[Mentors' note - this post was forked off from this thread because it's an interesting question in its own right] I would also like clarification on this. if you throw a rubber ball at concrete, it will "bounce off". if you throw the rubber ball at mud, the mud will absorb it and it will stay there. however both the mud and the concrete have absorbed some of the rubber balls energy, just different amounts. is this the same with photons? could you reflect light indefinitely..