Talk:Gravitational singularity

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Contents 1 Source 2 Naked Singularities 3 Difference 4 Gravitational singularities and entanglement? 5 This article Desperately needs complete overhaul 6 Singularity existence 7 Intro 8 Singularity exists or singularity existed? 9 I did an overhaul 10 Jumble 11 Belief 12 A question for the cosmologists

[edit] Source

Gravity, by Thorne, Misner, and Wheeler

[edit] Naked Singularities

I read this article and it is rather good although it may aquire some cleaning up. However, I did not see any mention of Naked Singularities. Would that be in a different article, is there anything about naked singularities on Wikipedia, or should I add a section on naked singularities to this article? Cheers!--The Relentless Rogue 02:32, 7 December 2006 (UTC)

[edit] Difference

The article doesn't explain what distinguishes a gravitational singularity from a mathematical singularity in GR equations. I put "sometimes" but someone took it away.

Here's the diff: mathematical singularities don't *always* means gravitational singularities because they can be artifacts of the coordinate system used.

I think, that there is practically, no difference between mathematical and geometrical singularity(ies). In fact, the latter is a practical phenonmenon of theoretical former.. --Krishnavedala 05:40, May 22, 2005 (UTC)

It seems that someone has been messing with the source, and data was lost. As for me the word "Hello" is rathewr unrelated to gravitational singularity ;). Please fix it...

Regards, Adam Hepner (not yet registered wikipedian)

The Gravity book, referenced at the top of this discussion, explains the differences between coordinate singularities, such as the North and South Poles, and real singularities, at length.

[edit] Gravitational singularities and entanglement?

Is it posssible that a pair of gravitational singularities can be entangled in a similarly to how electrons can be entangled?

If they cannot be entangled then can you explain why this concept doesnt work as I am curious to develop this idea?

Delving on the occult there dude ... . ---Mpatel (talk) 14:05, August 21, 2005 (UTC)

1. There are no gravitational singularities.

2. Black holes are not particles. They have the mass of several suns in the space of a proton at most.

[edit] This article Desperately needs complete overhaul

Need to clearly distinguish between geometric and coordinate singularities.

Among latter (aka gravitational singularities, although terminology nonstandard), need to point out that in exact colliding wave solutions, typically you have fold singularities which are geometric (not coordinate artefacts) but are not curvature singularities either.

I think should merge out some material into a new article on Curvature singularity, which should introduce some standard classifications:

• scalar versus nonscalar
• strong versus weak
• spacelike versus timelike versus null (doesn't apply to all curvature singularities)

Both article should link to appropriate examples illustrating these in the Category:Exact solutions in general relativity, which I need to populate myself.---00:04, 15 September 2005 (UTC)

From the first sentence too. You don't need matter, first of all -- vacuum solutions in GR have curvature singularities (eg the Kasner universe). Secondly, beyond the fact that volume is not a relativistically invariant quantity, it doesn't need to go to zero in a singularity, for example in a Big rip. Finally the curvature need not diverge either, as pointed out for the folds in wave collisions.

That said, I'm not sure what a better alternative would be. Maybe something along the lines of A gravitational singularity is a feature of a spacetime, so that the histories of obeserves that encounter it appear to end.? Sounds bad even to me. Any other suggestions? Wesino 15:43, 25 November 2006 (UTC)

[edit] Singularity existence

The article says "singularities can exist even if the curvature of space-time is finite everywhere.". Surely singularities do not exist by definition, since they have have no dimensions? ----

Singularities exists because they have a verifiable, predictable effect on the stuff that is included in reality. The effects of singularites have been observed many times. They may even have dimensions that are definable in another dimension than the three space and one time we are more familiar with in everyday observations..

You two are talking about completely different things. Coordinate singularities like the North Pole and the South Pole exist at points of finite curvature. The other kind, the point mass with infinite density in a region of infinite curvature, simply does not exist, and has not been observed. Nor have any such effects been observed. If we had observational evidence of singularities, physics would be completely different from what it is today.--Cherlin 10:17, 19 October 2006 (UTC)

[edit] Intro

So, is this article about 'gravitational singularity' or 'spatial singularity' (as the intro puts it)? Ben Finn 11:54, 25 August 2006 (UTC)

People get confused (look around this discussion page), so we have to make the distinction.--Cherlin 10:17, 19 October 2006 (UTC)

[edit] Singularity exists or singularity existed?

