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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

#131

Post by Dylan16807 »

725686 wrote: post #112
mrkeen wrote: post #51

Earlier quoted context omitted.

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.

Doesn't that imply that, "everywhere" was, precisely, a single point?

No, why would it imply that?

One theory that might help you visualize an alternative is that the big bang was basically two 3D universes (floating in higher-dimensional space) slapping against each other really hard. That creates an explosion everywhere even if everywhere is quite big or even infinite.

Re: Black hole singularity is a surface not a point

#132

Post by senderista »

dhosek wrote: post #81
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.

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…

> 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.

Re: Black hole singularity is a surface not a point

#133

Post by flavenstein »

kadoban wrote: post #122
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…

> 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.

Re: Black hole singularity is a surface not a point

#134

Post by Dylan16807 »

bell-cot wrote: post #74
misnome wrote: post #49

Earlier quoted context omitted.

Unfortunately, there is a rather large one not one sixth of that distance away (a million trillion miles is actually rather large - 170 kly - approximately double the size of our galaxy)

Yes - I took the grandparent comment's "descr to a non-physicist" as "describe to someone who really isn't into math or hard sciences". Those folks will hear "million trillion" as "a really Really REALLY REALLY big number". Not as "1 x 10^18".

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 problems. And we really have no idea what the smallest existing black hole is.

Re: Black hole singularity is a surface not a point

#135

Post by SoftTalker »

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…

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

Re: Black hole singularity is a surface not a point

#136

Post by aeve890 »

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…

>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

Well, isn't called space-time for nothing. You can't have one without the other. Like in electromagnetism. I thought it was kinda obvious since Einstein and Minkowsky.

Re: Black hole singularity is a surface not a point

#137

Post by [deleted] »

drdeca wrote: post #109
kevindamm wrote: post #72

Earlier quoted context omitted.

Kind of, but not really.. though there are simple models with electrons as a point charge, a more accurate model involves the electron field describing the probability of an electron existing at any region in space (not to be confused with the electromagnetic field, the medium in which photons propagate).

Sure the position of an electron is not definite, but neither is that of a buckyball, but a buckyball has a shape we can describe, an internal structure we regard as extended over space, in a way that is separate from the indeterminacy of its center of mass position. This is unlike an electron, for which, if we set aside the uncertainty as to its center of mass, my understanding is that the only internal degrees of f…

[deleted]

Re: Black hole singularity is a surface not a point

#138

Post by zmgsabst »

senderista wrote: post #132
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…

> 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?

Re: Black hole singularity is a surface not a point

#140

Post by werdnapk »

SoftTalker wrote: post #135
PaulHoule wrote: post #91

Earlier quoted context omitted.

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…

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?
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