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Black hole question

  1. Jul 1, 2012 #1


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    I have red that as an object approaches a black hole, to an observer the object never appears to pass the event horizon because of time dilation.

    If so why does the hole appear black, wouldn't the same thing happen to the light, and wouldn't it spread over the surface of the black hole, making it visible?
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  3. Jul 1, 2012 #2


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    what you are talking about happens because the light is red-shifted and yes, the light coming in DOES get affected the same way ... it gets red-shifted out of existance for all practical purposes.
  4. Jul 1, 2012 #3


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    The incoming light does get redshifted, but, not to the extent of the outgoing light.
  5. Jul 2, 2012 #4


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    Light emitted from closer and closer to the event horizon does indeed get heavily redshifted. Light that comes from somewhere else and doesn't enter the event horizon is warped around the black hole but does not have a net redshift, as it was first blueshifted when it approached the black hole and then red shifted on the way out. One effect is that if you were close to a black hole you would see the background being seriously warped near it.
  6. Jul 2, 2012 #5
    That is a view for a static [accelerating] observer well outside the horizon in Schwarzschild coordinates; for a free falling observer, time passes normally and the blackness approaches as you would expect. In ther coordinate systems, effects are different.

    A crude analogy in everday life might be "Are distant objects really smaller than nearby objects." Or is it an 'illusion'?? Which is 'real'???
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