If we have established that the singularity exists, have we established if it still exists or that it just existed? Any ideas on the arguements or counterarguements for this topic or where the arguements are at right now? (Simonapro 14:59, 29 August 2006 (UTC))

We haven't, because it doesn't. Suppose you could put three solar masses at a mathematical point. Then the uncertainty principle says that its momentum is infinite. At this point the whole thing explodes. Now you might think that this is impossible, because neither particles nor photons can escape from a black hole. But that assumes the constant gravitational field of an unmoving black hole. What we are talking about here is all of the particles escaping at the same time in a spherical shell, leaving nothing at the center. The gravitational force inside the shell is zero everywhere, by a theorem of Isaac Newton.--Cherlin 10:17, 19 October 2006 (UTC)

[edit] I did an overhaul

The answer to most of the questions above is "No". Black holes don't get entangled; they merge. There is no evidence of actual singularities in the cores of black holes or at the time of the Big Bang. The mathematical complications requested above shed no light on the physics, and I won't do them. I'll probably add some references, including one for a detailed discussion of coordinate singularities, when I get home and can get them off the shelf. [Sorry, I didn't] I look forward to the Exact Solutions page. If somebody wants to add stuff on the quantum foam catastrophe in early quantum gravity theories, I'll applaud. Cherlin 2006 August 30

Are you saying that the Big Bang is flawed? If so, how do you explain (1)The age of the Universe according to WMAP and (2)The second law of thermodynamics with regards to a static infinite universe. If you are saying the Big Bang is not flawed, what was before the bang? (Simonapro 19:42, 3 September 2006 (UTC))

Excellent questions. The Big Bang theory is apparently accurate after the presumed first 10 ^{− 44} sec or so. I am saying that we know nothing about the earlier interval from our current understanding of physics. I don't believe that there was a singularity before that. There are several theories of how a small region of spacetime could inflate into a universe. One of them is called "false vacuum". In some versions, the false vacuum region would create new inflationary bubbles with great frequency. This is one of several theories predicting that there are a multitude of what we currently think of as "universes". Probably there should be a page on several of these issues.--Cherlin 10:17, 19 October 2006 (UTC)

[edit] Jumble

Hi there. Seems like this article's in a bit of a mess. First of all, although entitled gravitational singularity, it starts by describing singularities in physics in general (quite well too), before finally getting onto its title subject. The formatting then breaks down such that sections and subsections aren't properly identified and separated. Finally, it ramblingly concludes with poorly formatted "notes" and a reading recommendation. My suggestion would be to create a new article, Singularity (physics), for the material at the head of the current article, then to tidy up the remainder so that its formatting is consistent with Wikipedia standards. For an article that appears in a template bar on GR, it's really quite ugly at the moment. Cheers, --Plumbago 16:09, 29 September 2006 (UTC)

I put in the singularities in physics in general because I don't think you can make sense of this problem without a more general understanding of the ways physics has dealt with mathematical singularities in the past. We could certainly rearrange things.--Cherlin 10:17, 19 October 2006 (UTC)

I have to weigh in on Plumbago's side. I like the discussion of various crises in physics, but I think they belong in their own article. It's not made clear what features they share with gravitational singularities, and I would argue that in fact there are no essential similarities (beyond "something becomes infinite"). I don't want to offend anyone, but here are the issues I see with this first section --

The examples have more to do with infinities than they do with singularities. Olber's paradox, the ultraviolet catastrophe, and the electron self-energy issue all result from adding up an infinite number of contributions, resulting in infinity, in a sense similar to a infinite series that doesn't converge. In these examples, there's a quantity that you compute at any point in space (total light from stars, energy density in blackbody radiation, energy in electron field) and it's infinity, everywhere. This isn't at all the same as the singularity in a black hole, for example, which is localized.

