What do I see while falling into a black hole?

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SUMMARY

When falling into a Schwarzschild black hole, an observer looking away from the black hole perceives the universe outside as moving increasingly faster, culminating in an infinite speed as they cross the event horizon. This phenomenon is due to the effects of gravitational blueshift and Doppler redshift, which alter the frequency of light received by the observer. Observers at different distances from the black hole experience varying shifts in light, with those closer to the event horizon seeing redshifted light from distant stars. The calculations using Painleve-Gullstrand coordinates confirm that general relativity remains valid even at the event horizon, challenging misconceptions about catastrophic experiences upon crossing it.

PREREQUISITES
  • Understanding of Schwarzschild black holes
  • Familiarity with gravitational blueshift and Doppler redshift
  • Knowledge of general relativity principles
  • Ability to interpret Painleve-Gullstrand coordinates
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  • Explore the implications of gravitational time dilation near black holes
  • Study the effects of light redshift and blueshift in astrophysical contexts
  • Investigate the concept of event horizons in different types of black holes
  • Learn about the mathematical formulations of general relativity related to black holes
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Astronomers, physicists, and students of astrophysics interested in the behavior of light and time near black holes, as well as those exploring the implications of general relativity in extreme gravitational fields.

  • #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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