Here's the explanation about how we know gravity waves travel at light
speed. First some background. About 1.3 billion years ago, two massive black
holes spiraled into each other and collapsed into a single black hole.
Initially the two black holes circled each other slowly, picking up speed
for a billion years or so as they became closer, and in the instant before
they merged, they were moving at about half the speed of light. Their
collision released a vast amount of energy in the form of a gravitational
wave, with a peak power output equal to roughly fifty times the power of the
entire visible universe. The frequency of the wave was equal to the period
of the two black holes as they circled each other, and in the instant before
they merged into one, the frequency of their rotation was in the audio
frequency range. The wave was actually a chirp, because the frequency
increased rapidly as the black holes spiraled ever more rapidly into each
The gravitational chirp traveled at the speed of light until it reached us
1.3 billion years later. We know how fast it was moving because there were
two synchronized detectors, one in Louisiana and the other in Washington
state. The chirp arrived at the Washington detector first, and then about 7
mS later, it arrived at the Louisiana detector, which was the transit time
for light. That is in accord with Einstein's theory. The recordings of the
chirp waveform are also in complete agreement with general relativity
predictions about black holes. By the way, these detectors are huge objects
several Km across and cost more than a billion dollars.
> ------------ ORIGINAL MESSAGE ------------(may be snipped)
> On Mon, 21 Nov 2016 13:22:01 +0000 (UTC), you wrote:
> >The speed of light.
> Being a rather skeptical bunch here, we need a bit more convincing.
> How do you know?
> 73, Bill W6WRT
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