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In replying to a recent question I stated:

Gravitational waves have not been yet experimentally observed so as to have their velocity measured.

Which after the fact prompted me to try and verify it. I found a "speed of gravity" claimed measurement, which has been in a controversial discussion. In the last paragraph of this wiki article I found:

In September 2002, Sergei Kopeikin and Edward Fomalont announced that they had made an indirect measurement of the speed of gravity, using their data from VLBI measurement of the retarded position of Jupiter on its orbit during Jupiter's transit across the line-of-sight of the bright radio source quasar QSO J0842+1835. Kopeikin and Fomalont concluded that the speed of gravity is between 0.8 and 1.2 times the speed of light, which would be fully consistent with the theoretical prediction of general relativity that the speed of gravity is exactly the same as the speed of light.[18]

There has been criticism, described in the paragraph.

Has this matter been resolved ? is the measurement valid?

The speed of gravity has also been calculated from observations of the orbital decay rate of binary pulsars and found to be consistent to the speed of light within 1% ( same link).

This is the speed that gravitational fields transfer information, and though the number itself depends on the theoretical framework solving for the system parameters it is true that just the existence of gravitational damping in the binary system would imply that the speed cannot be infinite.

Along these lines I was wondering whether studying the second star in a binary system where the first has gone nova would not give a cleaner and model independent measurement of the speed of transfer of information gravitationally. In this day and age where everything is digital one should be able to have data on this from now on.

LIGO has officially (Feb 11,2016) announced the observation of gravitational waves , at the same time consistent with the speed of light being c, and thus measuring it. See the webcast for a summary.

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anna v
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  • This and this related Phys.SE question also ask for experimental evidence. – Qmechanic Oct 07 '12 at 09:21
  • I can tell you that binary pulsars give good data on this because they are easily observed and have nice regular orbital characteristics (I would think star-NS systems would get messy from the gas exchange and accretion), can be resolved into two objects, thanks to being pulsars, and they radiate comparatively significant amounts of power in gravitational radiation. – Zo the Relativist Oct 09 '12 at 00:28
  • But I'm no observational astronomer, either. – Zo the Relativist Oct 09 '12 at 00:31
  • @Qmechanic I find that Carl Brannen 's answer in http://physics.stackexchange.com/questions/5456/the-speed-of-gravity , the second link in your comment, answers my question best. I had not seen it. – anna v Oct 09 '12 at 03:56
  • @CarlBrannen maybe you could copy your answer from http://physics.stackexchange.com/questions/5456/the-speed-of-gravity here, then I could choose it. – anna v Oct 09 '12 at 03:57
  • related: http://physics.stackexchange.com/q/68070/4552 –  Jun 14 '13 at 22:24
  • Of course, one can not only focus on finite-speed effects at the source, but also on finite-speed effects here at the receiving end, much as Ole Rømer did with light. See today's arxiv post, for instance: http://arxiv.org/abs/1304.0369 –  Jun 20 '13 at 07:19
  • @annav: Hi! Updated your question about the recent detection. –  Feb 14 '16 at 03:08
  • @user36790 thanks for digging it out :). – anna v Feb 14 '16 at 06:16
  • Anna, did the recently announced detection of gravitational waves at LIGO really confirm that the wavespeed for gravitation is the same as for EM? or was that only assumed when they did the beam-forming calculations to indicate the general direction of the source of the wave? won't they need at least one more LIGO facility (like in Italy) to experimentally confirm wavespeed? – robert bristow-johnson Feb 20 '16 at 05:30
  • @robertbristow-johnson The signal is consistent with the velocity being c . Do not forget there are two detectors and the time delay is consistent with the geometry and a c velocity. Of course the more detectors and the more distant the better. IMO consistency is also a measurement. – anna v Feb 20 '16 at 05:47
  • no, a different wavespeed can be used that would result in the source coming from a different angle. that 7 ms delay is consistent with a variety of different wavespeeds along with their corresponding angles of incidence. i think they need at least one more detector to verify wavespeed. perhaps not if you can see the phenomenon along with measuring the gravity wave. – robert bristow-johnson Feb 20 '16 at 05:50
  • @robertbristow-johnson but is there a gravitational theory that would explain it with a velocity different than c? We are not talking of seismic waves here , we are talking of space distortions. – anna v Feb 20 '16 at 06:31
  • that's sorta changing the subject @annav. what i am referring to is direct experimental evidence of the wavespeed of gravitational waves. certainly the LIGO results are consistent with GR and GR says that the wavespeed is $c$. but that is not yet the direct experimental evidence. but, i think, the next time something like this is detected, if there are 3 or more detectors and the event is detected in all 3 and their clocks are working and synced, then i think you will have that direct evidence. – robert bristow-johnson Feb 20 '16 at 19:53
  • the LIGO results did put a top limit on the wavespeed. i don't think the wavespeed can be much more than 140% $\times c$ with a 7 ms time difference between the detectors spaced apart by 3000 km. i dunno what the chord-length is between the two detectors. but even if the wave front came along perpendicular to the line connecting the two detectors, it can't be faster than about 140% $c$. – robert bristow-johnson Feb 20 '16 at 20:01
  • @robertbristow-johnson What about the numerical simulations at the source? I suspect, they would give a significantly different result even for a little bit different $c_G$. – peterh Jun 06 '17 at 17:31
  • Speed of Gravity: https://arxiv.org/pdf/1909.00881.pdf – Attila Janos Kovacs Feb 13 '24 at 02:15

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It is difficult to design empirical tests that specifically check propagation at c, independently of the other features of general relativity. The trouble is that although there are other theories of gravity (e.g., Brans-Dicke gravity) that are consistent with all the currently available experimental data, none of them predict that gravitational disturbances propagate at any other speed than c. Without a test theory that predicts a different speed, it becomes essentially impossible to interpret observations so as to extract the speed.

Has this matter been resolved ? is the measurement valid?

Kopeikin was wrong. See:

The speed of gravity has also been calculated from observations of the orbital decay rate of binary pulsars and found to be consistent to the speed of light within 1% ( same link).

This is not really correct. GR predicts that low-amplitude gravitational waves propagate at c. The binary pulsar observations are in excellent agreement with GR's predictions of energy loss to gravitational waves. That makes it unlikely that GR's description of gravitational waves is wrong. However, it's not a direct measurement of the speed of gravitational waves. There is no way to get such a measurement without a viable theory that predicts some other speed.

Along these lines I was wondering whether studying the second star in a binary system where the first has gone nova would not give a cleaner and model independent measurement of the speed of transfer of information gravitationally.

The fact that a star goes nova doesn't produce any abrupt change in its gravitational field. If mass is expelled, there will be a gradual change.

  • thanks for the links. Maybe I should have said supernova, instead of nova, to get a lot of the mass ejected. I do not understand the requirement of a necessary other theory.Suppose one star becomes supernova over a few days, the change in the orbit of the companion would depend on the gravitational speed . Of course a theory is necessary to get numbers out. – anna v May 04 '13 at 19:34
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    @annav Unfortunately, that is very hard. Supernovae outshine normal stars by roughly the same ratio as the Sun outshines the Earth, so seeing the companion is very hard, even if it were in our galaxy. And almost every SNe seen in modern times is millions of light years away, so any companion is too dim to see anyway. Moreover, it's not clear what change you expect to see. The orbit won't change until ejecta mass/energy has moved beyond the companion's radius, no matter how fast or slow gravity information moves. –  Jun 20 '13 at 07:08