aramis720

Strange, I've addressed in detail in this thread (last week) why the argument that apparatus and light are affected differently doesn't add up. So now I'm seeking clarity on why the mirrors are thought to move. And I've suggested the 2D thought experiment with lines on a balloon as a way to start with the basics. Can you answer my question about that? Do you agree that any expansion or contraction of the balloon will not be detectable using the lines themselves or any coordinate system based on the lines? And if so why wouldn't this apply equally to the 3D version? I'm not asking you to repeat prior points or give me equations. I'm asking you to think about it from a basic logical perspective.

We've been focusing on the Faraoni 2007 explanation here in the last week and his argument is that the mirror positions do in fact as a result of the GWs, but that light wavelength is not affected by the GWs. I've been trying to get to the bottom of the notion that the mirrors move by using a 2D metaphor as a simplification of the 3D/4D reality: two perpendicular lines drawn on the surface of a balloon, with coordinates drawn on the lines. I'd appreciate any further thoughts anyone has on this. Do you agree that the coordinates on the perpendicular lines drawn on the balloon's surface can't be used to detect any expansion or contraction of the balloon itself b/c they change in exactly the same ways as the balloon? If so, why would it be different when we go to the 3D/4D actual interferometer? I've argued that it wouldn't b/c the meter stick (the interferometer arms and their effect on the light fringe phase) itself is changing to exactly the same degree that space and spacetime are being distorted. It doesn't matter in what way we distort the balloon in the 2D metaphor, or the underlying space or spacetime in the 3D/4D reality, if we are in fact using a "meter stick" (the interferometer in these examples) that is itself situated in the dimensional reality that is changing. To measure such changes we need an additional degree of freedom, a higher dimension. So in the 2D example we need a third dimension to be able to measure the change, as we can achieve in our own 3D reality by actually performing the balloon experiment with perpendicular lines drawn on it. And to measure the 3D/4D changes created by grav. waves in our actual reality we'll need a higher dimensional vantage point that alas is not available to us as mere 3D/4D dwellers.

Thanks for the dialogue Mordred. I'd hoped we could at least work through this 2D metaphor but no problem if you're not game. Think it through some more and you may see my broader point about the comparable 3D interferometer difficulties. We've been focusing on the Faraoni 2007 explanation here in the last week and his argument is that the mirror positions do in fact move from the GWs, but that light wavelength is not affected. I've been trying to get to the bottom of the notion that the mirrors move by using a 2D metaphor as a simplification of the 3D/4D reality. Since Mordred has decided not to continue with the dialogue I'd appreciate any further thoughts you have. Do you agree that the coordinates on the perpendicular lines drawn on the balloon's surface can't be used to detect any expansion or contraction of the balloon itself b/c they change exactly the same amount as the balloon?

I didn't say anything about not using coordinates. You misunderstood me. Again: do you agree that any coordinates on the perpendicular lines in the 2D metaphor can't be used to detect any expansion or contraction of the balloon because they will expand and contract exactly the same amount as the balloon itself?

So do you agree with my point about the 2D metaphor?

That's not my point. Again, staying with the 2D metaphor: if you expand or contract the balloon do you agree that there is no way to measure this expansion or contraction using just the perpendicular lines? Please don't move ahead of this point. I'm trying to establish where we agree and then explore where we start to disagree.

By definition the coordinates on the perpendicular lines won't change in a detectable manner no matter how much the balloon is distorted. Do you agree? They will simply expand or contract in a manner that is entirely undetectable based on the perpendicular lines themselves.

So how would you know that one axis contracted and the other expanded in my 2D visual metaphor, by using the perpendicular lines only?

Wait, you're refusing to address my simple visual metaphor? Why would you not address this question after our long discussion?

You didn't address my metaphor still. I can't force you But I think it might be helpful. Do you agree that in my metaphor there is no detectable expansion using the perpendicular lines?

