In the famous two-split experiment in your freshman college class, you learn that shining a light at a wall with two narrow slits causes a diffraction pattern. Something that's always bothered me is in these ideal setups, we always assume the wall is a continuous barrier to the light. But the barrier is made up of a lattice of atoms. The interaction is never as simple as the idealized experiment. I'm curious as to what's actually going on between the light and the wall.