Thursday 27 August 2015

general relativity - How does light behave within a black hole's event horizon?


If the event horizon of a black hole is the distance from the center from within which light cannot escape, imagine a person with a flashlight falls into the black hole.


He points his flashlight in a precisely radial direction and turns it on. Now there is a light ray moving outward at the speed of light. If it now cannot move in an arc, but rather is constrained to radial motion, it must, at some point before the horizon, switch directions and fall back into the black hole.


If the speed of light is constant, how does it suddenly change directions, without either decelerating, or requiring an infinite amount of energy?




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