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This link and this one concern a recent measurement, by Chinese scientists, of the speed of gravity using Earth tides. They find it is consistent with a speed equal with the speed of light, with an error of about 5%.

Is it real? Was it done before another way, with better precision? Is it something particularly important for the validation of gravitation theories?

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related: – Ben Crowell Jun 14 '13 at 21:54
Minor comment to the post (v1): Please consider to mention explicitly author, title, etc. of link, so it is possible to reconstruct link in case of link rot. – Qmechanic Mar 20 '14 at 10:03
up vote 6 down vote accepted

K.Y. Tang is a geophysicist who is known for work on the Allais effect, which is pathological science dating back to the 1950's, when Allais claimed anomalous effects on a Foucault pendulum during an eclipse. A Google Scholar search shows no citations yet to Tang et al.'s February 2013 paper claiming to have measured the speed of gravity. As is often the case with pathological science, there seems to be a certain set of people who take the subject seriously and cite each other's papers, while people outside their circle can't be bothered to debunk them. This particular subgroup includes kooks like van Flandern, who has claimed, for example, that light propagates faster than $c$.

As discussed in the answers to this question, we have strong indirect confirmation from binary pulsars of GR's prediction that gravity propagates at $c$, whereas attempts at a direct measurement have been thwarted by the lack of any test theory that predicts any other speed for gravity. As with the previous bogus claim by Kopeikin, Tang et al. seem to have made no effort to seek the involvement of anyone competent in general relativity to help with analyzing and interpreting their data.

A Google Scholar search shows a couple of papers, Amador 2008 and Duif 2004, that reference Tang's previous work on the Allais effect.

Amador, "Review on possible Gravitational Anomalies," 2008,

Duif, "A review of conventional explanations of anomalous observations during solar eclipses," 2004,

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The result of a research team in China is faked and wrong

In Ref.[1], it is pointed out that Tang and coworkers’ result cannot be obtained from normal process and their result is faked.

In Ref.[2] it is concluded that their result seems to be drawn based on the misinterpreting of the known formula and the less careful data analysis.

Reference [1] Y. Zhu, Measurement of the speed of gravity, arXiv:1108.3761 [2] C. G. Huang, The observation of the Earth tide is irrelevant to the speed of gravity, Chin Sci Bull, 2013, 58: 3291–3294

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Dear zhuyin: For your information, Physics.SE has a policy that it is OK to cite oneself, but it should be stated clearly and explicitly in the answer itself, not in attached links. – Qmechanic May 26 '14 at 21:47

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