Hello all. My understanding of why light will "slow down" when going through a medium such as let's say a diamond is because it only appears to slow down. In reality the photons are absorbed by the electrons in the medium (let's say diamond) and then those electrons of the diamond re-emit new photons of light. So in reality the original beam of light is not slowed down but gradually absorbed and the new beam that comes out the other side of the diamond is comprised of new photons emitted from the electrons of the diamond particles. But the question is, if the photons that enter the diamond are absorbed and cause the diamond to give off new photons, does the diamond lose any sort of mass (as infinitesimal as I realize it would be). So is it conceivable that a light shone on a diamond for billions or trillions or quadrillions of years will eventually "erode" that diamond in the same way that water erodes rocks by causing the diamond to lose electrons a little at a time?