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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

#91

Post by PaulHoule »

SoftTalker wrote: post #67
kwoff wrote: post #12

Earlier quoted context omitted.

Or read Susskind's "The Theoretical Minimum: General Relativity". For a non-spinning blackhole at least, not only is the singularity not a point, it is a surface in time, not space (as the book explains, the space and time coordinates switch places as you cross the event horizon).

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 believe (without real proof mind you) the Kerr solution is unstable inside the inner event horizon so that whatever happens in there is not what that theory says.

And of course black holes are quantum objects which might actually have an “interior” entirely different from the classical picture.

Re: Black hole singularity is a surface not a point

#92

Post by metalman »

treating a black hole as a point, or ;) pointicle,may be valid as matter may be condensed, to the, I mean ,in such a way that there is NO space left whatsoever, and therefor no room for physical dimensions to exist in, and the entire body functions as an undiferentiated body of stuff, or giant pointicle that destroys time and space. Hopefully very soon we will get news about our galaxys central black holes interaction with a star that is orbiting very close but at 8% light speed, which may reveal if our blackhole is spinning, and if that is the case the we would have proof of energy/information/gravity waves? escaping from a black hole, along with gravity which while apparently imune to its self, nothing else is so far.

Re: Black hole singularity is a surface not a point

#93

Post by kazinator »

> Black hole singularity is a surface not a point

Might they be trying to say this?

1. The boundary of the black hole which traps light, etc, is called the event horizon, and sits at the Schwarzschild radius. This is a geometric surface.

2. There is no singularity at this surface.

3. In models of black holes, there is a gravitational singularity at a point in the centre: https://en.wikipedia.org/wiki/Gravitational_singularity which is a topic with nuances.

Re: Black hole singularity is a surface not a point

#95

Post by PaulHoule »

sfink wrote: post #46

Off-topic, but it makes me think of "reasoning black holes": you get enough like-minded people together that they start reinforcing each other's logic and beliefs until not only those people get completely detached from reality, but anyone who interacts with them gets sucked in as well unless their own logic ("velocity") is adequate to skirt the edge and escape, forever altered by the experience. Similar questions ar…

I dunno. Those rationalists seem to be in some kind of intellectual black hole which never had any danger of sucking me in. Like I have seen many strands of posthumanism and transhumanism, speculations about an intelligence explosion circa 1970, and figure it would have been just as much fun to sit around the campfire, pass a joint around, and talk about crazy stuff with these guys

https://en.wikipedia.org/wiki/Russian_cosmism

as it would be to do with anyone contemporary. In their orbit I get periodically annoyed but changed forever, no.

Re: Black hole singularity is a surface not a point

#96

Post by lopsotronic »

0x20cowboy wrote: post #33
ben_w wrote: post #24

Earlier quoted context omitted.

Normally people think of gravity as pulling on objects. You can instead think of it as pulling on the space those objects are in. A black hole happens when there is enough gravity that space gets pulled inwards somewhere, at at least the speed of light. Gravity falls off with distance, and the distance where space is being pulled inwards at exactly the speed of light is called the "event horizon". It has this name be…

> Normally people think of gravity as pulling on objects. You can instead think of it as pulling on the space those objects are in. (Very uneducated person here) I’ve always wondered if large objects caused gravity, or if maybe large objects form in the places where there is a lot of gravity. This is probably elementary, but I’ve never looked in to it. Maybe today is the day!

If you want to take a very large-scale - if poetic - view of things, you could also (very arguably) say something like "Mass is Fate".

Mass represents a zone where probabilities want to be. The more that aggregate, the more they make other things want to glom on. With a high enough density, nothing that's nearby can glom to literally anywhere else, and there's your black hole. The Great Inevitable. In this space, there are no other possibilities. Very Demiurge-y.

Re: Black hole singularity is a surface not a point

#98

Post by somat »

rf15 wrote: post #57
sigmoid10 wrote: post #2

Should be pointed out that this is a critique of common popsci journalism tropes and not a fancy new research result. Anyone who has taken a graduate level class in General Relativity would have been able to tell you the same.

As someone with basically only popsci knowledge of black holes: people claiming it would be a literal point never made much sense - fundamentally, common sense (as much as it can apply here) dictates that you cannot compress particles to an absolute point.

My rather pop-sci understanding is that when you start playing around with relativity math, trying various masses and densities you hit something rather worrisome. As you approach some great, but still possible, value the plot goes infinite, the singularity. This is bad for the theory because going asymptotic like that usually indicates a fundamental problem in the math. But relativity does so well everywhere else... What if it could? And thus the black hole was born.

The easy thing to miss, and blew my mind when I read it. is that general relativity is the concept of space-time, emphasis on the time, and this is also compressed by the mass, so if this singularity can actually occur it would also take an infinite amount of time to fall into it. So nothing can actually enter it. From the point of view of an astronaut(deliberately ignoring all the other relativistic implications) flying directly toward the event horizon. As you approach you will quickly see the rest of the universe age and die. and if hawking radiation is real the black hole will evaporate in front of you before you can reach it.

Re: Black hole singularity is a surface not a point

#99

Post by sigmoid10 »

pdonis wrote: post #86
sigmoid10 wrote: post #61

Earlier quoted context omitted.

Kruskal-Szeres coordinates indeed get rid of the wonky coordinate stuff at the event horizon, but if you look at the corresponding diagrams, you'll just end up with the same confusion, because the singularity is still a point (or rather surface) in the future instead of a point in space. The issue is that these diagrams are for eternal, static black holes, which cause diagrams to have these weirdly stretched infinite…

> the singularity is still a point (or rather surface) in the future instead of a point in space. It's a spacelike line on the Kruskal diagram, yes. > The issue is that these diagrams are for eternal, static black holes The full Kruskal diagram is, yes. But the essential features of the black hole portion of that diagram are still there in a black hole that forms by gravitational collapse of a massive body. That incl…

>It's a spacelike line on the Kruskal diagram

It also is in Schwarzschild coords, so you've gained nothing with respect to the original issue from switching coordinates. Kruskal-Szeres really is only useful for demonstrating that the event horizon is not such a weird place, but it does nothing for the singularity at the center.

>the essential features of the black hole portion of that diagram are still there in a black hole that forms by gravitational collapse

The issue is even the limited diagram doesn't really show you that and the full one goes crazy with white holes. So not a good place if you don't want to confuse laypeople.

Re: Black hole singularity is a surface not a point

#100

Post by __MatrixMan__ »

rf15 wrote: post #57
sigmoid10 wrote: post #2

Should be pointed out that this is a critique of common popsci journalism tropes and not a fancy new research result. Anyone who has taken a graduate level class in General Relativity would have been able to tell you the same.

As someone with basically only popsci knowledge of black holes: people claiming it would be a literal point never made much sense - fundamentally, common sense (as much as it can apply here) dictates that you cannot compress particles to an absolute point.

A particle is a region of space where it's probable that a certain kind of interaction will happen. I don't see any reason why they can't overlap infinitely and then squeeze to the Dirac delta function: certain to be here, no error bars. That is, apart from the Pauli exclusion principle. But you have to leave that one behind if you're dealing with masses beyond the TOV limit.

Of course I'm missing something here. I've taken QM and not GR so I would have this interpretation.

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