4 ms·

I still don't understand why a black holes needs an inside at all. If they are equivalent to their surface then why not dispense with having an interior and jus

I still don't understand why a black holes needs an inside at all. If they are equivalent to their surface then why not dispense with having an interior and just be a surface?

twiceaday 2y ago
Why isn't the surface smaller then? Probably something inside is pushing out? It's full? Also on the way to a black hole bodies clearly have insides. Do they somehow evaporate the moment a black hole forms? Edit: My understanding is that all bodies are the size that they are because the inner/outer pressure equalizes, and this has many equilibriums based on the makeup of the body. Black holes are the ultimate degenerate last-stand where the make up is basically raw "information" which cannot be compressed any further while allowing said information to be recovered, which seems to be a fact of our universe. And it just so happens that the amount of information is proportional to the surface area of the black hole rather than its volume, which is probably a statement about how efficiently information can be compressed in our universe. One dimension is redundant?
- crackez 2y ago
  Since when is the surface of the universe that of a hypersphere?
- enkid 2y ago
  "Pressure" as a concept doesn't apply to black holes. They are the size they are because of their mass. The bigger the mass, the larger area where their gravity is so great light can't escape. Scientists model black holes as only have a mass and a spin on the inside because that's all the external universe cares about. Information being inscribed on the exterior is an artifact of tike dilating as an object approaches a black hole, iirc.
  - nvader 2y ago
    Black holes also have a charge!
    - enkid 2y ago
      Yes, that's true, thanks.
- JumpCrisscross 2y ago
  > Why isn't the surface smaller then? Probably something inside is pushing out? The surface of space doesn't require something in a higher dimension pushing it out. That such an object may appear to have internal volume from our perspective doesn't need to be any more real than the apparent depth behind a mirror.
- naasking 2y ago
  > Why isn't the surface smaller then? Probably something inside is pushing out? Hoberman spheres expand and contract via forces that act only along the structures that make up the surface, and this is a simple classical object. I don't see why a more exotic physical object like a black hole couldn't only have properties defined by its surface.
lisper 2y ago
Because if you free-fall into a black hole you can go past the event horizon.
- kelseyfrog 2y ago
  Can we? Is there a way to test this assumption? If not, then it's not science, right?
  - mr_toad 2y ago
    If you free fall into a black hole you are testing it. I don’t think that not being able to communicate your results makes it not scientific.
    - kelseyfrog 2y ago
      I think the test involves communicating your results. It's the same thing with the afterlife
      - amoss 2y ago
        Publish or perish made manifest.
      - LargoLasskhyfv 2y ago
        Maybe it could be faxed back in time through a white hole?
      - 1970-01-01 2y ago
        "Remember kids, the only difference between screwing around and science is writing it down."
    - malaya_zemlya 2y ago
      There's a theological doctrine called https://en.wikipedia.org/wiki/Eschatological_verification https://en.wikipedia.org/wiki/Eschatological_verification that claims that statements like "there's God" or "there's afterlife" are perfectly fine verifiable scientific statements, except that their verification come after death or Second Coming. Your comment reminds me of it.
bongodongobob 2y ago
A surface implies an interior, otherwise it's a just a point. A surface is a boundary, by definition there is another side, something that is being partitioned.
- kelseyfrog 2y ago
  I'm not a topological expert, but I'm pretty sure you can have a surface without an interior. A unit sphere would be a good example of a surface without an interior.
  - bongodongobob 2y ago
    ? It by definition has a radius of 1.
    - krukah 2y ago
      unit sphere != unit ball The former is the boundary, the latter is the interior + boundary. One of the great arbitrary naming conventions of math.
      - magicalhippo 2y ago
        Minor nitpick, the ball might be closed or open, depending on whether the boundary is included or not, respectively.
- JumpCrisscross 2y ago
  > surface implies an interior, otherwise it's a just a point Space-time is not Euclidean geometry under GR.
  - mr_toad 2y ago
    But it is continuous, at least until you hit or pass through the singularity.
deleted 2y ago
[deleted]
thebricklayr 2y ago
Agreed. Couldn’t black holes warp spacetime to the extent that there is no such place as “inside”? Time dilation is infinite at the event horizon, after all. As you approach the event horizon, your frame of reference slows asymptotically to match that of the black hole while the universe around you fast-forwards toward heat death. I’d expect the hawking radiation coming out at you to blue shift the closer you got until it was so bright as to be indistinguishable from a white hole. You’d never cross the event horizon; you’d be disintegrated and blasted outward into the distant future as part of that hawking radiation.
- WantonQuantum 2y ago
  The time dilation at the event horizon is infinite for an external observer. It appears that the person falling into the black hole slows down and never passes the event horizon. They redshift until you can't see them anymore. For the unfortunate person falling into the black hole, there is nothing special about the event horizon. The spacetime they experience is rotated (with respect to the external observer) in such a way that their "future" points toward the black hole. In a very real sense, for external observers there isn't really an interior of the black hole. That "inside" spacetime is warped so much that it exists more in "the future" than the present. Professor Brian Cox also says that from a string theory perspective there isn't really an inside of a black hole, it's just missing spacetime. I tried to find a reference for this but I couldn't find one. Perhaps in his book about black holes. I'm no physicist so happy to be corrected on any of the above!
  - tsunamifury 2y ago
    You know string theory is now generally considered a large scale fraud perpetrated by cox to maintain funding right?
    - WantonQuantum 2y ago
      Found Sabine Hossenfelder's HN account! I am, of course, joking but she posts this sort of easy and empty clickbait.
hoseja 2y ago
Black hole insides is another Penrose universe.
mensetmanusman 2y ago
Well stuff started on what seems like the inside, maybe space rips and everything floats to the shell?

