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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

#51

Post by mrkeen »

imzadi wrote: post #23

Would this apply also to the singularity at the beginning of the universe? I guess I thought that the singularity was where all matter is compressed so much that it occupies a zero dimension point. I'm not sure if that applies equally to black holes and the singularity at the beginning of the universe. I'm kind of dumb on this stuff even though it fascinates me.

The big bang didn't happen at a single point, it happened everywhere. You can look out from anywhere and see the cosmic background radiation having expanded from your location, wherever that location might be.

Re: Black hole singularity is a surface not a point

#52

Post by hackingonempty »

imzadi wrote: post #23

Would this apply also to the singularity at the beginning of the universe? I guess I thought that the singularity was where all matter is compressed so much that it occupies a zero dimension point. I'm not sure if that applies equally to black holes and the singularity at the beginning of the universe. I'm kind of dumb on this stuff even though it fascinates me.

Physicists say a singularity is a classical prediction so most likely wrong.

Re: Black hole singularity is a surface not a point

#53

Post by beeandapenguin »

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…

Kinda sounds like a "linguistic manifold."

Re: Black hole singularity is a surface not a point

#54

Post by mdavidn »

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.

Re: Black hole singularity is a surface not a point

#55

Post by jimberlage »

pdonis wrote: post #48
Kranar wrote: post #39

Earlier quoted context omitted.

Because it's very misleading. Time and space do not switch places past the event horizon. What happens is that the direction/path between an object and the singularity becomes a timelike dimension, and the direction that plays the role of time outside of the event horizon becomes a spacelike dimension. That is not the same as them swapping or that time becomes space and space becomes time not to mention that space ha…

> Really what it means is that past the event horizon you can use the direction in space between you and the singularity as a way to measure time That's not correct. There is a relationship between the radial coordinate r you are at and the time it will take you, by your clock, to reach the singularity (at least assuming you are freely falling), but that relationship can't be described the way you are describing it.…

Am I understanding this right by thinking - if I was walking toward the black hole past the event horizon, and then I turned around, I would still be walking toward the black hole?

Re: Black hole singularity is a surface not a point

#56

Post by kwoff »

pdonis wrote: post #43
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 space and time coordinates switch places as you cross the event horizon If Susskind's book does in fact say that, it's extremely disappointing to me, because, as a number of other GR textbooks will tell you (e.g., Misner, Thorne & Wheeler and Wald, the two great classic GR textbooks), the "switch places" is an artifact of a particular choice of coordinates (Schwarzschild coordinates), and does not represent any…

Susskind's book does also mention that the event-horizon shenanigans are due to coordinates and not a physical thing. Certainly I'd trust what he says rather than me, so sorry if I was misleading.

(If anyone has the book, it is chapter 6 section "Interchange of Space and Time Dimensions at the Horizon" and the following section points out the singularity is a time (and you can't escape it (in a Schwartzschild model at least) just like you can't escape time). I'm sorry if my wording is still incorrect.).

Re: Black hole singularity is a surface not a point

#57

Post by rf15 »

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.

Re: Black hole singularity is a surface not a point

#58

Post by muvlon »

bell-cot wrote: post #25
dekdrop wrote: post #13

How does one descr blackhole to a non-physicist without losing much accuracy? I just it of a very-dense-object.

"A really interesting and cool thing for astronomers to talk about...but you might want to pray that not one of 'em ever comes within a million trillion miles of the Earth."

Astronomical distances are vast, million trillion miles too far, that's over a hundred thousand light years. There are known stellar-mass black holes within just 2000 light years of the Earth. Heck, there might be a primordial black hole in the inner Oort cloud and not only would it not destroy earth, we'd have (are having) trouble detecting it.

Re: Black hole singularity is a surface not a point

#59

Post by fangspire »

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.

[flagged]

Re: Black hole singularity is a surface not a point

#60

Post by HappMacDonald »

jimberlage wrote: post #55
pdonis wrote: post #48

Earlier quoted context omitted.

> Really what it means is that past the event horizon you can use the direction in space between you and the singularity as a way to measure time That's not correct. There is a relationship between the radial coordinate r you are at and the time it will take you, by your clock, to reach the singularity (at least assuming you are freely falling), but that relationship can't be described the way you are describing it.…

Am I understanding this right by thinking - if I was walking toward the black hole past the event horizon, and then I turned around, I would still be walking toward the black hole?

Once you pass the event horizon, every direction leads to the singularity in your future. Directions "away" from the singularity may still visibly show what things looked like outside of the event horizon before you fell in, but that is from your past. Heading in that direction will not get you back there anymore, you will only find the singularity along that path in your future.
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