- Does a photon in a box undergo cosmological red shift over time?
When a photon travels from a distant galaxy to us it undergoes an increase in wavelength due to the expansion of the universe during the time of flight. On the other hand, physical objects such as atoms and galaxies do not undergo a similar expansion because they are bound together by elctromagnetic and other forces. My question is this: suppose you put one or more photons into a box which has 100% perfectly reflecting walls. Will the photon(s) in the box experience a cosmological red shift over time or not? If so - why? and if not -why not?