6 ms·

Basing this on personal hunch instead of any theoretical hard standing whatsoever I think black holes are really just the event horizon, there's nothing 'inside

Basing this on personal hunch instead of any theoretical hard standing whatsoever I think black holes are really just the event horizon, there's nothing 'inside' the event horizon. I believe that the collapse into a 'black hole' 'stops' at the moment that space-time curvature creates a sphere of space-time that geometrically appears to us 'outsiders' as the surface of a sphere or a shell - ergo the event horizon. That is, I believe that there is _nothing_ inside the event horizon (literally nothing, no space-time, no anything), the event horizon is just the region of space-time occupying the surface of a shell inside which there is NOTHING. I don't believe you fall 'through' the event horizon, I think that the matter that would otherwise make up the singularity at the centre of the black hole is smeared over this surface/event-horizon region. There are problems with this idea, but those are somewhat related to the fact we believe matter becomes infinitely dense (why wouldn't material on the surface of the sphere collapse to smaller spheres/event-horizons of their own) But infinite density is clearly not a 'proven' theory, however widely it's postulated - so we clearly don't understand if that is even a physical possibility. I've not seen anything concrete that says you can't model a black-hole as a shell of mass. As I understand it, to an outside observer a shell behaves gravitationally identically to a point mass at the centre of such a shell would. Of course, I'm no doubt very wrong, but whenever I've mentioned this to anyone, no one has really come up with anything to say it absolutely isn't possible, not without holding on to other things we 'think' we know like matter 'should' continue to collapse to infinite density once past some arbitrary point. Something I'm not convinced is true.

