Lets say you had a box who's inside walls were perfectly reflective. In addition to this, because you are just so very awesome, you are somehow able to put a lamp inside that box that doesn't interfere with and of the light rays in the box except to produce more. Now since this is a silly and impossible set up, I'm going to ask some silly and ridiculous questions about it. 1) Would the box get more massive? 2) Would the box eventually have to "pop?" 3) If it was broken open, would there be a flash of light before it dissipated? I welcome answers, more questions related to this, and snide comments about how pointless it is to wonder about these things.