Black hole singularity is a surface not a point • Hacker News Board

Re: Black hole singularity is a surface not a point

#161

Post by inigyou » Wed, Aug 26, 2026, 3:46 AM UTC

mdavidn wrote: post #54

ck2 wrote: post #6

what's really going to blow your mind is while you probably assumed or knew spinning black holes move space around them spinning black holes also move TIME around them * https://www.science.org/doi/10.1126/sciadv.ady9068 so in theory a spinning black hole that's been around for billions of years has a time drag around it in a path that is billions of years old (no we can't navigate it because yes that would be time t…

It blows my mind that, in the frame of an outside observer, time appears to stop at the event horizon. An observer falling through the horizon (who survived the radiation and tidal forces) would not perceive this.

Assuming they do fall through it. Remember they're about to receive an entire universe lifetime's stellar radiation compressed into a microsecond.

(Which is another reason some people think we might be living inside a black hole. An entire universe of energy released in zero time is literally a Big Bang. It would form into stars and galaxies.)

Re: Black hole singularity is a surface not a point

#162

Post by jibal » Wed, Aug 26, 2026, 3:48 AM UTC

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.

It's a complete violation of good sense to invoke common sense here. You talk about "particles" but that's not what the world is made of. Also, particle/wave duality. Also, any number of bosons can occupy the same position. Also black holes evaporate. And on and on.

Re: Black hole singularity is a surface not a point

#163

Post by inigyou » Wed, Aug 26, 2026, 3:54 AM UTC

catlifeonmars wrote: post #153

inigyou wrote: post #149

Earlier quoted context omitted.

We don't actually know if a black hole has an inside. Some theories/hypotheses say spacetime just stops at the event horizon.

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.

Re: Black hole singularity is a surface not a point

#164

Post by AgentME » Wed, Aug 26, 2026, 4:05 AM UTC

saimiam wrote: post #104

somat wrote: post #98

Earlier quoted context omitted.

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...…

Does time accelerate just for the astronaut approaching the black hole (meaning they would be witnessing the future) or does it accelerate for everyone (meaning approaching a black hole is going to make everything end quicker)?

If outside observers could watch the astronaut clearly, the astronaut would look like they're slowing down to a stop at the event horizon. The astronaut would not see themselves freezing in time, but they would see everything outside of the black hole speed up.

You could travel arbitrarily far into the future by getting close to a black hole's event horizon for a while without crossing it and then leaving, assuming you had the energy for it and you didn't get obliterated by all the mass and energy falling into the black hole in that timeframe.

Re: Black hole singularity is a surface not a point

#165

Post by DrJokepu » Wed, Aug 26, 2026, 5:09 AM UTC

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 allow black holes whose singularities extend beyond their event horizons?

Re: Black hole singularity is a surface not a point

#166

Post by georgeburdell » Wed, Aug 26, 2026, 5:14 AM UTC

tux3 wrote: post #120

shagie wrote: post #73

Earlier quoted context omitted.

The question of "what holds it up?" is where that leads to. There's an interesting history of answering that question again and again - and the discovery of new types of stars each time. History of the Universe : What Is Hidden In The Core Of A Neutron Star? - https://youtu.be/YoYjkNQ27T8 That video goes into it... without getting mathy at any point. One of the bits that you're having trouble with is the compression…

>Rather than compressing particles [...] If you packed enough photons into one spot I haven't watched the video, but if we're compressing electrons, neutrons, or other fermions, I imagine if we want to keep compressing that down to an arbitrarily small radius, won't we pretty quickly find it favorable to shift those fermions to something else , probably photons, to respect Pauli exclusion? Really, I don't know enough…

Pauli Exclusion is just another “force” that can be overridden. Nature isn’t a list of rules

Re: Black hole singularity is a surface not a point

#167

Post by eru » Wed, Aug 26, 2026, 5:17 AM UTC

sigmoid10 wrote: post #90

dhosek wrote: post #81

Earlier quoted context omitted.

I figure at least some of it comes from the idea that mathematically, a singularity is a point (e.g., in the graph of z=1/w, there is a singularity at the point w=0, and in the graph of z=(1-w)²/(1-w) there is a removable singularity at w=1 (that is, the function is undefined at w=1, but if you put a point at (1,0), the graph will be continuous and no longer have any holes in it). The fact that both have the same nam…

>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.

Re: Black hole singularity is a surface not a point

#168

Post by eru » Wed, Aug 26, 2026, 5:19 AM UTC

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.

As far as anyone knows, electrons are already point masses.

Re: Black hole singularity is a surface not a point

#169

Post by eru » Wed, Aug 26, 2026, 5:20 AM UTC

cscheid wrote: post #127

tux3 wrote: post #120

Earlier quoted context omitted.

>Rather than compressing particles [...] If you packed enough photons into one spot I haven't watched the video, but if we're compressing electrons, neutrons, or other fermions, I imagine if we want to keep compressing that down to an arbitrarily small radius, won't we pretty quickly find it favorable to shift those fermions to something else , probably photons, to respect Pauli exclusion? Really, I don't know enough…

Pauli exclusion is a QM thing. Black holes are a GR thing. Famously, we don’t know how to mix the two.

We don't know how to mix the two in general. There are plenty of tame enough special cases where we know how a mixture has to look like.

Finding a tame enough special case was how Hawking discovered his radiation.

Re: Black hole singularity is a surface not a point

#170

Post by eru » Wed, Aug 26, 2026, 5:22 AM UTC

XorNot wrote: post #78

rf15 wrote: post #57

Earlier quoted context omitted.

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.

Common sense - the experience gained from your common everyday experience of reality - does not apply in black holes. Common sense would tell you they can't exist at all because you can't compress atoms - you have lived your entire life with atoms being entirely incompressible for the practical purpose of anything you do. Leaning on common sense to discuss fundamental physics has been wrong since round about the star…

Funnily enough, technical speaking atoms are a small minority of ordinary matter, that is already excluding dark matter.

That's because a lot of the ordinary mass in the universe is ionised or in other weirder states.