privong 11y ago
> I've not seen anything concrete that says you can't model a black-hole as a shell of mass. As I understand it, to an outside observer a shell behaves gravitationally identically to a point mass at the centre of such a shell would. > Of course, I'm no doubt very wrong, but whenever I've mentioned this to anyone, no one has really come up with anything to say it absolutely isn't possible, not without holding on to other things we 'think' we know like matter 'should' continue to collapse to infinite density once past some arbitrary point. Something I'm not convinced is true. Sure, you can model the external gravitational field as a shell of mass (interior to the event horizon), but they you have to explain why the mass is in a shell, rather than collapsing in on itself. If black holes form as the remnant of the cores of massive stars, then there's no shell configuration to start out with, so now you also have to explain why a shell forms in addition to it is maintained. So, while the shell model may be consistent with the external gravitational field, it seems to be constructed in an ad hoc fashion. Also, not everyone thinks matter should collapse to infinite density, e.g., [0]. I don't have enough domain knowledge to say how reasonable that particular model is. But "collapsing to infinite density" is a simple explanation for non-experts, but I don't think physicists are comfortable with it as an actual interpretation. The more common interpretation is that the laws of physics we have do not apply in such situations, and we need an understanding of quantum gravity to say what happens at the center of a black hole. [0] http://arxiv.org/abs/gr-qc/0506111 http://arxiv.org/abs/gr-qc/0506111
- keenerd 11y ago
  > but then you have to explain why the mass is in a shell, rather than collapsing in on itself. That is an easy one. It is the only "stable" configuration given two pieces of information: 1) The force of (and therefor effects of) gravity of a sphere is maximum on the surface and tapers to zero at the center. 2) Time (and therefor motion) all but stops at when the force of gravity reaches black-hole proportions. So the center becomes an unstable region of low density and rapid time/motion, and the surface becomes a stable region of treacle-time. A hollow sphere would be the result. That said it is almost certainly wrong because it is sufficiently simple that every pop-culture astrophysicist would have written about it, and none have.
  - akiselev 11y ago
    The net force on a particle due to gravity tapers towards the center but the pull of gravity on the surrounding particles accumulates into pressure preventing any lower density from forming on the interior unless there is another force like fusion providing outward pressure. Since black holes form after gravitational collapse that is no longer possible. The only natural equivalent I can think of would be rotational vorteces (tornadoes) but the "shell" would be two dimensional and such a system requires two fluids with different properties, which couldn't exist in the black hole.
    - keenerd 11y ago
      > the pull of gravity on the surrounding particles accumulates into pressure preventing any lower density from forming on the interior unless there is another force ... providing outward pressure. (Keep in mind I don't believe this, it is just fun to argue cute ideas from basic principles.) In this case the secondary force would be time dilation. Assuming that black holes have finite density, there must be a second event horizon inside the body. Just as a particle can't escape the surface going upwards, particles inside the black hole would not be able to escape downwards, if between the two horizons. While the force of gravity would still pull particles towards the center and away from the interior horizon, any brownian motion away from the center is self-reinforcing since the particle moves towards a region of greater time dilation. There would be an intermediary unstable stage like a nut rattling around inside a shell, but the slightest instability would start the core oscillating, and each time it brushes the shell it loses a bit more mass. When matter approaches an event horizon it tends to release a lot of energy, repeatedly breaking up (or boiling off) the core and launching bits of it into the shell. This provides a another source of outward pressure. Reiterating: this is likely complete poppycock. edit: Ah, I see the snag. There isn't a second event horizon inside the black hole. Just because opposing gravitational forces cancel each other out in the center (and space is flat there) does not mean time is any less distorted by all the surrounding mass.
danbruc 11y ago
A few comments. I doubt that many or even any serious physicist imagine something of infinite density inside a black hole, infinities are just the way our theories tell us that we don't understand things well enough and got the math wrong. The event horizon can be a very ordinary place with almost flat space and no strong gravitational forces. You can probably cross the event horizon of a large black hole without even noticing what you just did and that you are doomed. So imagining that the event horizon is kind of a wall with nothing behind the wall most likely does not work. Lastly the singularity is not a place but a time, the common pictures of black holes are highly inadequate to think about black holes.
- guard-of-terra 11y ago
  Event horizon is an ordinary place that happens to be bombarded by high energy particles coming from the whole galaxy in great numbers. I think you'll note.
  - danbruc 11y ago
    Black holes are not active all the time, after cleaning out the surrounding space they can go through extended periods in which they are not aggregating more mass. I am not even sure if you should expect particles with high energy rushing in. Why not gas clouds with densities of a few atoms per cubic meter drifting into the black hole with modest velocity? If I remember correctly you can even be inside the event horizon before the black hole actually formed, I would definitely not expect high energy particles in such an scenario.
    - guard-of-terra 11y ago
      When you approach event horizon you witness the galaxy age and die, and also get multiple billion year load of heavy particles, possibly even blueshifted thermal photons.
      - danbruc 11y ago
        Nothing special happens when you approach or cross the event horizon. If you look back, even from inside the event horizon, everything looks normal to you, at least until you are close enough to the singularity so that the curvature becomes significant. Only observers outside of the black hole see the event horizon as a special place. For a pretty accessible introduction including a discussion of falling into a black hole see for example [1]. [1] http://theoreticalminimum.com/courses/general-relativity/2012/fall http://theoreticalminimum.com/courses/general-relativity/201...
guard-of-terra 11y ago
I've come to same conclusions and even got a minimal model. Imagine two Planck singularities falling toward each other. For an external observer, they'll stop eventually due to time dilution. What's between them now?
spdustin 11y ago
Why wouldn't the "filling" of that black hole shell be the pressure of the so-called dark energy that's inflating the universe itself? Maybe it's the leakage of these additional sources of dark energy that's fueling the increasing expansion of space-time. Armchair physics here, but it's fascinating to ponder.

privong 11y ago

> I've not seen anything concrete that says you can't model a black-hole as a shell of mass. As I understand it, to an outside observer a shell behaves gravitationally identically to a point mass at the centre of such a shell would. > Of course, I'm no doubt very wrong, but whenever I've mentioned this to anyone, no one has really come up with anything to say it absolutely isn't possible, not without holding on to other things we 'think' we know like matter 'should' continue to collapse to infinite density once past some arbitrary point. Something I'm not convinced is true. Sure, you can model the external gravitational field as a shell of mass (interior to the event horizon), but they you have to explain why the mass is in a shell, rather than collapsing in on itself. If black holes form as the remnant of the cores of massive stars, then there's no shell configuration to start out with, so now you also have to explain why a shell forms in addition to it is maintained. So, while the shell model may be consistent with the external gravitational field, it seems to be constructed in an ad hoc fashion. Also, not everyone thinks matter should collapse to infinite density, e.g., [0]. I don't have enough domain knowledge to say how reasonable that particular model is. But "collapsing to infinite density" is a simple explanation for non-experts, but I don't think physicists are comfortable with it as an actual interpretation. The more common interpretation is that the laws of physics we have do not apply in such situations, and we need an understanding of quantum gravity to say what happens at the center of a black hole. [0] http://arxiv.org/abs/gr-qc/0506111 http://arxiv.org/abs/gr-qc/0506111

