True enough that the speed of light differs according to the medium it is in, somewhat slower in air than in a vacuum, somewhat slower yet in water, etc. But in a medium like copper, I don't think the question is how fast so much as it is how far, i.e. how far does light penetrate into such a substance. Not very far, I'm sure.
The billiard balls is a good analogy - fill a 2" conduit with billiard balls 'till it's full. Then push another one in at one end, and one will be pushed out the other end at the same time, making it seem like extremely high speed (which it's not).
I'll get in a longer post tomorrow.
Radar
