Lets say, we got a cube, the inside walls are mirrors, and its a vaccum. If u light a spark or any light in there, and shut it off, will the photon keep going eternally reflecting inside the cube?

 

My take is:
If the coefficient of transmission and absorption are zero or in other words if coefficient of reflection is 1, I think then we will have eternal reflections of photon inside the cube.
Practically a small amount of radiation will always be lost but a large number of photons might still be trapped. The situation here is somewhat reminiscent of how an almost perfect black body can be made practically.

 

Since there is rarely perfection in nature, I suspect the photon will either find a hole to leak out of or a imperfection in the surface, and be absorbed, after so many bounces. Think of a pool table with the balls in continous motion, eventually the table will be empty.

 

okk..
ty guys, i just was curious about that