on the speed of light: I believe that refraction refers to the bending rather than the slowing down of light - it simply takes longer as refraction (bending) causes the path to be longer and thus the apparent slowdown. Is the speed of light constant? Studying black holes some observers have indicated that the speed of light may be influenced by gravity. At the poles of black holes radio waves have been observed to escape along the polar axis at HALF the speed of light(much slower than normal but pretty good considering the circumstances). I believe that I heard that from Dr Kaku's radio program - it should be at mkaku.org, but you'll have to look around on that site for it. - TJ