Object Approaching Black Hole: Time Dilation & Visibility

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Discussion Overview

The discussion revolves around the phenomenon of time dilation as objects approach a black hole, specifically addressing why black holes appear black despite the effects of time dilation on light and objects near the event horizon. The scope includes theoretical considerations and conceptual clarifications related to black holes and light behavior.

Discussion Character

  • Exploratory
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants propose that as an object approaches a black hole, it never appears to cross the event horizon due to time dilation, raising questions about the visibility of the black hole itself.
  • Others argue that while light emitted from near the event horizon is heavily redshifted, light that comes from farther away may be warped but does not necessarily experience a net redshift.
  • A participant mentions that the perception of time and the behavior of light can differ depending on the observer's frame of reference, such as a static observer versus a free-falling observer.
  • There is a suggestion that the effects observed near a black hole could be analogous to everyday perceptions of distance and size, questioning the nature of reality in these contexts.

Areas of Agreement / Disagreement

Participants express multiple competing views regarding the behavior of light near black holes and the implications of time dilation, indicating that the discussion remains unresolved.

Contextual Notes

Limitations include varying interpretations of light behavior based on different coordinate systems and the effects of gravitational fields on time perception, which remain unresolved in the discussion.

FOIWATER
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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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FOIWATER said:
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?

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 existence for all practical purposes.
 
The incoming light does get redshifted, but, not to the extent of the outgoing light.
 
FOIWATER said:
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?

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.
 
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.

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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