This thread is for stupid questions. Or just mine. Whatever. Think ideal conditions vs. reality here: Suppose you had a large, IDEAL sphere composed of a material that was a perfect one way mirror with the mirror finish on the inside. The outside to inside direction would be perfectly transparent while inside to out would be perfectly opaque and reflective. Light could enter from the outside with no loss of energy, but it could never leave the sphere, bouncing around for eternity. 1. If you flashed a brief pulse of laser pen light into the sphere from the outside, what would someone see positioned at the center of the sphere (before possibly going blind from retinal damage)? 2. As photons can only enter and never leave the sphere, it seems that the sphere's material should get warmer. But in our case, with a perfectly reflective surface, would the photons be able to impart any of their energies to the sphere's material? I suppose in order to be a "perfect reflector", photons would have to be absorbed and then perfectly emitted with zero energy difference and no change to the kinetic energy of absorbing/emitting atoms of the mirror. Or not? 3. And finally, as more and more photons would enter the sphere and never leave, the total energy within the sphere should increase, limited only by what? The integrity of the sphere's structure? But if we began the experiment with a perfect vacuum - nothing at all inside the sphere - how would that continuous increase in energy manifest itself? As heat imparted to the sphere's structural material? Getting back #2, wouldn't our initial stipulation of perfect reflectivity prevent that possibility?