This question is similar to previously asked questions, but the responses to them are confusing and I think it may be better covered by listing out all the potential answers for clarity.
It's a simple and common question: why does light seem to travel more slowly in media which is transparent to its wavelength than it does in vacuum? I have seen responses all over the web from PhD professors at major universities whose answers are completely different. Here are all of the general categories of answers I have seen professional physicists put forth:
Light actually does move slower through transparent media. We don't really know why.
Light actually does move slower through transparent media. The reason is that light's EM effects induce nearby charged particles (electrons and nuclei) to alter the EM field with a harmonic vibration that "cancels out" some of the velocity of the light wave.
Light does not move slower. We don't know why it seems to.
Light does not move slower. It bounces around in the media which causes it to progress more slowly.
Light does not move slower. It is absorbed and emitted by electrons in the media which causes it to progress more slowly.
My thoughts on each of these:
If light actually moves slower but we haven't figured out why, I would expect it to behave relativistically in a manner similar to bradyons (particles with invariant mass which cannot reach the speed of light); but this is inconsistent with a form of energy which does not experience time. I don't see how any explanation for "slowed" light, other than 2, can be consistent.
I am currently leaning toward this answer, even though it is the rarest one I have seen. However, I don't understand the mechanics of how a light wave can be cancelled out or slowed by EM induction. My strong suspicion is that quantum effects are necessary: that is, light wouldn't be slowed at all were the environment always entangled with it (if you're one of those Copenhagen oddballs, this means if the wavefunction were continuously collapsed such that the light behaves as individual photons).
This seems pretty likely. I don't expect physicists to talk out their asses, but I have a hard time understanding why so many qualified physicists have completely different explanations for this basic principle.
This seems very unlikely to me, despite being the second-most common explanation I have found. If light were scattered, it wouldn't progress in the same direction through the media: it would disperse (to slow appreciably it would need to ricochet off of billions of atoms along the way). But we can see a beam of light refract through transparent media, and it doesn't diffuse much at all.
This is the most common explanation, yet I find it to be the least convincing! Not only do the issues from 4 apply here, but also we are talking about material which is almost completely transparent to the wavelength of light being refracted. EDIT: I previously asserted here that the slowing effect does not depend upon the frequency of light, which is incorrect. See below.
Is anybody who actually does physics for a living certain you understand this phenomenon? Or are we all spitting blind in the dark? It's very frustrating to see physicists giving incompatible explanations (with an air of certainty!) for a phenomenon known since antiquity, but I suppose it may be possible that more than one explanation is true...
EDIT: I believe I have the answer! I have answered my own question below.