It's said that nothing can travel faster than the speed of light, can someone explain exactly why this is thought? I know photons have no mass and in a vacuum obviously no resistance, but those aren't the only factors that apply to speed, are they? What about the "propulsion" of light? I also read something about that objects decrease in length...or something of the likes...and decreasing to 0 at c. This may be all wrong, but I can't find where I read that. (T'was on howstuffworks, but I can't find the piece) If that's true, I'd appreciate it if someone could explain that to me.