The only example that comes close, I think, is the electron one. Here you get one singularity comes from the fact that the potential energy of the electron-nucleus system would be infinite when the electron radiates away all of its energy and ends up in the nucleus (with everything considered as a point). You also get an infinite radiated energy. But the fact that point charges have infinite potential energy when they're sitting on top of each other is just regular, 19th-century electromagnetism and has nothing to do with quantum mechanics. Also the connection with gravity isn't clear.

There are also a few factual errors in the paragraph -- for one, the Pauli exclusion principle doesn't have anything to do with preventing the inspiral of electrons. It's true that it's related to electrons and atoms, which are also discussed in the paragraph, but the reason you don't get electrons spiraling in rapidly is not because of Pauli blocking. Secondly, you can "confine an electron in the space of a nucleus," or in any other finite region; you just get higher energy states for the electron (see square well). Finally, electrons do spiral into the nucleus in a manner perfectly consistent with quantum mechanics -- see electron capture.

The goal of making analogies to help the reader understand a gravitational singularity is admirable. But as it is, the intro paragraph talks about other historical problems in physics, then moves on to discuss things that aren't singularities (like problems with coordinate patches), and then concludes with talking about experimental tests of string theory. At this point, the reader's information about a gravitational singularity is still limited to the one-sentence intro at the top of the page.

So how about breaking this bit out onto another page, as Plumbago suggests? Wesino 15:35, 25 November 2006 (UTC)

[edit] Belief

I am still reluctant to believe that singularities exist, because of the zero demision problem. I am a theorist, it is hard for me to swollow things I can't see or imagine. maybe someone could point me in the right direction.-MJH 20:39, 8 October 2006 (UTC)

If the Universe was limited by what we can imagine or see, there wouldn't be a Universe at all.

The article argues that there are no singularities in physics, no matter what the math says.--Cherlin 10:17, 19 October 2006 (UTC)

The article says General Relativity shows both coordinate singularities in metrics, and absolute singularities wherever a point mass turns up in the equations, usually in considering the evolution of a Black Hole. Changing to a different metric disposes of coordinate singularities. Getting rid of the infinite density, infinite force of gravity, and infinite curvature of space around a point mass requires changes in known physics. (Simonapro 12:08, 24 October 2006 (UTC))

[edit] A question for the cosmologists

There's one thing I've never understood about black holes. It was explained to me years ago that as matter approaches the 'event horizon' (Schwartzschild radius or whatever you prefer to call it), time is distorted in the same manner that space is, and in fact for a particle exactly at the event horizon, time no longer passes as seen from this universe. There's a certain syncronicity to that explanation that makes me believe it's true. If so, then how does matter ever actually ENTER a black hole? It seems like it would take infinitely long for a particle to fall into a black hole, even as it continues being accelerated by the immense gravity (since of course space is distorted as well.) Even as the black hole is being formed, the density near the center would increase infinitely slowly, and I would think that no event horizon could ever actually form. The density would increase continuously, and would approach arbitrarily closely to the density necessary to form an event horizon, but never actually achieve or exceed that density. An observed black hole, then, would be nothing more than a collection of particles that are exceedingly close to, but not quite, dense enough to form a singularity. It truth there can be no event horizon in our universe for the simple reason that it would take literally infinitely long to form.

Crackpot enough of a theory? Middlenamefrank 21:37, 27 October 2006 (UTC)

Maybe but from another point of view how about this: A Black Hole consists of whatever material produces gravity (call it matter if you like) which has managed to exclude through the effect of gravity both energy and space (or distance when you break down the speed of light as a distance traveled over time). A Black Hole is then from this perspective the composite manfestation of absolutes, i.e., absolute temperature (zero) absolute energy (also zero owing to absolute zero temperature requiring absolute zero energy) and absolute time meaning that when you cross the event horizon you are no longer traveling - you are already there - all points within the event horizon are reached simultaneously when time within the event horizon is infinite and distance zero. Adaptron 12:31, 3 November 2006 (UTC)