I'm not sure if this question is valid or not. I'm in Modern Physics now, and we just did relativity. I understand lorentz transformations, how maxwells equations can give the speed of light, and so on. What I think I'm asking is a philosophical question (maybe it can be phrased as something like "what is time without light?" - or "why does time dilation DEPEND on light".) I understand how/what happens, and the math (at least at the undergraduate level) behind it, but its still bugging me. Note: this question arose when we started thinking about time dilation.