I have a simple question to which, I assume, the answer will be quite complicated. I asked my physics teacher this question and all he would say was, "It is known." So without beating me to death with physics can anyone tell me why waves diffract? For instance, electron diffraction around a nucleus. I also would like to know why things refract. I have learnt how, when a photon comes into contact with an atom, electrons are promoted to higher energy levels if the photon is of a high enough energy. But this is the only way in which I know of how em-radiation can interact with matter. Once again I asked my physics teacher and all he would say is that, "In the prescence of certain magnetic fields, light can interact with matter," or words to that effect, (I can't remember exactly what he said, or even if it was magnetic fields that he refered to). Another little side-bar, if a ray of light hits a perspex block at less than the criticle angle, it enters the block and refracts. If a ray of light hits a perspex block at greater than the criticle angle, it reflects. But if a ray of light hits a perspex block AT the criticle angle, it travels along the edge of the block, but is the ray of light inside or outside the block? [?] Oh yeah, that's another one. Why does em-radiation reflect? I suppose this will be intimately related to refraction but it would be nice to know.