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I was reading a Wikipedia article on speed of gravity, https://en.wikipedia.org/wiki/Speed_of_gravity .

The following quote is taken from the mentioned article.

In the relativistic sense, the "speed of gravity" refers to the speed of a gravitational wave, which, as predicted by general relativity and confirmed by observation of the GW170817 neutron star merger, is the same speed[1] as the speed of light (c).

The speed of gravitational waves in the general theory of relativity is equal to the speed of light in a vacuum, c.[2] Within the theory of special relativity, the constant c is not only about light; instead it is the highest possible speed for any interaction in nature. Formally, c is a conversion factor for changing the unit of time to the unit of space.[3] This makes it the only speed which does not depend either on the motion of an observer or a source of light and / or gravity. Thus, the speed of "light" is also the speed of gravitational waves, and further the speed of any massless particle. Such particles include the gluon (carrier of the strong force), the photons that make up light (hence carrier of electromagnetic force), and the hypothetical gravitons (which are the presumptive field particles associated with gravity; however, an understanding of the graviton, if any exist, requires an as-yet unavailable theory of quantum gravity).

...

The detection of GW170817 in 2017, the finalé of a neutron star inspiral observed through both gravitational waves and gamma rays, currently provides by far the best limit on the difference between the speed of light and that of gravity. Photons were detected 1.7 seconds after peak gravitational wave emission; assuming a delay of zero to 10 seconds, the difference between the speeds of gravitational and electromagnetic waves, vGW − vEM, is constrained to between −3×10−15 and +7×10−16 times the speed of light.[29]

Is it correct to say that experimental verification that the gravity propagates at the speed of light came around 2017 once LIGO and VIRGO detectors observed the gravitational wave?

I assume that the curvature of space-time and gravitational wave are the same thing. I take space-time curvature as something static and gravitational wave as a dynamic and travelling curvature of space-time. Please correct me if I'm wrong.

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General relativity tells us that gravitational waves move at the speed of light, and there is lots of experimental evidence to support general relativity. So before 2017 there was already a lot of indirect evidence that gravitational waves travelled at the speed of light. So much so that no physicist I know thought otherwise.

But what changed with GW170817 was that we observed the same event both optically and with a gravitational wave detector. This was the first direct experimental evidence that gravitational waves move at the speed of light. Or at least approximately the speed of light since there was a delay before the optical detection.

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  • $\begingroup$ Thank you! Could you please confirm the following part? I assume that the curvature of space-time and gravitational wave are the same thing. I take space-time curvature as something static and gravitational wave as dynamic and travelling curvature of space-time. $\endgroup$
    – PG1995
    Dec 19 '20 at 11:28
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    $\begingroup$ @PG1995 yes the curvature of space-time and gravitational wave are the same thing. Compare this with an electric field: we can have a stationary electric field, as around a stationary charge, and we can have travelling electric fields i.e. EM waves. $\endgroup$ Dec 19 '20 at 11:32

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