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Black hole singularity is a surface not a point

arxiv.org

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Re: Black hole singularity is a surface not a point

#171

Post by sigmoid10 »

eru wrote: post #167
sigmoid10 wrote: post #90

Earlier quoted context omitted.

>The fact that both have the same name They don't just have the same name, they are the same thing. A Schwarzschild black hole has both: a removable singularity at the event horizon that is just an artefact of a particular choice of coordinates and a true non-removable mathematical singularity at r=0 where curvature really does go to infinity. It also wouldn't be much of an issue in classical physics, because this si…

Even without quantum mechanics, black holes are trouble: Approximately everything in nature rotates. Including black holes. Schwarzschild blockholes do not rotate. Rotating black holes are much more complicated and don't necessarily shield their singularity behind an event horizon.

Rotating black holes are described by Kerr geometries and have more than one event horizon, but still have their singularities hidden from anyone outside behind their inner horizon.

Re: Black hole singularity is a surface not a point

#172

Post by codesnik »

PaulHoule wrote: post #91
SoftTalker wrote: post #67

Earlier quoted context omitted.

The way Brian Cox puts it, a singularity is a point in time: the end of time. I have trouble really conceptualizing black hole physics, I just think of it as a mass so great that nothing, including light, can escape its gravity. Works for me.

The singularity in a non-rotating, non-charged black hole is as you say. It’s like in a finite amount of time you “run out of time”, like there isn’t any more time on that trajectory. The singularity in a rotating black hole is entirely different but the interior of classical Kerr (rotating) black holes is one of the most controversial if inconsequential topics in theoretical physics because there are reasons to beli…

and some rotation probably inevitable anyway, and non-rotating black holes could be just a mathematical construct, no?

Re: Black hole singularity is a surface not a point

#173

Post by senderista »

zmgsabst wrote: post #138
senderista wrote: post #132

Earlier quoted context omitted.

> 1. I must admit to a lack of sufficient GR education to feel confident in this, but I think that one of the issues that made physicists unwilling to accept the idea of black holes when they were first postulated was that there ended up being a division by zero in the mathematics. Well, the Ricci curvature scalar blows up to infinity, which is obviously unphysical.

Why is it unphysical?

The curvature scalar can be physically evaluated by measuring the volume of a small ball of freely falling test particles and comparing to its volume in flat spacetime.

https://en.wikipedia.org/wiki/Scalar_curvature#Relation_betw...

Re: Black hole singularity is a surface not a point

#174

Post by skirmish »

inigyou wrote: post #163
catlifeonmars wrote: post #153

Earlier quoted context omitted.

This is like saying the Riemann zeta function is only defined for real numbers. You can always extend the singularity mathematically by incorporating new axioms. My point is, it’s not super meaningful to argue whether a black hole has an inside.

I don't mean the coordinate singularity, I mean there is no more spacetime after that.

Why would that happen? In a different coordinate system (Kruskal–Szekeres coordinates) nothing special happens at the event horizon at all.

Re: Black hole singularity is a surface not a point

#175

Post by shrx »

werdnapk wrote: post #140
SoftTalker wrote: post #135

Earlier quoted context omitted.

To be honest I really can't get past what "the end of time" even means.

If it signifies the end of time, then all the stuff in the black hole would need to no longer exist no? If anything is happening in the black hole, then time is still progressing, so nothing must be all that exists?

Time is necessary for change, not existence.

Re: Black hole singularity is a surface not a point

#176

Post by sigmoid10 »

flavenstein wrote: post #133
kadoban wrote: post #122

Earlier quoted context omitted.

> The problems start once you consider quantum mechanics, because any such singularity will break unitarity (a fancy way of saying that probabilities must add up to 1), which means your theory as a whole can no longer make predictions. How is this any different than classical? Isn't it still just an ~impossibility hidden behind an event horizon in either model?

With our current understanding, baryon and lepton number are not conserved as a black hole radiates. I think this is a better demonstration of the incompatibility with classical and quantum mechanics.

Baryon and lepton number conservation are what's called "accidental symmetries" in the standard models, meaning there is no real underlying symmetry that would conserve them. In fact many extensions of the Standard Model don't, while still retaining unitarity. The problems already start once you try to calculate any time evolution of anything, because the Hilbert operator not being unitary means that everything breaks. Even the total energy in a closed system might vanish or blow up to infinity. You can't calculate anything under these conditions.

Re: Black hole singularity is a surface not a point

#177

Post by sigmoid10 »

NooneAtAll3 wrote: post #114
sigmoid10 wrote: post #90

Earlier quoted context omitted.

>The fact that both have the same name They don't just have the same name, they are the same thing. A Schwarzschild black hole has both: a removable singularity at the event horizon that is just an artefact of a particular choice of coordinates and a true non-removable mathematical singularity at r=0 where curvature really does go to infinity. It also wouldn't be much of an issue in classical physics, because this si…

OSM - slight generalization of Schwarzshild BH, where you take evolving spherically-symmetric mass distribution instead of point mass - shows that point singularity in the middle can be naked (aka observable), so it's not just QM that causes worms... https://en.wikipedia.org/wiki/Oppenheimer–Snyder_model

It is not difficult to construct geometries with naked singularities. Reissner, Nordström, Weyl and others individually came up with one long before Oppenheimer. You can also construct geometries where faster than light travel is possible. But all of these suffer from fundamentally unphysical energy conditions. Quantum mechanics may change the picture because it allows weirder energy states than normal physics because everything fluctuates. But it is unknown if and how this actually affects gravity.

Re: Black hole singularity is a surface not a point

#178

Post by automatic6131 »

DrJokepu wrote: post #165

I have a question for any physicists here. Due to my engineering background, I know just enough physics and mathematics to completely misunderstand general relativity and quantum mechanics. However, one pattern I have noticed is that one favorite past time of physicists is looking at the mathematical models, trying to find insane ass edge cases and then trying to interpret them. With that in mind, do these equations…

Yeah. I can't do the physics myself, so I take on faith (heh) that a sufficiently fast rotating blackhole has a ring shaped singularity that can extend outside its' event horizon.

This was news in the 90s and it was a plot point in at least two scifi books, though I don't think I can recommend either

Re: Black hole singularity is a surface not a point

#179

Post by fooker »

DrJokepu wrote: post #165

I have a question for any physicists here. Due to my engineering background, I know just enough physics and mathematics to completely misunderstand general relativity and quantum mechanics. However, one pattern I have noticed is that one favorite past time of physicists is looking at the mathematical models, trying to find insane ass edge cases and then trying to interpret them. With that in mind, do these equations…

The reason is that these edge cases often expose where the current models can break down.

If the current accepted theory is predicting negative mass or infinite mass, it doesn't really mean that a physicist deeply believes we are going to be finding particles with negative mass. It's more likely we'll find a better theory.

In some rare cases, these mathematical oddities do turn out to be real. We found equations producing negative energy as solutions long before we discovered antimatter.

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