That's not my metaphor that I was asking about. Again: envision two perpendicular lines on the surface of a balloon (a 2D version of an interferometer). Now expand the balloon. Will the length of either line change in any detectable way using the lines themselves? Of course they won't b/c they're expanding in exactly the same way as the balloon. Now expand the metaphor to three dimensions.

With respect to the lines drawn on the balloon of course the distances change exactly the same way. You can't use the lines themselves on the balloon to measure these changes. Does that make sense?

And how does the quadrupole wave relate to my metaphor of lines drawn on a balloon?

Again: you haven't addressed my basic logical objection and I hope you will. I'm addressing the fundamentals here. The basic logic. That hasn't been addressed and until we can get past that step the foundation is not firm. I'm not asking about the mathematics -- I'm asking about the basic logic. Everyone is being confused by the higher order concepts and mathematics and skipping over the basic logic of how the apparatus is supposed to work. "Look, here are the equations that show it works, but let's ignore the basic logic of the situation."

I know you have repeated your assertions and I mine but you haven't yet addressed the basic logical objection. Here's a visual metaphor: think of a balloon with two perpendicular lines drawn on it. If the balloon expands the two lines will expand in exactly the same way as the balloon so there will be no way to detect the expansion by using the lines only. You have to take a higher level viewpoint outside of the balloon to know that it has expanded. Does that make sense?

I said it doesn't matter what direction the waves are coming from -- it could be any or all directions and 1 or a hundred different waves. Based on simple logic, if the apparatus that occupies space is stretched to exactly the same degree as the space it occupies it cannot detect the waves. Think it through. It will sink in eventually.

That doesn't matter. Obviously if the apparatus is being stretched in exactly the same manner as space is being stretched it doesn't matter what direction the wave comes from.

Ok, so in plain language, at the level of concepts, how would the physical apparatus change in any measurable way when of course that apparatus is being waved in exactly the same way as the space it occupies (in every direction)?

Yes, a wave of water travels through water but also through space more fundamentally (space is, after all, the container of all things). Any measurement device to measure the water wave is in the water but more fundamentally is in space, and it will not be distorted itself by the passage of the water wave (in terms of its fundamental dimensions). To the contrary, and my point this whole time, is that any device in space that is designed to measure waves OF space will be distorted in exactly the same way as the space it occupies, making detection in principle impossible. Is that clear? In terms of the recent critiques of the GW data, see my article for the rebuttals and responses, etc., with the initial group critiquing the work standing by their critiques.

I'll respond further to the recent points made, but this just in casting serious doubt on the recent findings re gravitational waves: https://www.quantamagazine.org/strange-noise-in-gravitational-wave-data-sparks-debate-20170630/?utm_source=Quanta+Magazine&utm_campaign=fa74101318-EMAIL_CAMPAIGN_2017_07_07&utm_medium=email&utm_term=0_f0cb61321c-fa74101318-389689705

beecee, I've mentioned a couple of times already in this thread that the chance of my being correct is very minimal. I'm not even a physicist, but I am trained as a scientist and critical thinker and have written some in the philosophy of physics. That said, I still haven't seen my concerns addressed well in this forum or elsewhere. You suggest, as have many others in this thread, that there is in fact a differential effect from GWs on the physical arms of the interferometer, based on the different directions of the arms. But this is manifestly incorrect when we recognize that GWs are defined as waves of spacetime itself. So, as I've stated numerous times since my OP, this definition of GWs seems to render any detection of such waves by a physical apparatus in principle impossible simply because any distortion of spacetime itself will distort the physical apparatus occupying that slice of spacetime by exactly the same amount as the wave itself, in every direction. So the direction of the wave doesn't matter. I'm not sure why this point isn't sinking in, but as I just mentioned to Mordred it seems that a lot of people continue to envision GWs as traveling through space rather than being waves of space itself. Thanks for the post on GR but I'm not here challenging GR itself. I'm just asking about the LIGO experiment and GWs.

