Time, Gravity

freyar said:

What you say is true. The thing is that getting infalling stuff into the horizon in finite time isn't considered an issue, and I've never heard any of the "big thinkers" about black holes, Hawking radiation, etc, mention any worries about needing to tunnel into a black hole. So I just wouldn't want to say that tunnelling in is in any way a consensus view.

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Well, most discussion of black holes addresses them as steady-state objects. But when you start talking about growth of a hole (say, as a possible route to formation of supermassive holes) the issue comes up. The two basic models I have heard of are: 1)vaguely invoke QM tunneling to get the stuff to jump the gap, and 2) assume the in-falling matter accrues in a shell or ring to such density in finite time that it undergoes gravitational collapse itself. At the time, the latter was deemed problematic, as you'd be expecting the equivalent of yet another kind of supernova event that wasn't being observed. That however, was a while ago.

Umbran said:

Well, most discussion of black holes addresses them as steady-state objects. But when you start talking about growth of a hole (say, as a possible route to formation of supermassive holes) the issue comes up. The two basic models I have heard of are: 1)vaguely invoke QM tunneling to get the stuff to jump the gap, and 2) assume the in-falling matter accrues in a shell or ring to such density in finite time that it undergoes gravitational collapse itself. At the time, the latter was deemed problematic, as you'd be expecting the equivalent of yet another kind of supernova event that wasn't being observed. That however, was a while ago.

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I see what you're saying, and I may have heard some comments like this before. The thing is, though, I don't think there's a consensus that the stuff needs to form a "horizon" as far as we in the outside universe are concerned. The infalling matter just redshifts and redshifts, and that's it. So I still wouldn't say that the "tunnelling in" description is really agreed upon.

freyar said:

The infalling matter just redshifts and redshifts, and that's it.

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At the time, there were still some very open questions about information loss and black holes - and for that issue, whether the matter has actually gotten inside the event horizon makes a difference. And then you have to think about *how* it gets in there, or if it ever does. And, since this has impact on hawking radiation, and what information it might carry...

Umbran said:

At the time, there were still some very open questions about information loss and black holes - and for that issue, whether the matter has actually gotten inside the event horizon makes a difference. And then you have to think about *how* it gets in there, or if it ever does. And, since this has impact on hawking radiation, and what information it might carry...

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Some scattered thoughts...

There is Hawkins "quantum perturbations" of the event horizon. Is the event horizon a "perfect" ellipsoid, or does it have perturbations, the ghosts of absorbed particles? When something gets very close to the event horizon, how do we handle the uncertainty in the position? How do we handle the slight bump that (I'm thinking) will occur due to the overlapping fields of the body and the black hole? That apparently dissipates exponentially, but perhaps there are many layers of perturbation which are gradually revealed as the black hole evaporates ...

Can we consider that a black hole has an interior? Is that already a philosophical point of view, since we can't do any kinds of measurements of the interior? The notion of something falling into a black hole (crossing the event horizon) is satisfying as a consistent extension of our common world views, but is it actually justified?

Anyways, thx!

TomB

tomBitonti said:

There is Hawkins "quantum perturbations" of the event horizon. Is the event horizon a "perfect" ellipsoid, or does it have perturbations, the ghosts of absorbed particles? When something gets very close to the event horizon, how do we handle the uncertainty in the position?

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If I recall correctly, we don't have to. In order to carry information about *all* the particles the hole has ever absorbed on one finite surface, those perturbations must be much smaller than the original particles. As far as matter as we know it is concerned, the surface is still pretty much flat.

Can we consider that a black hole has an interior?

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Yes. Remember - the event horizon is actually nothing special, in and of itself! There is no discontinuity of space or time there, from the point of view of one approaching it. The space just inside the line is pretty much exactly like the space outside. It is only near the singularity that things to haywire.

Is that already a philosophical point of view, since we can't do any kinds of measurements of the interior?

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You can do measurements of it - it is just that you can only tell other folks inside the hole with you

The notion of something falling into a black hole (crossing the event horizon) is satisfying as a consistent extension of our common world views, but is it actually justified?

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The math tells us it is entirely justified. The space is quite real and pretty much normal. Some are tempted to wave away the math, and say, "Well, since we cannot see it, it isn't really there," but look how well that generally works out...