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Black hole singularity is a surface not a point

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Re: Black hole singularity is a surface not a point

#121

Post by pfdietz »

ck2 wrote: post #44
1970-01-01 wrote: post #28

Earlier quoted context omitted.

Yes, magnetars are considerably more rare than black holes and considerably more interesting to study in terms of raw horsepower. Imagine a type-2 civilization using them as engines or launchers for spacecraft to zip around the galaxy.

the radiation from a magnetar exceeds any other star, overcoming that would seem implausible still trying to wrap my mind around kilonovas (colliding neutron stars) ie. they can pop out earth-sized chunks of gold, in theory, and since they aren't black holes that would be VISIBLE, albeit also "in theory" lol * https://www.nasa.gov/image-article/unfolding-story-of-kilono... maybe Roman can spot one someday, that would…

> they can pop out earth-sized chunks of gold

The can produce Earth masses of gold, but of course not in the form of "chunks". The gold starts as atoms in a highly ionized gas and only much later cools enough to form solids (dust).

Re: Black hole singularity is a surface not a point

#122

Post by kadoban »

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…

> 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?

Re: Black hole singularity is a surface not a point

#123

Post by sfink »

PaulHoule wrote: post #95
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/Russi…

Well, the analogy is to something flying by a black hole and having its trajectory altered.[1] It sounds like it fits you, then -- you interacted, and are now forever irritated by them or by things that sound like them, even things that you would not have previously noticed.

[1] This is just gravity, nothing specific to black holes, so the analogy isn't doing a lot of work here.

Re: Black hole singularity is a surface not a point

#124

Post by goatlover »

TheOtherHobbes wrote: post #107
goatlover wrote: post #68

Earlier quoted context omitted.

Aren't fundamental particles like electrons and quarks treated as points?

Points are a realist view - there's a real object there. Although some physicists disagree, QM slants very anti-realist. There are no objects anywhere, no particles, no waves, only probabilistic interactions, some of which can be snapshotted into localised partially definite results. So there are only interactions between probability distributions in space and time, and "particle-like events." No pointy objects, and…

QM slanting anit-realist is because some prominent physicists like Neils Bohr gave the math that interpretation, and they were more persuasive than the realists like Einstein, Schrodinger, Everett.

The agnostic view is it's just a mathematical model that makes accurate probabilistic predictions when measurements are made, which says nothing about what's really going on.

Of course treating particles as points is also mathematical.

Re: Black hole singularity is a surface not a point

#125

Post by gerdesj »

ghosty141 wrote: post #111
cvoss wrote: post #77

Earlier quoted context omitted.

Common sense cannot be trusted on matters like these. Common sense is calibrated for reasoning over matters encountered in daily life. The further away we get from that, into more and more exotic phenomena, the less common sense can apply. Black holes are very far from the domain of common sense.

I always suggest looking at the quantum eraser experiment to see how bad common sense works with quantum mechanics. It's fairly simple but intuition fails most people when it comes to explaining how it works.

No need for funky stuff, just do the classic (lol) Young's slits experiment which should be more than enough oddness for anyone.

I was shown it at school, using microscope glass slides that we waved over a Bunsen burner running cold, to coat with soot. We then carefully etched parallel lines with a compass by hand. Our (~17 y/o) efforts were a bit random but we did get some smudgy banding results on the screen.

Re: Black hole singularity is a surface not a point

#126

Post by pdonis »

sigmoid10 wrote: post #99
pdonis wrote: post #86

Earlier quoted context omitted.

> 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 bla…

> It also is in Schwarzschild coords

True--indeed, the statement that it's a spacelike line is an invariant, independent of any choice of coordinates. But it's a lot harder to see that in Schwarzschild 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.

I disagree, and I think many GR physicists would as well. Indeed, both classic GR textbooks, Misner, Thorne & Wheeler (1973) and Wald (1984) discuss Kruskal coordinates and their associated spacetime diagram (MTW in Box 31.2 and sections 31.5 and 31.5, Wald in section 6.4), and those discussions contain a good deal more than just showing that the horizon is "not such a weird place".

Re: Black hole singularity is a surface not a point

#127

Post by cscheid »

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

Re: Black hole singularity is a surface not a point

#128

Post by pdonis »

sigmoid10 wrote: post #105
XorNot wrote: post #82

Earlier quoted context omitted.

This doesn't seem meaningfully different to me? Like the notion that the singularity is always in your future (because you can't escape it anymore past the event horizon) makes sense, the point of confusion is what are the implications? Roughly the general public (including me) knows that gravity is meant to have some effect on the apparent passage of time, so it seems significant but under explained what it means to…

>the notion that the singularity is always in your future makes sense But it is just a mathematical artefact of weirdly chosen coordinates. In reality, the singularity is still just a point in space (or a line in spacetime), except that inside the event horizon all paths you are allowed to travel lead to it. There's no need for this whole "space turns into time" notion apart from the fact that you are guaranteed to h…

> 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 time, not a place in space.

> There's no need for this whole "space turns into time" notion

That's true; that notion is an artifact of Schwarzschild coordinates. But that does not imply the other claims you are making.

> the spatial coordinates of the singularity

I'm not sure what you mean by this. It's true that, since the singularity is a spacelike line, you can treat a coordinate that varies along it as a "spatial" coordinate marking different spatial points on the singularity. But the singularity itself is a moment of time (as above, a spacelike line), so it is not a "place", and it does not have a particular set of "spatial coordinates". A spatial coordinate marking different points along the singularity is marking different points in space at a moment of time.

Re: Black hole singularity is a surface not a point

#129

Post by rcxdude »

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!

I mean, it's kind of both: objects have gravity, which attract them together, which creates more gravity and larger objects. Stars are what happens when the rest of physics disagrees with this (and black holes are when gravity wins anyway).

Re: Black hole singularity is a surface not a point

#130

Post by sfink »

mrkeen wrote: post #51
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.

> The big bang didn't happen at a single point, it happened everywhere.

A bit of an odd thing to say, since "everywhere" implies there are multiple places to be, and at the instant of the big bang, there was only place to be. So it was both everywhere and at a single point: it was at all of the single place there was to be.

But your point (sorry) about expansion being from everywhere isn't specific to the big bang; space was expanding well after the big bang and it doesn't seem like the expansion ever had a "center" (at least, not since not-center places existed). It's expanding from everywhere. (But evenly everywhere? I have no idea. Hey, maybe black holes are like buttons in cloth, and it expanded everywhere except for where the buttons were holding things still at a rate relative to distance from the button. A brilliant hypothesis that explains exactly zero unexplained phenomena, at least none that I know of.)

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