I've heard that gravitational waves travel at the speed of light, and have some parallels to electromagnetic waves.
EM waves slow down as they pass through matter (speed of light in glass is slower than in vacuum, for instance). Do gravitational waves also slow down as they pass through matter?
If so, are there any effects like Cherenkov radiation when matter passes through a medium at a speed greater than the velocity of gravity in that medium?
Do large masses like stars or Jupiter act as ball lenses for gravitational waves?
Best Answer
Unlike electrostatic charges, mass is always positive, so that there is no dipole density to deflect gravitational waves as they pass through a material. So the answer is no, not in an analogous way.
The main effect is the gross retardation of gravitational waves by matter the same way that they retard light, by focusing. This is just the bending of light/gravitational-waves associated with gravitational lensing.