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Is it possible to slow down the speed of a light beam to a walking pace? What would it look like? Also, where does it get the extra energy to re-accelerate back to "c" when it re-enters a vacuum?

It is possible to reduce the speed of light to essentially zero, but not with traditional methods of using a material of higher index of refraction. Slowing the speed of light to near zero requires complex quantum mechanical media called Bose Einstein condensates. The mechanism involves temperatures approaching absolute zero, various laser configurations and complex instrumentation. A web search on Bose Einstein condensates + speed of light will give you as much detail and sophistication as you choose to delve into this "weird" quantum phenomenon.

Vince Calder

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