I still don't understand why a black holes needs an inside at all. If they are equivalent to their surface then why not dispense with having an interior and just be a surface?

twiceaday 2y ago

Why isn't the surface smaller then? Probably something inside is pushing out? It's full? Also on the way to a black hole bodies clearly have insides. Do they somehow evaporate the moment a black hole forms? Edit: My understanding is that all bodies are the size that they are because the inner/outer pressure equalizes, and this has many equilibriums based on the makeup of the body. Black holes are the ultimate degenerate last-stand where the make up is basically raw "information" which cannot be compressed any further while allowing said information to be recovered, which seems to be a fact of our universe. And it just so happens that the amount of information is proportional to the surface area of the black hole rather than its volume, which is probably a statement about how efficiently information can be compressed in our universe. One dimension is redundant?

crackez 2y ago
Since when is the surface of the universe that of a hypersphere?
enkid 2y ago
"Pressure" as a concept doesn't apply to black holes. They are the size they are because of their mass. The bigger the mass, the larger area where their gravity is so great light can't escape. Scientists model black holes as only have a mass and a spin on the inside because that's all the external universe cares about. Information being inscribed on the exterior is an artifact of tike dilating as an object approaches a black hole, iirc.
- nvader 2y ago
  Black holes also have a charge!
  - enkid 2y ago
    Yes, that's true, thanks.
JumpCrisscross 2y ago
> Why isn't the surface smaller then? Probably something inside is pushing out? The surface of space doesn't require something in a higher dimension pushing it out. That such an object may appear to have internal volume from our perspective doesn't need to be any more real than the apparent depth behind a mirror.
naasking 2y ago
> Why isn't the surface smaller then? Probably something inside is pushing out? Hoberman spheres expand and contract via forces that act only along the structures that make up the surface, and this is a simple classical object. I don't see why a more exotic physical object like a black hole couldn't only have properties defined by its surface.

lisper 2y ago

Because if you free-fall into a black hole you can go past the event horizon.

kelseyfrog 2y ago
Can we? Is there a way to test this assumption? If not, then it's not science, right?
- mr_toad 2y ago
  If you free fall into a black hole you are testing it. I don’t think that not being able to communicate your results makes it not scientific.
  - kelseyfrog 2y ago
    I think the test involves communicating your results. It's the same thing with the afterlife
    - amoss 2y ago
      Publish or perish made manifest.
    - LargoLasskhyfv 2y ago
      Maybe it could be faxed back in time through a white hole?
    - 1970-01-01 2y ago
      "Remember kids, the only difference between screwing around and science is writing it down."
  - malaya_zemlya 2y ago
    There's a theological doctrine called https://en.wikipedia.org/wiki/Eschatological_verification https://en.wikipedia.org/wiki/Eschatological_verification that claims that statements like "there's God" or "there's afterlife" are perfectly fine verifiable scientific statements, except that their verification come after death or Second Coming. Your comment reminds me of it.

bongodongobob 2y ago

A surface implies an interior, otherwise it's a just a point. A surface is a boundary, by definition there is another side, something that is being partitioned.

kelseyfrog 2y ago
I'm not a topological expert, but I'm pretty sure you can have a surface without an interior. A unit sphere would be a good example of a surface without an interior.
- bongodongobob 2y ago
  ? It by definition has a radius of 1.
  - krukah 2y ago
    unit sphere != unit ball The former is the boundary, the latter is the interior + boundary. One of the great arbitrary naming conventions of math.
    - magicalhippo 2y ago
      Minor nitpick, the ball might be closed or open, depending on whether the boundary is included or not, respectively.
JumpCrisscross 2y ago
> surface implies an interior, otherwise it's a just a point Space-time is not Euclidean geometry under GR.
- mr_toad 2y ago
  But it is continuous, at least until you hit or pass through the singularity.

deleted 2y ago

[deleted]

thebricklayr 2y ago

Agreed. Couldn’t black holes warp spacetime to the extent that there is no such place as “inside”? Time dilation is infinite at the event horizon, after all. As you approach the event horizon, your frame of reference slows asymptotically to match that of the black hole while the universe around you fast-forwards toward heat death. I’d expect the hawking radiation coming out at you to blue shift the closer you got until it was so bright as to be indistinguishable from a white hole. You’d never cross the event horizon; you’d be disintegrated and blasted outward into the distant future as part of that hawking radiation.

WantonQuantum 2y ago
The time dilation at the event horizon is infinite for an external observer. It appears that the person falling into the black hole slows down and never passes the event horizon. They redshift until you can't see them anymore. For the unfortunate person falling into the black hole, there is nothing special about the event horizon. The spacetime they experience is rotated (with respect to the external observer) in such a way that their "future" points toward the black hole. In a very real sense, for external observers there isn't really an interior of the black hole. That "inside" spacetime is warped so much that it exists more in "the future" than the present. Professor Brian Cox also says that from a string theory perspective there isn't really an inside of a black hole, it's just missing spacetime. I tried to find a reference for this but I couldn't find one. Perhaps in his book about black holes. I'm no physicist so happy to be corrected on any of the above!
- tsunamifury 2y ago
  You know string theory is now generally considered a large scale fraud perpetrated by cox to maintain funding right?
  - WantonQuantum 2y ago
    Found Sabine Hossenfelder's HN account! I am, of course, joking but she posts this sort of easy and empty clickbait.

hoseja 2y ago

Black hole insides is another Penrose universe.

mensetmanusman 2y ago

Well stuff started on what seems like the inside, maybe space rips and everything floats to the shell?