Why is glass "QM transparent"? Sorry if this is a basic question. Why is a wave state preserved through it's interaction with glass, mirrors, air, etc.? Why doesn't reflection (absorbtion then re-emission) fix the position and collapse the function? It's isn't really the same photon that is re-emitted, is it? Well, apparently it has to be a copy at the very least, but what preserves state info in the copy process?