Falling into a Black Hole

In summary, the conversation discusses questions about what someone falling into a black hole would see and experience. It is mentioned that the observer would not notice anything strange as long as they are not subjected to large tidal forces. Some theories suggest that the observer may experience a "wall of fire" upon crossing the event horizon, but this is still a topic of debate. It is also mentioned that the local spacetime distortions may not be noticeable to the infalling observer, but this depends on the size of their local neighborhood. The conversation ends with a comment about the latest observations of black holes being able to "spit out" objects that were previously swallowed.
  • #1
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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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  • #3
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.
 
  • #4
.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?
 
  • #5
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.
 
  • #6
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.
 
  • #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
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?
 

1. What happens when you fall into a black hole?

When you fall into a black hole, you will experience extreme gravitational forces that will stretch your body and eventually tear you apart. As you approach the event horizon, the point of no return, you will also experience time dilation, meaning time will pass slower for you compared to someone observing you from outside the black hole.

2. Can anything escape from a black hole?

According to current scientific understanding, nothing can escape from a black hole once it has passed the event horizon. This includes light, making black holes appear completely black to outside observers.

3. Can black holes be seen or detected?

Black holes themselves cannot be seen, as they do not emit light. However, we can detect their presence by observing their effects on surrounding matter, such as the accretion disk of gas and dust that forms as material falls into the black hole.

4. What is the size of a black hole?

The size of a black hole is determined by its event horizon, which is directly related to its mass. The more massive a black hole is, the larger its event horizon will be. For example, the event horizon of a black hole with the mass of the sun would be about 3 kilometers in diameter.

5. Are black holes dangerous to Earth?

Black holes that are far enough away from Earth pose no threat to us. However, if a black hole were to enter our solar system, its gravitational pull could disrupt the orbits of planets and potentially cause catastrophic events. Luckily, the nearest known black hole is about 1,600 light years away.

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