And please stop mentioning mirrors. There are NO mirrors involved.

Of course there are, you said you were using a laser. In any laser the light is reflected from the ends of a cavity to allow the "amplification" which is the "A" in the name. From the link you provided:

"As in other lasers, the gain region is surrounded with an optical cavity to form a laser. In the simplest form of laser diode, an optical waveguide is made on that crystal's surface, such that the light is confined to a relatively narrow line. The two ends of the crystal are cleaved to form perfectly smooth, parallel edges, forming a Fabry-Pérot resonator. Photons emitted into a mode of the waveguide will travel along the waveguide and be reflected several times from each end face before they exit. As a light wave passes through the cavity, it is amplified by stimulated emission, but light is also lost due to absorption and by incomplete reflection from the end facets. Finally, if there is more amplification than loss, the diode begins to 'lase'."

The "incomplete reflection" is what allows some of the light to leave the device, and if that is too high a fraction, you just have an ordinary LED, not a laser. If say 1% escapes, then on average the light is being reflected ~100 times.

The orientation of the reflective surfaces or "mirrors" is what determines the direction of the light at emission and the path thereafter doesn't curve.

My apologies to Amrit, the conversation has drifted from the original question.

Valentin, I think there is a risk that we are talking past each other a bit. Can you just clarify, are you talking about a deflection from the target that occurs while the apparatus is being rotated or are you only making measurements before and after the rotation but not during it?

Valentin: Such claim is false, because light is not part of any inertial frame

A "frame" is a mathematical coordinate system. I can define any system I like and the light can be given coordinates at different times in that system. The location light can of course be defined in any inertial frame.

Valentin: light does not follow the frame of the source

I never said it did, I said it travels in a straight line in an inertial frame. If the source is rotating, a co-rotating frame is not inertial. If you are only making measurements before and after, that doesn't apply though.

Valentin: You simply can't comprehend that the laser and the arm are at rest with each other, so when the arm rotates 90o then the laser will rotate as well by the same angle, including its internal waveguide. So the direction of emission of the light will be rotated 90o just fine.

If the arms rotate 90o and so does the beam, the light will still hit the same point on the target, that was exactly the point I was making. That is valid if you don't measure during the rotation.

Valentin: In conclusion, light is *forced* to be emitted in a new direction, but once it was emitted it cannot be forced to *follow* that direction as seen in the source's frame at the emission moment.

That's true so the light will follow a straight path as I said which means it will hit the target unless the arms are rotating while the light travels.

Valentin, some of your comments seem to imply measurement during the rotation but others exclude that so I'm unclear what you intend.

Valentin wrote: The measurements are done only before and respectively after the rotation not during rotation. The measurement before is just for the calibration.

Excellent, thanks for clearing that up.

Valentin wrote: The measurement before is just for the calibration.

Fine, so once that is done, the reflective surfaces in the laser are exactly perpendicular to the line between the laser and the target. That will remain true once the apparatus has been turned.

Valentin wrote: light does not follow any straight path given by an inertial frame... The motion of the wavefront is given by the vectorial c - v

Exactly, and in this case both c and v are constant vectors so their sum is also constant hence the path must be a straight line.

Now consider how the light is reflecting within the laser. As the apparatus moves through the aether, the light path looks like the attached image (borrowed from something on light clocks). The portion of the light that escapes one mirror continues the same straight line path it had between the last reflections. That angles it sideways (in this view) so it hits the centre of the target.

https://upload.wikimedia.org/wikipedia/commons/thumb/3/32/Light-clock.svg/539px-Light-clock.svg.png

Valentin, there is usually no waveguide in a laser, just two mirrors. Sometimes a waveguide can be implemented but that is just to eliminate all but one mode which improves the spectral purity, but the direction is still set by the mirrors.

Valentin: First that image of the light clocks is wrong. Second, it refers to a totally different situation, so I don't know why you are constructing a straw-man attack here.

It isn't a strawman, I was careful to point out that I got it from an unrelated site just to save time drawing the sketch. The point is that a laser is a source of light trapped between two mirrors and that sketch shows what happens even though it was drawn for a different purpose. The distance between the mirrors is irrelevant as you correctly point out but the directions are valid and after the light passes through the end mirror, its path is just a straight extension of that inside.

Valentin: The vector c2 after rotation is perpendicular on vector c1 which was used at calibration. So there are two very distinct resultants: c1-v and c2-v. 

You misunderstood. What you say is correct but the point is that c1-v is constant so the direction is a straight line and c2-v is constant so that is also a straight line. Of course the two are nearly perpendicular but each is straight.

Valentin: With repeated measurements in different directions and calculations that will eventually give the value of v

No, it will give you a null result, there will be precisely no displacement of the beams on the target.

Valentin: of course in the absolute space the resultants are straight,

Excellent, that is what I was saying all along. They will also be straight in any other inertial frame, just in a different direction relative to the frame, but that's an aside.

Valentin: That is because v remains *constant* and keeps its orientation in absolute space, while c1 rotates 90o and becomes c2.

I know, that's why I said "nearly". Now the point is that the slightly reduced angle is what causes the beam to hit the target since it is also moving at v.

Valentin: No that's not an "aside ...

It is, I was only talking about other frames to wrap up the earlier discussion, e.g. as seen by someone walking past the equipment.