Mordred, your discussion reveals that you are thinking of the GW traveling through space (and I think this is the general conception among physicists), but as I've pointed out many times now GWs are defined as waves of space, not waves traveling through space, as described on p. 679 of the Faraoni paper. So, no, the arm lengths will not be affected differently in any detectable way because the space they occupy is being distorted in exactly the same way as the apparatus that occupies that space, regardless of the direction of the waves and the vectors at issue. Again, the key point: GWs are defined as waves of space itself. The only reason, it seems, that Faraoni and Thorne conclude that the mirrors move is because of the simplifying but opposite assumptions I discussed previously with respect to the mirrors and the wavelength of the light.

Mordred wrote: The key point is you have a difference of two seperate field interactions. Treat the arms as a matter field with its own coupling constants. Then treat the photon or electromagnetic field with its own coupling constants. The differences (differentials between these field intaractions can be measurable). Then add on top of the above differences in polarity via the quadrupole nature of spin 2. The differences between x and y arms. Mathematically speaking, which at this level heuristic explanations do not work well is quite detectable. One of the calibration tests of lead weights previously mentioned, demonstrates the degree of variations. That is the trick different fields exhibit different medium like reactions to types of fields. It is the differences we look for. (more often than not under symmetry relations described as anistropies) anistropy being in essence a non uniform relation. It is challenging to recognize these differences without the mathematical background but it is the differences in information exchange between each type of field both within each field and how each field interacts with other fields that is detectable. Reread the articles you mentioned and look for the differences of information/interaction exchange vs matter and radiation type fields. All interactions generate interferance. The nature of different interferences between different field compositions is important. Seek the differences at every geometric event ( coordinate) at a moment in time not every location responds identically The paper you mentioned describes two key dynamics. Differences in how two medium like fields interact. But also polarity differences of the two arms via spin 2 vs frequency of wave relations. Key note those variations has a term under physics ... the quantity of Strain. not easily described for GW waves...at least not heuristically under math easily.(granted knowing how the math applies being essential). Particularly with different fields/mediums.( yes there is a distiction) aramis720 responds: Ok, indulge me here please. Here are the key passages from Faraoni 2007. He discusses three recent explanations for why LIGO could in theory detect GWs, including Saulson 1997, a presentation by Kip Thorne, and Garfinkle 2005. He ends up concluding that Thorne's version is accurate and he provides what he considers to be a solid mathematical foundation for it. Here's his comment about Thorne: "'…the influence [of the GWs] on the light is negligible and it is only the mirrors that get moved back and forth and the light’s wavelength does not get changed at all …'. However, substantiating Thorne’s answer with a clear mathematical argument is not entirely trivial, as is shown in Sect. 3." He then attempts to demonstrate that indeed it is the mirrors that move and the light's wavelength doesn't change under the influence of GWs. In section 3, he states, with respect to the motion of the mirrors (p. 682): "Under the assumption λgw >> L the spatial dependence of hαβ can be neglected and ... Therefore, in the approximation used, the laser photons do not suffer spatial deflections to first order." He adds at p. 683: "In the approximation λgw >> L the temporal variation of h11 (t) during the short time ≈ 2L it takes for the light to travel to the mirror and back is negligible and δλ [is approx. equal to] 0 in this approximation." And with respect to the mirror positions and arm lengths, Faraoni states the effect is "different from zero" (p. 683): "In the approximation λgw >> L the time dependence disappears and del x/L = h+(t = 0)/2, Eq. (4.2), which is different from zero..." But one could just as well argue that this "different from zero" result should also be considered negligible in the approximation lambda >> L. No numbers are offered in this paper with respect to the negligibility decisions. More importantly, we are back to my OP question: WHY would the GW have any effect on the arm length and the mirror positions when the GW is distorting spacetime to exactly the same degree that would make it in principle undetectable? I also note that the explanations offered in this forum have changed remarkably as the discussion has progressed, beign initially focused on the notion that it is in fact the change in phase that is detectable. If we're focusing now on the Thorne/Faraoni explanation, a quite different explanation than the earlier explanations, we seem to have a major problem in explaining at the level of basic physics and logic why there would be a differential effect on the mirrors and the light. You mention differential field effects, but what is the basic rationale that undergirds the different mathematical treatment here? WHY would these fields be affected fundamentally differently? Why are the coupling constants different? In terms of fields and distortions of spacetime a good metaphor is the sagging or bulging sheet (which is spacetime). If the GW is defined as a distortion of the sheet, the fields that occupy spacetime are influenced the same way by such distortions, as a matter of principle. Suggesting that it is the TT gauge approach that is the source of the difference just substitutes a different set of assumptions without explaining the basic physical differences (it seems to me). Again, light and the physical arms are occupying exactly the same physical space that is being distorted by the GWs. The mathematical explanations offered by Faraoni don't really attempt to address why the different simplifying assumptions are warranted in each case and he doesn't recognize in the paper that the different assumptions lead to opposite effects and it is ONLY these different simplifying assumptions that lead to the differential effects. He states at the end of the paper (p. 684): "Physically, the interferometer works by measuring the differential stretching of the x and y arms while the high frequency light wave essentially experiences no inhomogeneities in the 'medium' in which it propagates—the gravitational wave—because the wavelength λgw of the gravitational wave is so much larger than the wavelength of light. This conclusion agrees with Thorne’s qualitative answer to the objection." As we know from the alleged detection events, the physical effect being measured is very small indeed -- that's why it's taken so long to get a clear signal (albeit a false positive, it seems to me). So with a very small signal attempting to be detected, it seems a bit strange to argue for negligibility ("essentially experiences no inhomogeneities") of physical effects resulting from the GWs with respect to wavelength, but for non-negligible effects with respect to distortion of the mirror positions and the arm lengths. Particularly when the physical rationale for why the mirror positions would be affected has simply not been offered anywhere.

