The speed of light in a medium is often lower than in the vacuum but does the same apply for gravitational waves. Is the speed of gravity in all media the same as light in that medium?
This question Do gravitational waves slow down as they pass through matter? has already a answer but it is not clear what the cause is that GW are not slowing down. Compared with EM-waves, which are in contrary slowed down, the reason for that wasn't dipole density but 'Its just the electrons not moving "instantly" with the changing electric field.' But is it sure that there isn't any particle of a medium in case of GW which also doesn't move instantly with the change of GW?
