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Oct15-10, 12:19 PM
P: 582
Why don't photons fall to earth?

Because they travel faster than the escape velocity of the earth.

A black hole, on the other hand, is a body whose escape velocity is greater than light speed, so photons always "fall back in".

How this result is calculated from General Relativity differs from that in Newtonian theory, but the essence of it is the same.