Unpredictable Outcomes: What Happens When Falling into a Black Hole?

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Discussion Overview

The discussion revolves around the experiences and observations of an observer falling into a black hole, particularly focusing on what they would see as they approach and cross the event horizon. Participants explore theoretical implications of general relativity, the nature of spacetime near black holes, and the effects of tidal forces on the observer's experience.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation

Main Points Raised

  • Some participants propose that an observer falling into a black hole would see the rest of the universe progress rapidly, while others challenge this notion, suggesting it is not an accurate description of the experience.
  • There is a discussion about whether crossing the event horizon would affect cognitive functions, with some arguing that as long as tidal forces are not significant, the observer would not notice anything unusual.
  • One participant mentions the concept of a "wall of fire" that could be encountered, contrasting it with the idea that an observer might not notice anything if they do not look outside.
  • The relevance of tidal forces is emphasized, with some suggesting that if these forces become significant, they would be noticeable to the observer.
  • There is mention of the uncertainty surrounding black hole behavior, with one participant noting that mathematical calculations may not fully capture the reality of the situation.
  • Another participant raises the possibility that black holes can "spit out" objects, referencing observations of stars, but this claim is met with a request for further evidence.

Areas of Agreement / Disagreement

Participants express a mix of agreement and disagreement regarding the implications of falling into a black hole. While some aspects are clarified, such as the role of tidal forces, the overall experience of the observer and the nature of spacetime remain contested and unresolved.

Contextual Notes

Discussions include assumptions about the observer's experience and the conditions under which they might notice spacetime distortions. The conversation reflects varying interpretations of general relativity and the complexities involved in understanding black hole physics.

Who May Find This Useful

This discussion may be of interest to those studying general relativity, astrophysics, or anyone curious about the theoretical implications of black holes and the nature of spacetime.

Grogbor
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I was watching a video about how an observer outside a black hole would watch someone slow to a halt at the event horizon and I don't question it, as that makes sense.

My first question to the Astrophysicists out there is what the observer falling into the black hole would see. It would make sense to me that they would observe the rest of the universe progress through the entirety of its existence.

Does this make sense?

My second question is about what people say would happen for a supermassive black hole, that it would be pleasant when crossing the event horizon. If the event horizon means that no world lines can travel away from the black hole, doesn't that imply that, once crossed, a person could no longer think, as impulses in the brain travel slower than light and cannot travel from place to place, but only towards the center of the black hole? Would this also apply when getting close to the black hole (i.e. within a few kilometers of the black hole's event horizon)?

Thanks for your time!
 
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Grogbor said:
My first question to the Astrophysicists out there is what the observer falling into the black hole would see. It would make sense to me that they would observe the rest of the universe progress through the entirety of its existence.

Does this make sense?
No, it is not an accurate description of what happens. There are several threads at PF about this which you can find by the search function or by looking at the similar discussions below.

Grogbor said:
If the event horizon means that no world lines can travel away from the black hole, doesn't that imply that, once crossed, a person could no longer think, as impulses in the brain travel slower than light and cannot travel from place to place, but only towards the center of the black hole?
No, this is also not accurate. As long as the observer is not subjected to large tidal forces, it will not notice anything strange. The local speed of light is also the same as everywhere else and the point of light being unable to escape is based on the geometry of space-time, not on the local speed of light changing.
 
.Scott said:
This is certain one of the top ten general relativity questions.
Have you checked out this thread: https://www.physicsforums.com/threads/falling-into-black-hole.463880/?

Thanks very much for the redirect, I'll check that out.

Orodruin said:
No, it is not an accurate description of what happens. There are several threads at PF about this which you can find by the search function or by looking at the similar discussions below.

No, this is also not accurate. As long as the observer is not subjected to large tidal forces, it will not notice anything strange. The local speed of light is also the same as everywhere else and the point of light being unable to escape is based on the geometry of space-time, not on the local speed of light changing.

I believe I'm starting to understand. Does this imply that the local spacetime distortions are not noticeable to the infalling observer?
 
Grogbor said:
I believe I'm starting to understand. Does this imply that the local spacetime distortions are not noticeable to the infalling observer?
I avoided that question because there are some that think that you might run into a "wall of fire" (http://arxiv.org/abs/1207.3123). But the older notion (and the one I still subscribe to) is that, if the observer doesn't look out the window, he will notice nothing - but that will be a very short-lived experience.
 
Grogbor said:
Does this imply that the local spacetime distortions are not noticeable to the infalling observer?

This depends on how large the neighbourhood of the observer which can be considered "local" is. If tidal effects become relevant over in his local neighbourhood, they will most certainly be noticeable.
 
We could currently be falling through the horizon of some very large, yet to be formed black hole...and we are still able to think right now. As commented already, it is really the tidal forces that are important
 
It's a very interesting question because no one really knows the answer. We can rely on the mathematical calculations but can't be sure that the laws work the same way we think they should. Anyway, according to the latest observations, a black hole:nb) can simply spit you out (as it is sometimes the case of swallowed stars) and you won't see a thing.
 
HunterThomson said:
It's a very interesting question because no one really knows the answer. We can rely on the mathematical calculations but can't be sure that the laws work the same way we think they should. Anyway, according to the latest observations, a black hole:nb) can simply spit you out (as it is sometimes the case of swallowed stars) and you won't see a thing.

Could you provide a reference for your "simply spit you out" remarks?
 

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