Black Hole: Seeing Inside & Out

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Discussion Overview

The discussion revolves around the visibility of the outside universe from within a black hole, particularly focusing on the conditions inside the event horizon and the implications of gravity and light. Participants explore theoretical aspects of black holes, including time dilation and the nature of singularities.

Discussion Character

  • Exploratory
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • One participant states that it is well known that nothing can be seen inside a black hole from the outside universe due to the strong gravitational pull that prevents light from escaping.
  • Another participant suggests that visibility inside a black hole is hindered by the absence of light sources, implying that any light emitted would also be trapped by the black hole's gravity.
  • A different participant challenges the notion that one cannot see the outside universe from inside a black hole, referencing their previous posts and suggesting that under certain conditions, images may still be perceived, albeit altered by redshift effects.
  • Another participant posits that at the singularity, there is nothing to view, while also noting that extreme time dilation could render the outside universe unviewable before reaching the singularity.
  • One participant emphasizes that for an ideal Schwarzschild black hole, images can be seen, and references a specific book for further explanation on the topic.

Areas of Agreement / Disagreement

Participants express differing views on whether it is possible to see the outside universe from inside a black hole. Some argue that visibility is impossible due to gravitational effects and time dilation, while others contend that images can still be perceived under certain conditions. The discussion remains unresolved with competing perspectives.

Contextual Notes

Participants reference specific conditions such as the mass of the black hole and the nature of the singularity, indicating that assumptions about visibility may depend on these factors. The discussion includes unresolved mathematical and theoretical considerations regarding light behavior and time dilation.

RAD4921
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It is pretty well known that you cannot see inside of a black hole from the "outside" universe. It is rather obvious as to why this is because gravity is so strong that everything including light gets sucked in but I just read that you cannot see the "outside" universe from inside of a black hole (assuming one wasn't crushed first). Why is this so? Thanks RAD
 
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I think it's because you can't see anything without a light source. Because you are now where it is completely dark, the only way you could see anything is if you turned on a spotlight or something but once you did turn that on all that light wouldn't go anywhere because it would be getting sucked in too.
 
RAD4921 said:
It is pretty well known that you cannot see inside of a black hole from the "outside" universe. It is rather obvious as to why this is because gravity is so strong that everything including light gets sucked in but I just read that you cannot see the "outside" universe from inside of a black hole (assuming one wasn't crushed first). Why is this so? Thanks RAD

It's not so.

See https://www.physicsforums.com/showpost.php?p=861282&postcount=5" of mine, and other posts in the thread.

Also, if the black hole is massive enough, you won't get torn apart by tidal forces before crossing the event horizon.

Regards,
George
 
Last edited by a moderator:
Well, at the singularity (point) nothing different exists to view...it's well, singular.

Inside the event horizon, but before hitting the singularity, I suppose time dilation would be so extreme that the outside universe unviewable.
 
Phobos said:
Inside the event horizon, but before hitting the singularity, I suppose time dilation would be so extreme that the outside universe unviewable.

No, at least not for the interior of an ideal Schwarzschild black hole. As I said in my post, images are seen - some blushifted some redshifted. Also, the scare quotes I put around 'at' mean in the limit as the singularity is approached.

The book Exploring Black Holes by Taylor and Wheeler gives a readable account of how to derive just what is seen.

Regards,
George
 
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