the speed of light

Here's another way of thinking about it...

Take 1 photon of light and 1 particle of matter.

Light traveling in a straight line:

1 2 3 4 5 6 7

Light traveling through a medium and interacting with a particle:

. . . 4 5 6
1 2 3 X 7 8 9
. . . 4 5 6

For the first example it takes 7 ticks and in the second 9 ticks. It seems slower because acting as a wave it has to go around the particle and this would take a certain amount of time.

Hmm...

I think the answer is in the interaction between the light and the electrons. When the wavefront strikes the material it's travelling through, the electrons will absorb some of the wavelets. And when the excited electron emits a photon, it will be in a different phase. There are quite a few atoms in any piece of material, so it has the accumulative effect of slowing down (or in the case of plasmas, speeding up) the wavefront, even though the light never stops travelling at 'c'.

In short: Light never stops travelling at speed 'c'. It's all about the change in phase. Analogies with soundwaves aren't all that helpful.

Morbert has essentially the right answer. A photon always travels at 'c'. When it interacts with an electron, there is a little dance done (nobody knows what happens), which takes a finite amount of time, after which the electron goes on it's way again at 'c'. The time taken for the dance results in a change in phase of the wave front (equivalent to refractive index of the medium) and an effective slowing of the wave front through the medium.

Interesting,
This means that the lenses refractive index is dictated by the density?, I'd never thought of it like that before.
Does anyone have an equation for this ??

I always knew C was Constant

Intresting alright... did a quick google search which brought up some Wikipedia entries (probably should of done this when the tread was originally started, but hey it's kinda fun to think about it before looking it up)

en.wikipedia.org/wiki/Speed_of_light

en.wikipedia.org/wiki/Refractive_index