Proving gravity waves

[danshawen]

Translation: BNS orbital decay data can and has been numerically equated to standard linearized GR quadrupole GW emission formula, but there is to date no direct evidence via LIGO etc. We all know that. The extent to which such interferometry-based setups can be considered 'local' was discussed in those earlier threads. There have to actually be GW's there for the differential techniques to reveal any such - as discussed in those threads. Point is though your comments above are skew of the main misinfo appearing in #16 ('local' restriction), #17 (equating a hoped-for GW wavelength with some small multiple of the relevant planetary orbital size). Wrong, and wrong - as discussed in those earlier threads.

Many I think actually read them, but agreed the understanding bit is often lacking. There are various possible reasons for the latter.

Fine, and good luck with that. No wonder guys like Schmelzer think they can just toss out relativity's assumptions and somehow bring back the aether while keeping GR's results.

You all seem to think, the problem with Michaelson Morely was that the interferometer JUST WASN'T SENSITIVE ENOUGH. No, that isn't even close to the right answer.

LIGO "wasn't sensitive enough" either. So, you don't think the 1/3 wavelength analysis is correct. Where is your calculation of a typical gravity wave's wavelength? What exactly would render such a wave immune to analysis that holds for every other kind of wave, both EM AND MECHANICAL, and on all scales?

 

[Q-reeus]

You all seem to think, the problem with Michaelson Morely was that the interferometer JUST WASN'T SENSITIVE ENOUGH. No, that isn't even close to the right answer.

Indeed, but methinks you are erecting a straw man. I'm not aware of anyone here at Sf with even a mediocre grasp of SR who thinks other than that MM null result was owing to fundamental physics. Consistent with both AE's 'no ether' SR, or the relativistically invariant ether of Lorentz - LET.

LIGO "wasn't sensitive enough" either. So, you don't think the 1/3 wavelength analysis is correct.

Off on another skew tangent again. The declared position of Advanced LIGO folks is general expectation of 'several-to-many' positive and confirmed detections per annum, beginning Sept 2015, with further relatively modest upgrades/tweaks over time. But check the past literature for pre-Advanced LIGO, and there was a definite 'quiet optimism' of positives back then that was quietly and progressively pared back as the silence became more and more deafening. We shall see if that changes from now on.

Where is your calculation of a typical gravity wave's wavelength?

Given the propagation speed is taken to be c just as for EM radiation, there is no mystery to λ = c/f, with f just twice the inverse of orbital period T. I'll leave it to you Dan to check what that comes out to for Sun-Jupiter system, and compare that to the light crossing time for such an orbit. Will give you a fair idea of the true λ involved.

What exactly would render such a wave immune to analysis that holds for every other kind of wave, both EM AND MECHANICAL, and on all scales?

GW detection a la Saulson analysis, is somewhat more subtle than for detection of EM or acoustic waves, given only effect of spatial metric gradients are in principle detectable. But basic theory seems viable IF such GW's exist. Repeating myself - but then again, we seem to be immersed in perpetual Groundhog Day!

 

[danshawen]

there is no mystery to λ = c/f, with f just twice the inverse of orbital period T.

Good answer. The wavelength of the gravity wave from the Sun-Jupiter system will be 12 light years. No distance that is closer than 4 light years distant will be able to detect or resolve any gravity waves from this system. Now I have more precisely defined what I mean by "local".

 

[Layman]

Gravitational waves were originally discovered by an attempt to describe a distant solar system. I don't really recall who or where. Then I have had my doubts about this original discovery, since telescopes have not been advanced enough to be able to detect planetary bodies. It would make me think that detecting gravitational waves in a similar method in our own solar system would be a great accomplishment, and it would rule out a lot of doubt about gravitational waves.

 

[PhysBang]

Gravitational waves are a consequence of General Relativity. The strongest evidence for their existence is the decay in the orbit of two pulsars orbiting each other. The orbit decays in exactly the amount predicted by the gravitational waves that should be emitted by the two stars.

http://www.astro.cardiff.ac.uk/research/gravity/tutorial/?page=3thehulsetaylor

 

[Q-reeus]

Good answer. The wavelength of the gravity wave from the Sun-Jupiter system will be 12 light years. No distance that is closer than 4 light years distant will be able to detect or resolve any gravity waves from this system. Now I have more precisely defined what I mean by "local".

Your figure of ~ λ/3 is evidently around the traditional optics diffraction limit for resolving adjacent objects - which has what to do with ALIGO/VIRGO/eLISA type interferometer setups? The theory of which recognizes a number of fundamental physics principles as setting ultimate GW detection limits, none of which correspond to your GW λ/3 figure. Do you intend on or have already contacted the theorists involved in those projects, and warned them of how far out, and indeed outright conceptually faulty, iyo their theoretical estimates are? Duty of care to do so I would have thought.

 

[danshawen]

Your figure of ~ λ/3 is evidently around the traditional optics diffraction limit for resolving adjacent objects - which has what to do with ALIGO/VIRGO/eLISA type interferometer setups? The theory of which recognizes a number of fundamental physics principles as setting ultimate GW detection limits, none of which correspond to your GW λ/3 figure. Do you intend on or have already contacted the theorists involved in those projects, and warned them of how far out, and indeed outright conceptually faulty, iyo their theoretical estimates are? Duty of care to do so I would have thought.

Better, I think, but not yet. I do have some considerable kinks to work out with the ideas which suggested this approach, and not all of those are original either.

Obviously, gravity waves associated with the orbit of the planet Mercury for instance would be much shorter than those produced by the Sun-Jupiter system, but the signal via GW production would also be far weaker.

But no matter how you make the GW, there is no avoiding the fact that an interferometer setup of whatever practical length you would care to make it is going to fall far short of the THRESHOLD OF DETECTION of 1/3 wavelength and that is my basic point. So by an independent means of calculation, I have basically rendered the same result suggested by special relativity. You can't possibly measure GWs locally.

 

[trevor borocz johnson]

http://www.sciencedaily.com/releases/2016/01/160108083918.htm
I suggested creating gravity waves from circulating mass on December 5th. Now this guy says he's got it.

 

[Q-reeus]

http://www.sciencedaily.com/releases/2016/01/160108083918.htm
I suggested creating gravity waves from circulating mass on December 5th. Now this guy says he's got it.

You really ought to try and keep up with what's already there: http://www.sciforums.com/threads/gravity-waves-detected-for-the-first-time-ever.154848/
[Wrong link. Right one: http://www.sciforums.com/threads/measuring-the-curvature-of-spacetime.154259/]
And no, the *proposal* not-actually-done is not about generating gravitational waves, just incredibly tiny static or quasi-static gravitational fields. Just what the point is with such an intrinsically heroic and expensive super sensitive interferometer based experiment escapes me. At best, it will simply confirm what nobody doubts - that an EM field generates a typically minuscule gravitational field just as demanded by the stress-energy tensor on RHS of EFE's. Yawn.

A far more interesting proposal to generate 'artificial' GW's in the lab was made and actually tested some years ago:
http://www.technologyreview.com/view/412674/if-superconducting-sheets-reflected-gravitational-waves/
http://arxiv.org/abs/quant-ph/0601193v7
(actually, iirc there were several proposed experiments by that researcher, but in either case, I do recall the one undertaken was, unsurprisingly to me, a failure.)