If you could build a box with a reflective inside that no light could escape. If somehow you put a laser in the box and fired the beam and then shut off the laser what would happen? Would the beam continued to bounce off of the insides of the box or would the beam dissipate somehow? If it does dissipate, where does the light go without an escape point? I personally think that it would dissipate, I don't however have a clue where the energy goes. It becomes a different form of energy obviously, but what... got me.