What I thought would be a boring post on EM boundary conditions a few days ago has turned into something interesting. Jonah Miller replied back to the post and made a comment that ultimately led to the Abraham-Minkowski controversy on how to interpret the momentum of a photon in a piece of material. Apparently this debate has progressed fora little bit over 100 y ears with the form of the momentum equation in a material proposed by Max Abraham apparently conflicting with the one proposed by Hermann Minkowski of Minkowski metric fame where n is the index of refraction for the material, h is Planck's constant, nu is the frequency of the light, and c is the speed of light. The controversy even led to people studying whether or not the discrepancy might be used as the basis for a reactionless drive with the Air Force and NASA purportedly getting in on the game according to Wikipedia. It turns out that the answer in all likelihood is that everyo...