Quote:
Originally Posted by DavidNg
What is the "speed" of gravity? I dare ask, ie how long would it take for the earth to spin-off from the moment of sudden disappearance of sun's gravitation force.
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This is a problem which puzzled scientists until Einstein came along.
If gravity travels at a finite speed, the Earth would advance a certain distance in its orbit before gravity would influence it.
Somehow gravity had the ability of acting on this advanced position before the Earth reached it.
A simple solution would be to claim that gravity travels at at infinite speed.
In General Relativity gravity has a rather different meaning.
The Earth is travelling along a path in curved space time. Gravity is "felt" as a reaction force much like the sideways centrifugal force acting on you as your car is driven around a bend.
Since gravity is a reaction force, the speed of gravity is no longer a relevant issue.
Gravitational waves on the other travel at the speed of light.
If the Sun disappeared, gravitational waves (if they exist) would blast Earth out of its orbit in around 8 minutes.
Regards
Steven