# Gravity is faster than light?

Take two objects like the Earth and the sun. Before light can reach the Earth from the sun the distance between them would need to be defined. Gravity is what defines this distance, right? So gravity would have to get here first before the light did. The only way this happens is that the speed of light is shifted less than what it is to the stationary Earth observer. However light is actually faster than this speed once Earth starts moving. If gravity was not faster than light how could it escape from a black hole?

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gravity is/curves space-time. Whatever gravitational effect it propagates at c - at least we think so. Light moves "on" space-time. It does not need to be space-time "emitted" together with the light, it is space-time as it is at the time light passes that particular point.

Light and gravity does not move with a purpose they move according to the local space-time and, for the earth-sun system, eventually reaches us ... or doesn't as it might turn out (could pass by, right!?)

Nereid
Staff Emeritus
Gold Member
What sort of experiment could you suggest that would test, in principle, the difference between c and 'the speed of gravity'?

The whole point of general relativity was when Einstein found out that Special Relativity meant that gravity would be limited to the speed of light. This is when Einstein realized that Newton's Universal Theory of Gravitation. The main point is finally we had an idea of what gravity was... it being warps in space time. To see how this idea developed you might want to check out this article I wrote. I would like to type a more detailed response but i got to get some sleep. I have ACT's tomorrow

Nereid
Staff Emeritus
Gold Member
GR is a really cool theory, and has been tested (in some domains) quite well.

However, one 'prediction' - that the 'speed of gravity' is c - could perhaps be tested more directly* or more stingently; how?

*it's already been 'tested' indirectly; IIRC the 'relativity' corrections to celestial mechanics (for example) would be out of kilter with what we actually observe if the speed of gravity were not c.

(BTW, in the article, I think Tom means 'eluded', not 'illumed' )

well thanks for reading it lol I will go fix that now :/