Light in a sphere

If you put light inside a sphere, and the sphere was made out of reflective material - the light should bounce around it forever, right?

What would happen if you shinned a lazor in it? More and more light would get added,

Ok, I can abide this no longer.

Let us suppose that the mirrors are perfect reflectors
Let us suppose that there are no dead spaces between the mirrors (i.e. there are no edges that the light can strike that will cause it to stop reflecting so much)
Let us suppose that our huge spherical mirror also formed a perfect vacuum where there were no atoms or free particles in the space.
Let us suppose that this perfect sphere were able to defy any effects of quantum mechanics and it was able to keep all particles from ever entering within the space.


Now, with all of those assumptions, would the stream of photons continue forever?  No.  Why?  Because while photons are fairly stable, they still have a half-life.  There would come a moment in time when all of the photons will have simply broken down and the energy that the photons once were made of will be absorbed by the mirror itself.  The 2nd law of thermodynamics would take over within this closed system.

Would the light become more intense?  No.  Why?  Because that would violate the first law of thermodynamics.  Since light is made of photons, and since photons of specific frequencies have specific energies, then you cannot create more photons just by colliding the reflections.  It just doesn't work that way.  There would have to be an increase in energy in order to increase the intensity of the light.