PDA

View Full Version : Is gravity faster than light?



Doe, John
2008-Mar-13, 04:50 AM
I don't know much physics, but I seem to remember that Einstein's General Theory (or was it the Special Theory, see, I'm clueless) implied that whatever mechanism propagated gravitational effects was limited to light speed.

If this is correct then can doppler effects on gravitation also be observed?

This is just a random question that has been burning my brain for no apparent reason.

Tim Thompson
2008-Mar-13, 05:43 AM
So far as we know, gravity propagates at the speed of light. But whether or not gravitational waves are subject to cosmological redshift effects is something I do not know.

John Mendenhall
2008-Mar-13, 04:58 PM
I see no reason why they they shouldn't. All we have to do is detect them. But that's another story.

Yes, gravity propagates at the speed of light. As I recall, the orbital decay for neutron stars matches the predictions of GR, and that implies c as the propagation velocity.

Newtonian mechanics, which is a subset of SR, which is a subset of GR, assumes that the propagation velocity is infinite. Newton knew this was wrong, but didn't know why, but he knew it worked (in this special case, which he didn't know was a special case). See the Wiki article on the 'Speed of Gravity', it leads to a lot of other interesting subjects.