The speed of Gravity?

By Nils Rognerud, San Francisco, USA

According to Einstein’s Theory of Relativity, distortions in spacetime caused by mass – also known as gravity – will propagate out at the speed of light. In other words, the light from the Sun and the gravity of the Sun should disappear at exactly the same time from the Earth’s perspective.

I enjoyed reading this paper on the speed of gravity, by Prof. Tom Van Flandern. 

“Anyone with a computer and orbit computation or numerical integration software can verify the consequences of introducing a delay into gravitational interactions. The effect on computed orbits is usually disastrous because the conservation of angular momentum is destroyed.

Expressed less technically by Sir Arthur Eddington, this means:

If the Sun attracts Jupiter towards its present position S, and Jupiter attracts the Sun towards its present position J, the two forces are in the same line and balance. But if the Sun attracts Jupiter toward its previous position S’, and Jupiter attracts the Sun toward its previous position J’, when the force of attraction started out to cross the gulf, then the two forces give a couple.

This couple will tend to increase the angular momentum of the system, and, acting cumulatively, will soon cause an appreciable change of period, disagreeing with observations if the speed is at all comparable with that of light. See Figure 1.”

Prof. Tom Van Flandern also says:

“…gravity is once again taken to be a propagating force of nature in flat space-time with the propagation speed indicated by observational evidence and experiments: not less than 2 x 1010 c.”

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