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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

#141

Post by the-mitr »

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.

Some of the most interesting and fundamental ideas in science are counter-intuitive

Re: Black hole singularity is a surface not a point

#142

Post by rramon »

somat wrote: post #115
saimiam wrote: post #104

Earlier quoted context omitted.

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)?

My rather limited understanding is that. first there is a lot going on and due to the forces and gravitational gradients involved, matter itself probably would not survive the journey that close to the horizon. But ignoring that, When in compressed time, from the point of view of someone freefalling, timewise everything is normal, the rest of the universe has accelerated and in the case of a black hole has just aged…

I can only guess as well, infinite time compression might result in a big bang when it applies to everything. All black holes could lead to the same moment causing the bang.

Re: Black hole singularity is a surface not a point

#143

Post by snowwrestler »

sigmoid10 wrote: post #61
pdonis wrote: post #43

Earlier quoted context omitted.

> 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…

Kruskal-Szeres coordinates indeed get rid of the wonky coordinate stuff at the event horizon, but if you look at the corresponding diagrams, you'll just end up with the same confusion, because the singularity is still a point (or rather surface) in the future instead of a point in space. The issue is that these diagrams are for eternal, static black holes, which cause diagrams to have these weirdly stretched infinite…

This article is great but the references to gravitational waves as if they were an observed fact (in 1972) was mystifying to me. It led me down a rabbit hole to Joe Weber, who is name-checked at the end of the Penrose article.

A Fleeting Detection of Gravitational Waves

https://physics.aps.org/story/v16/st19

Gravitational wave blues

https://aeon.co/essays/how-joe-weber-s-gravity-ripples-turne...

Re: Black hole singularity is a surface not a point

#144

Post by saimiam »

somat wrote: post #115
saimiam wrote: post #104

Earlier quoted context omitted.

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)?

My rather limited understanding is that. first there is a lot going on and due to the forces and gravitational gradients involved, matter itself probably would not survive the journey that close to the horizon. But ignoring that, When in compressed time, from the point of view of someone freefalling, timewise everything is normal, the rest of the universe has accelerated and in the case of a black hole has just aged…

> external point of view

So time is localised? I’m not sure what localised time means but I’m hoping the question makes sense.

Re: Black hole singularity is a surface not a point

#145

Post by bmitc »

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 taken a graduate level class in General Relativity would have been able to tell you the same.

You say that and yet this thread is full of people arguing about it, and there's an entire Wikipedia article on this: https://en.wikipedia.org/wiki/Gravitational_singularity.

In fact, that article says:

> No complete and precise definition of singularities exist in the theory of general relativity,

So which is it? It can't both be trivial to any grad student but also an open question. And things like naked singularities aren't proven to not exist either.

Also, general relativity is a classical, geometric-only theory. It seems obvious that better understanding what a black hole's singularity is would require quantum mechanics because the singularity is effectively what's "left over" of the physical material once you go beyond a neutron star.

Re: Black hole singularity is a surface not a point

#146

Post by ambicapter »

gerdesj wrote: post #125
ghosty141 wrote: post #111

Earlier quoted context omitted.

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.

Using a compass is interesting, use two razor blades taped together is much easier and it’s close enough to perfect parallel lines.

Re: Black hole singularity is a surface not a point

#147

Post by teamonkey »

XorNot wrote: post #84
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 more interesting component is that black hole physics is almost an anti-free will zone. Everywhere else in the universe with mass and energy you can do what you want (sort of). An event horizon throws a hard shroud over that and drastically reduces opportunities: your free will to use mass and energy is significantly curtailed (you must head towards the singularity).

I’m not sure free will has anything to do with it.

If you don’t have enough upward velocity to escape earths gravity, hitting the ground is also inevitable.

Re: Black hole singularity is a surface not a point

#148

Post by dredmorbius »

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)?

Time acceleration is dependent on the gravitational flux.

All objects within a given radius of the black hole (possibly modulo spin) would experience the same time dilation. Remote objects in the universe would not experience the dilation.

From the perspective of the astronaut falling toward the singularity, the rest of the Universe would age at an ever-increasing rate.

From the perspective of a remote observer, the astronaut falling toward the singularity would be experiencing time at an ever-decreasing rate.

The notion of relativity is that time-perception is relative, and dependent on acceleration, whether from motion (as on a spaceship) or from gravitational acceleration (as near a black hole). Objects in orbit around Earth, further from Earth's centre, and hence subject to reduced gravitational acceleration, age more quickly than objects on Earth's surface. This is actually measurable using atomic clocks, though the effect is quite small. It is sufficient that GPS satellites require time correction.

Re: Black hole singularity is a surface not a point

#149

Post by inigyou »

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…

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

Re: Black hole singularity is a surface not a point

#150

Post by inigyou »

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…

But then you "fill up all the photon slots" too (not literally because they are not fermions, but they do spontaneously convert back into things like electrons at that density) and you can work around the Pauli exclusion principle by stacking your electrons at higher and higher energy levels.

Pauli exclusion isn't an impenetrable force field - as you say, it's just often more favourable to do something else than to work around it. Consider an iron atom with however many electrons though - all those orbitals except the inner one are electrons working around Pauli.

I'm not a physicist either.

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