Yes I read the paper through and attached my highlighted version. My point was that the mathematical treatment of the physical effects in one case (the arms) interprets the GW effect as "negligible" while the effect on the light beam is considered significant, but both outcomes are a result of simplifying BUT OPPOSITE assumptions. And as I've stated too many times already this makes no sense bc the light waves and the arms occupy the same space. There is no principle offered for why the effect should be different on the two different physical phenomena. Rather, it seems to be a rather veiled attempt at incorrect mathematical sleight of hand to create an effect that logically can't exist. Do you see my point? Or am I misreading the paper?

Diving back into this topic after I've had a chance to review in detail various papers that address the question (how can LIGO detect gravitational waves when any distortion of the interferometer arms would seem to be in principle undetectable b/c the detecting device is distorted by exactly the same amount as the waves sought to be detected) and I find the answers unconvincing. The easiest to follow and the latest paper that I've found so far is Faraoni 2007: https://link.springer.com/article/10.1007%2Fs10714-007-0415-5?LI=true After reviewing Faraoni 2007 and these other papers (including Melissinos 2003 and Garfinkle 2005) it seems that this alleged detection of GWs by LIGO is incorrect. Check out the Faraoni paper and let me know what you think. Basically it presents a number of mathematical steps for calculating the changes in the interferometer arm lengths and light waves, from GWs, that rely on a number of assumptions that shift the calculations one way or the other and then the paper pronounces "Presto! We've shown that we can in fact detect GWs because there's a different effect on light than on the arms from the GWs," but the allegedly differential effect found seems to me to be entirely a consequence of the simplifying assumptions, which in one case are thought to be negligible and in the other significant. The basic problem remains: how could GWs be detectable, in principle, by a device that occupies a slice of spacetime that is being waved to exactly the same degree by the GWs sought to be detected? I've attached Faraoni 2007 with my highlights.