keenerd 11y ago
> but then you have to explain why the mass is in a shell, rather than collapsing in on itself. That is an easy one. It is the only "stable" configuration given two pieces of information: 1) The force of (and therefor effects of) gravity of a sphere is maximum on the surface and tapers to zero at the center. 2) Time (and therefor motion) all but stops at when the force of gravity reaches black-hole proportions. So the center becomes an unstable region of low density and rapid time/motion, and the surface becomes a stable region of treacle-time. A hollow sphere would be the result. That said it is almost certainly wrong because it is sufficiently simple that every pop-culture astrophysicist would have written about it, and none have.
- akiselev 11y ago
  The net force on a particle due to gravity tapers towards the center but the pull of gravity on the surrounding particles accumulates into pressure preventing any lower density from forming on the interior unless there is another force like fusion providing outward pressure. Since black holes form after gravitational collapse that is no longer possible. The only natural equivalent I can think of would be rotational vorteces (tornadoes) but the "shell" would be two dimensional and such a system requires two fluids with different properties, which couldn't exist in the black hole.
  - keenerd 11y ago
    > the pull of gravity on the surrounding particles accumulates into pressure preventing any lower density from forming on the interior unless there is another force ... providing outward pressure. (Keep in mind I don't believe this, it is just fun to argue cute ideas from basic principles.) In this case the secondary force would be time dilation. Assuming that black holes have finite density, there must be a second event horizon inside the body. Just as a particle can't escape the surface going upwards, particles inside the black hole would not be able to escape downwards, if between the two horizons. While the force of gravity would still pull particles towards the center and away from the interior horizon, any brownian motion away from the center is self-reinforcing since the particle moves towards a region of greater time dilation. There would be an intermediary unstable stage like a nut rattling around inside a shell, but the slightest instability would start the core oscillating, and each time it brushes the shell it loses a bit more mass. When matter approaches an event horizon it tends to release a lot of energy, repeatedly breaking up (or boiling off) the core and launching bits of it into the shell. This provides a another source of outward pressure. Reiterating: this is likely complete poppycock. edit: Ah, I see the snag. There isn't a second event horizon inside the black hole. Just because opposing gravitational forces cancel each other out in the center (and space is flat there) does not mean time is any less distorted by all the surrounding mass.

danbruc 11y ago

A few comments. I doubt that many or even any serious physicist imagine something of infinite density inside a black hole, infinities are just the way our theories tell us that we don't understand things well enough and got the math wrong. The event horizon can be a very ordinary place with almost flat space and no strong gravitational forces. You can probably cross the event horizon of a large black hole without even noticing what you just did and that you are doomed. So imagining that the event horizon is kind of a wall with nothing behind the wall most likely does not work. Lastly the singularity is not a place but a time, the common pictures of black holes are highly inadequate to think about black holes.

guard-of-terra 11y ago
Event horizon is an ordinary place that happens to be bombarded by high energy particles coming from the whole galaxy in great numbers. I think you'll note.
- danbruc 11y ago
  Black holes are not active all the time, after cleaning out the surrounding space they can go through extended periods in which they are not aggregating more mass. I am not even sure if you should expect particles with high energy rushing in. Why not gas clouds with densities of a few atoms per cubic meter drifting into the black hole with modest velocity? If I remember correctly you can even be inside the event horizon before the black hole actually formed, I would definitely not expect high energy particles in such an scenario.
  - guard-of-terra 11y ago
    When you approach event horizon you witness the galaxy age and die, and also get multiple billion year load of heavy particles, possibly even blueshifted thermal photons.
    - danbruc 11y ago
      Nothing special happens when you approach or cross the event horizon. If you look back, even from inside the event horizon, everything looks normal to you, at least until you are close enough to the singularity so that the curvature becomes significant. Only observers outside of the black hole see the event horizon as a special place. For a pretty accessible introduction including a discussion of falling into a black hole see for example [1]. [1] http://theoreticalminimum.com/courses/general-relativity/2012/fall http://theoreticalminimum.com/courses/general-relativity/201...

guard-of-terra 11y ago

I've come to same conclusions and even got a minimal model. Imagine two Planck singularities falling toward each other. For an external observer, they'll stop eventually due to time dilution. What's between them now?

spdustin 11y ago

Why wouldn't the "filling" of that black hole shell be the pressure of the so-called dark energy that's inflating the universe itself? Maybe it's the leakage of these additional sources of dark energy that's fueling the increasing expansion of space-time. Armchair physics here, but it's fascinating to ponder.