I'm a materials engineering junior-to-be(yay summer), and like most material scientists i just kind of assume things I dont really understand when it comes to physics =P But I was pondering about refractive indexes today and... Well, WHY does light slow down in a medium? The refractive index of glasses varies with the polorizability of the ions or their electron density so this leads me to believe that that somehow the light interacts with the electrons. I don't know how it would classically interact with the electrons without transfusing energy to them (light doesn't lose energy as it transmits through materials, so it would obviously not) so i was thinking quantum mechanically - which I know almost zippo about (next to the basics they teach you in like, chem in high school. None of that superpositions of states or anything). I know the light interacts with the medium when the energy states match (absorption due to phonons, transitions of electrons to higher orbitals, etc.) but when it doesn't do that - why does it slow down/bend? Also, i find myself taking things that i always took for fact and now i don't see how they work: How in the world does an electromagnetic wave - an electric field and a magnetic field flying through space - NOT effect a charged particle(electron/proton) classically? Obviously it doesn't but why not? If I shove any other kind of magnetic field next to an electron it reacts, any kind of electric field an electron gets entangled with they react - why not EM waves? Quantum states don't match? But why can't it just give the electron kinetic energy - have an light wave fly near an electron and then the electron speeds off away from the light? But if the mag/elec fields are oscillating pos-neg-pos-neg-pos why doesn't the electron oscillate with it; attract-repel-attract-repel-attract? That would obviously transfer energy, but we don't see degradation of light energy in such a manner so why doesn't it happen? >.> <.<, I'll stop rambling now. There are probably really simple explanations to these and I'm just overlooking them as usual =P Help? - that is if you can understand my babble.