Quote:
Originally Posted by absael
I saw a post here in which the poster seemed to be saying that the speed of light is less when traveling through matter. I have also seen numerous Internet sites that seem to say this. My understanding is that the speed of light is constant, but that it propagates through matter at different rates as atoms absorb and re-emit photons. This seems to me to be an important distinction. Which is correct?
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The speed of light is constant in a particular medium. So yes, the speed of light is different in different media. But it will always be the same speed in the same medium. So the speed of light in water (at 1 atmosphere, 20 deg Celsius) , for example, will always be the same in any water in the same environment.
However, light has a maximum speed, the speed of light in a vacuum. Nothing travels faster than this upper limit.
They've conducted experiments with exotic materials and gasses in which they've slowed down the speed of light in that medium to several miles per hour!
Rob