What do I see while falling into a black hole?

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Discussion Overview

The discussion revolves around the visual experiences and perceptions of an observer falling into a black hole, particularly a Schwarzschild black hole. Participants explore theoretical implications of general relativity, light behavior, and the nature of observation near the event horizon, addressing both conceptual and technical aspects of the phenomenon.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants suggest that as one falls into a black hole and looks away from it, the rest of the universe may appear to move faster, potentially infinitely fast as one crosses the event horizon.
  • Others argue that the definition of "away from it" needs clarification, and question the validity of claims made without proper references.
  • One participant describes how an observer falling from a distance would see light redshifted, while another observer close to the event horizon would experience blueshifted light from a distant observer.
  • There is mention of the ambiguity surrounding the effects of general relativity near a black hole, with some suggesting that quantum gravity effects may lead to phenomena like a "firewall" at the event horizon.
  • Some participants discuss the implications of Doppler effects and gravitational shifts on the perception of time and events as one approaches the event horizon.
  • Concerns are raised about the physical feasibility of hovering near the event horizon and the potential consequences of such actions on the observer's body.
  • There are references to media representations of falling into a black hole, noting that these simulations can vary based on the underlying theories used.
  • One participant highlights the complexity of defining what one "sees" when falling into a black hole, distinguishing between literal observations and mental models of perception.

Areas of Agreement / Disagreement

Participants express a range of views on the visual experiences of falling into a black hole, with no consensus reached on the specifics of what one would observe or the implications of those observations. The discussion remains unresolved regarding the exact nature of perception and the effects of relativistic physics in this context.

Contextual Notes

There are limitations in the discussion regarding the assumptions made about the validity of general relativity near the singularity, the definitions of terms like "finite time," and the implications of various physical effects such as redshift and blueshift. The discussion also reflects uncertainty about the nature of simultaneity in relativistic contexts.

  • #31
Arkalius said:
It seems highly doubtful to me that he's just plain wrong

Saying "time and distance swap roles" is not so much wrong as misleading, because the words "time" and "distance" in that statement do not refer to what you are intuitively thinking they refer to. They refer to coordinates, but you are intuitively thinking of them as the "time" and "distance" you experience in everyday life. The professor might simply not realize how misleading the statement is, because he understands that he's only talking about coordinates, so he does not draw the mistaken inferences from his statements that you are drawing. If so, he would not be alone; I have seen similar statements in many discussions of black holes, including some textbooks (not GR textbooks, but textbooks on other things that happen to mention black holes).
 
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  • #32
Arkalius said:
So I'd love to know what the problem is. But if you can't spare 10 minutes, perhaps someone else could.
There's a pretty good explanation here: https://arxiv.org/abs/0804.3619
The math in this paper is well beyond what belongs in a B-level thread, but Krasnikov's qualitative explanations of what it means may still be helpful. The bit about time and space switching or not switching roles is at the "remark" following equation 6; all Krasnikov needs to do is not use the same two symbols (##r## and ##t##) to label different things and the confusion disappears.
 
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