Falling into a Black Hole

  • #1
2
0
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!
 

Answers and Replies

  • #3
Orodruin
Staff Emeritus
Science Advisor
Homework Helper
Insights Author
Gold Member
17,167
6,973
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.

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.
 
  • #4
2
0
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.

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?
 
  • #5
.Scott
Homework Helper
2,731
1,030
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.
 
  • #6
Orodruin
Staff Emeritus
Science Advisor
Homework Helper
Insights Author
Gold Member
17,167
6,973
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.
 
  • #7
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
 
  • #8
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.
 
  • #9
pervect
Staff Emeritus
Science Advisor
Insights Author
10,026
1,203
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?
 

Related Threads on Falling into a Black Hole

  • Last Post
Replies
3
Views
754
  • Last Post
Replies
24
Views
5K
  • Last Post
Replies
0
Views
2K
  • Last Post
Replies
6
Views
3K
  • Last Post
Replies
6
Views
2K
  • Last Post
Replies
17
Views
4K
  • Last Post
Replies
20
Views
4K
  • Last Post
Replies
21
Views
5K
  • Last Post
4
Replies
77
Views
15K
  • Last Post
Replies
22
Views
5K
Top