Another thought I had too was regarding "the speed of light" "slows down" through a medium. Like someone said here earlier, the speed of the photons do not slow down. The light traveling through glass for example is being constantly refracted until the light escapes the medium. From one refraction point to the next, the photon is still moving at c. But to it "seems" that the light traveled slower through the medium because it took longer to work its way through. If I have two roads that start at the same point, A, and end at the same point, B. One road is a straight shot from A to B and the other road is curvy. If I travel at 100mph on both roads I will get from point A to point B faster on the straight road than on the curvy road, but I was traveling 100mph the whole time.