Hello everyone, I'm new here: I just wanted to ask one question that was bothering me. You see, I've just started reading about modern physics; for example, quantum physics and general relativity - and their possible unification through superstring theory (yes, I'm reading "The Elegant Universe"!). Anyway, my question is this: First off, you need to be familiar with the theoretical "light clock", where a photon travels between two mirrors, and its used to keep time. The experiment showed special relativity, by demonstrating that if observed in movement, the proton will take longer to hit each mirror, and therefore time will move more slowly. So my question is simple and probably easily answerable: what would happen if the light clock was moving at light speed? Here is a picture of the "light clock" (it seems they have actually made one). http://www.physorg.com/newman/gfx/news/LightClock.gif Thanks for your time guys.