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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

#211

Post by pdonis »

sigmoid10 wrote: post #194
pdonis wrote: post #128

Earlier quoted context omitted.

> it is just a mathematical artefact of weirdly chosen coordinates. No, that's not correct. The fact that the singularity is always in your future inside the horizon is an invariant, independent of any choice of coordinates. > the singularity is still just a point in space No, it's not. A point in space would be a timelike line in spacetime. But the singularity is a spacelike line in spacetime. That's a moment of tim…

Just draw the geometry in Eddington Finkelstein coordinates and you will see everything I wrote above is true at the technical level if you read precisely.

No, everything you wrote is not true, in Eddington Finkelstein or any other coordinates. You wrote that the singularity is a point in space. It's not, no matter what coordinates you choose. It's a line in spacetime, but it's a spacelike line, and a spacelike line cannot describe a point in space. It can only describe a moment of time. No choice of coordinates can change that. (Similar remarks apply to your claim that the singularity always being in your future once you're inside the horizon is an artifact of a coordinate choice. It's not. It's just as true in Eddington-Finkelstein coordinates, or any others.)

That also makes your use of the term "spatial coordinates" questionable, as I already pointed out. The fact that the line r = 0 is vertical in an Eddington-Finkelstein spacetime diagram does not mean it's automatically a "point in space" or that r inside the horizon is automatically a "spatial coordinate". You need to look at the actual physics, not just the surface appearance of the diagram.

Re: Black hole singularity is a surface not a point

#212

Post by vee-kay »

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.

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Re: Black hole singularity is a surface not a point

#213

Post by WhitneyLand »

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.

That’s only true regarding the one sentence about the singularity not being a point.

People like to reduce papers to a simple hot take, but the paper is more than that, offers viewpoints that are non-standard and speculation about new possibilities.

Re: Black hole singularity is a surface not a point

#214

Post by BjoernKW »

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.

Anyone who has watched Interstellar should know this.

Re: Black hole singularity is a surface not a point

#215

Post by kakacik »

inigyou wrote: post #161
mdavidn wrote: post #54

Earlier quoted context omitted.

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.)

You would turn into plasma cloud long before getting there. How your specific atoms or parts of them, highly separated across long distances perceive that moment is practically irrelevant

Re: Black hole singularity is a surface not a point

#217

Post by My_Name »

marcyb5st wrote: post #181
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…

Time travel breaks causality if you assume Copenhagen interpretation of quantum mechanics. Multi-world interpretation allows it as you just end up in a self-consistent "branch" and you would be stuck there. Like you can travel back in time and kill one of your ancestors before he/she had children. In that branch you wouldn't be born, but since you come from another branch the system remain consistent. (If you are int…

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Re: Black hole singularity is a surface not a point

#218

Post by Obscurity4340 »

raattgift wrote: post #198
amelius wrote: post #180

> Counterintuitively, in general relativity two points can be spatially close yet causally distant. Can the converse also be true in general relativity?

Yes, during cosmic inflation for example: two test objects initially close can end up many light-years apart. If we make these test objects null (i.e., lightlike) then we can always contrive an inflation that stretches them apart in such a way that they still meet again. Some exotic spacetimes involving pp-wave sandwiches can focus initially non-converging and spatially distant light pencils onto each other at a caus…

Where or encroaching upon what does the univerise expand into? If the universe is all the real estate of physical reality, what is it subsuming as it expands in order to accomodate that growth?

Re: Black hole singularity is a surface not a point

#219

Post by inigyou »

catlifeonmars wrote: post #209
inigyou wrote: post #208

Earlier quoted context omitted.

Why wouldn't it happen? From the perspective of anyone outside the black hole, nothing can ever enter it. What if that's just true ?

Have you considered that the apparent event horizon is not uniform for all observers? So does spacetime exist in some frames of reference but not others because those frames disagree on the radius of the apparent event horizon? Also note that in general an event horizon doesn’t require a singularity.

All observers outside the black hole agree that nothing ever enters the black hole though.

Re: Black hole singularity is a surface not a point

#220

Post by Dylan16807 »

sfn42 wrote: post #195
Dylan16807 wrote: post #134

Earlier quoted context omitted.

I guess, but "light year" is easy to say, easy to understand, and much less likely to mislead. And most black holes would probably be safe at that distance. Though the issue of small black holes is worth bringing up. If you scrunch up one cubic kilometer of stone into a black hole, that's heavy to be stable for trillions of years, but light enough to pass between the Earth and the moon without causing serious problem…

You'd be surprised how may people don't even understand that a light year is a measure of distance.

Hmm. Well even then I think a million million miles will suffice, that's over ten thousand AU, .17 light years.
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