Changing Media and Speed of Light
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.
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Update: June 2012