Valentin: Look again at the simulation video. It's plain and clear what's happening.

I agree, it's a nicely drawn and explanatory simulation, but the paths it shows are wrong. Think in the aether frame if that's easier for you. The mirrors and target are all moving with velocity v. The light moves with the vector sum of c+v as you said. That means that the v components cancel out and there  is no nett displacement relative to the original point on the target where the light hit during calibration.

Note also, that is true whether you apply Galilean or Lorentzian.

Your equations you posted previously were right, you just need to calculate through to finding the amount of displacement. Do it fully and you'll get zero for the answer.

Fair enough Valentine, I'll give it one more try then I'm done, I'm only trying to save you some wasted effort.

I've drawn a diagram showing one arm of the apparatus you propose in the two configurations. To make it easier to see, I've assumed you just happen to be in a lab moving through the aether at speed v in a direction exactly aligned with the arm when you calibrate. That is shown at the bottom. The two mirrors in the laser are marked "M" while the target is "T".

Above that, I've shown what happens when you rotate the apparatus by 90o. I've shown the setup in four locations with the light bouncing off the mirrors and the beam emerging from the top mirror towards the target. It should be obvious why the beam will hit the same point on the target. If I animated it, the light would always progress from the mirrors to the target along a line joining them.

To make it easier to draw, I've neglected the motion of the mirrors and target in the calibration orientation, it would only change the length of the red line.

Valentin: You simply don't understand how a wave guide works

I'm a senior principal engineer in a communications company and currently validating a new radio transceiver design. I do know how wavesguides work, but they are irrelevant, there is no waveguide involved.

However, you don't know how lasers work. A laser uses two mirrors to recirculate the majority of the beam, without that you don't get enough gain to start lasing action.

Valentin: and you are representing the situation incorrectly as it would be the M-M experiment.

I'm representing how a laser is constructed with two mirrors, one partial, for the light source. The target is assumed not to reflect the light.

Valentin: So it was incorrect from you to assume the ray would go through the mirror and then move towards the target.

That's how lasers work. You talked of using a laser as the source, perhaps that was a slip and you had something else in mind but you've had enough opportunities to tell me I had misunderstood if that were the case.

What you've shown in the first of your images is a good illustration of what "multi-mode" behaviour in a laser would look like if you mirrored the ends of the fibre. It is possible to use a waveguide to prevent multiple modes and single mode fibre is used to prevent dispersion caused by the different speeds of different frequencies.

Valentin: Try to draw the separate directions of the motion of target and respectively the wavefront so they meet in the same point

I'm not going to spend any more time on this but you could download my image and add them if you like. To work out the wavefronts within the laser, the beam must hit the same point on the back mirror each time. The wavefronts are then perpendicular to the beam direction within the laser and those in the external beam must be parallel to those inside which means the beam direction is simply a straight line extending the beam inside. That means the beam hits the target at the same point in each orientation.

https://sustainablenano.files.wordpress.com/2013/02/laser2.png

http://www.prosoundweb.com/images/uploads/FiberOpticsGraphic1.jpg

"A waveguide is needed to have the beam emitted in a certain direction."

Valentin, go and read up on lasers or just look at the images I posted before, you are talking nonsense.

"Once the wavefront is emitted out of the active medium, further there are lenses, and or other waveguides, involved to clearly direct that beam and not to have the beam emitted in a random direction."

You can manipulate the light after it leaves the laser with any devices you like but as a source itself, there are no lenses or waveguides required to construct a laser. I have a He-Ne tube sitting on a shelf at home and I can assure you it contains just a hollow plasma chamber and three mirrors (triangular configuration for a ring gyro). There are no lenses and no waveguide. Have you ever handled a raw laser tube?

Valentin: There are many types of lasers which use solid active media or point-like media.

Sure, you can use many different materials to produce the raw light but the thing they have in common is a cavity with reflection at the ends to get sufficient gain. Otherwise there is no laser action, you just get a non-coherent glow. Coherence requires that new photons are emitted in phase with the existing ones so there must be a population inside the cavity. It is the mirrors that define the direction of the beam within the laser, nothing else.

Valentin: So you're imagining your own barriers, not mine.

There's no "barrier" to doing what you propose, a laser diode will work just fine, but no matter what source you use, the geometry means there will be no beam deviation after the rotation, it will still hit the target at the same point where it did after calibration.

Valentin, the argument is shown in the geometry I drew for you, that is as much part of physics as any other method of explaining it. The light emitted from the laser must always be normal to the mirrors and your calibration ensures that normal hits a specific point on the target. Rotating the setup doesn't change what you established so won't alter the impact point.

In Galilean aether theory, the mean speed would be affected (which is what the MMX looked for) but even there you wouldn't get a deflection. To hit a different place on the target while still being launched normal to the laser mirrors would mean the path had to curve, and (I think) we agree the path will always be a straight line.

I'm talking simply about how a laser operates. All you have is an otherwise isotropic light source between two mirrors. Those mirrors are the only part of the device that can determine the emitted direction of the beam. Simulated emission means new photons are transmitted in the same direction as those already in the device to give a coherent source but that process doesn't determine the direction, the mirrors do. Once you grasp that, you can figure out the rest for yourself.

Good luck with that.