So why do different media slow light down?

[Tyro]

As I see it, which is probably wrong, the speed of light changes in different media because of absorption and re-emission of the photons. This sequence of events takes longer than light just passing straight through a vacuo, which means that the average velocity will be lower.

I have a feeling, though, that this is wrong. If absorption and re-emission is what happened even in transparent substances, you would see a very fuzzy picture through them because re-emission has no directional preference - the image will be completely dispersed (which it isn't).

So why do different media slow light down?

 

[Tyger]

Feynman to the rescue again here too.

His little book QED gives a good description of this subject.

 

[russ_watters]

Originally posted by Tyro
As I see it, which is probably wrong, the speed of light changes in different media because of absorption and re-emission of the photons. This sequence of events takes longer than light just passing straight through a vacuo, which means that the average velocity will be lower.

No, you're wrong - you're right!

But the reason you are wrong is that reflection and refraction CAN and does often happen linearly - there is a directional preference depending on the medium.