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The Question

(Submitted October 24, 2001)

Why do theories say that time will slow down on the event horizon and then go backwards? Please explain in laymans terms.

The Answer

Time does not slow down and then go backwards at a black hole's event horizon, but a lot of strange stuff does occur.

If you (in a space ship, for example) were to approach the event horizon and cross it, to a person watching you from a great distance it would look like you moved slower and slower as you got closer and closer to the horizon. To them it would look like you never quite reached the horizon. But this is an illusion caused by the fact that the light you emit from your space ship is taking longer and longer to reach the outside observer. This is due to the black hole's immense gravity. From your own point of view, you reach the horizon and cross it, with nothing special happening at the boundary. But of course, the gravitational forces of the black hole will crush you do death sooner or later!

For more on black holes, check out this website:
http://cosmology.berkeley.edu/Education/BHfaq.html

This website also has some information on black holes:
http://math.ucr.edu/home/baez/physics/

Amy C. Fredericks and Mike Loewenstein for Ask an Astrophysicist

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