# Talk:Cosmic censorship hypothesis

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## Cheap conjecture

"The fundamental concern is that, since the physical behavior of singularities is unknown, if singularities can be seen from the rest of spacetime, physics may be unpredictable." Is there any other foundation for this conjecture, or is it just a case of "this situation (naked singularities existing) causes trouble, so we just conjecture it can't happen"? I'm not a physicist, but it sounds a bit cheap to me. :) -- Schnee 14:25, 9 Jun 2004 (UTC)

There is no mathematical reason to say that naked singularities cannot exist. In fact, mathematically, solutions which contain naked singularities are well known. for example, the Kerr solution (for certain regions of parameter space) has a naked singularity in the shape of a ring. Physically however, naked singularities are problematic. in particular, causality may breakdown, and closed timelike curves may exist. this is what is meant by the phrase "physics may be unpredictable". So physically, we can say that we don't want naked singularities to exist, because it would cause trouble. This is a cheap way out, as you say. But that's why the Cosmic Censorship Conjecture was formulated, so that something based on physical intuition could be replaced by a mathematical proof. There is some evidence that those solutions with naked singularities, like the Kerr solution are not physical. I don't know the details, but i think it is something along the lines of the statement that the solution will end up not being stable against perturbations, and therefore we can expect that it would never arise in the real world, even if it is a mathematical solution.
I did a little googling, and found this nice quote about the possible failure of the Cosmic Censorship Conjecture:
"It is well known [...] If it does not hold, then the formation of a naked singularity during collapse would be a disaster for classical general relativity theory. In this situation, one cannot say anything precise about the future evolution of any region of space containing the singularity since new information could emerge from it in a completely arbitrary way." - Shapiro & Teukolsky, PRL, Vol 66, No. 8, Feb 1991.
I would like to see a little more about this result. I only know the Kerr result, the only thing i can find in the textbooks is this brief quote from MTW
"Naked singularities could influence the evolution of the external universe; and, therefore, unless one knew the lasw of physics governing singularities-- which one does not-- they would prevent one from predicting the future in the external universe"
Anyway, if you think that there should be something more precise in the article than "physics may be unpredictable", then i fully agree. Lethe 21:21, Jun 16, 2004 (UTC)
I do think it would be nice if the article would be clearer on this, but unfortunately, I lack the knowledge to rewrite it. Thanks for your explanations, though - they were quite enlightening. I'll see if I can find more about this (and in particular, more about physical reasons why the CCH should hold true, as opposed to the "meta-reason" of it not holding being problematic). -- Schnee 21:45, 16 Jun 2004 (UTC)

## True or False?

the article says "In 1991, John Preskill bet against Stephen Hawking and Kip Thorne that the hypothesis was true. He won the bet (for an encyclopedia of the winner's choice) due to the discovery of the special situations just mentioned."

now, those things mentioned above provide counterexamples to the hypothesis. so if Preskill bet that the hypothesis was true, then those counterexamples lost him the bet, so which is it? did he win the bet, or did he bet that the hypothesis was false?

Or am I just being stupid and reading this wrong? Lethe 00:29, Jun 16, 2004 (UTC)

I think I edited it to its current version, and I got my information from the bet itself:
http://www.theory.caltech.edu/people/preskill/info_bet.html
I think your version is right. Maybe I had the conjecture switched around in my head. Double check it. - Omegatron 01:54, Jun 16, 2004 (UTC)
Well, it seems to me that the bet described in the article is only indirectly related to the bet in the link. ostensibly, one is about the existence of naked singularities, and the other is about information loss in Hawking radiation. i think they really are the same bet, or at least related, but the precise description in which they are the same is beyond me. Something like this: if the cosmic censorship principle holds, then a singularity must be surrounded by a true event horizon, past which no information can flow. thus a pure quantum state must evolve to a thermal state when it Hawking radiates. If, on the other hand, we want to preserve unitarity in our quantum theory, we should require that a pure state evolve to a pure state, which i guess would imply that it's not a true event horizon, as we understand them from classical GR (this is the part i am foggy on). So i guess in some sense this would a sort of weak violation of the Cosmic Censorship Principle.
So Preskill bet that the cosmic censorship principle was false in the original bet in 1991, and then in 1997 he bets that it is true that pure states evolve to pure states. I don't know the history, but this is what i infer from the article text and the bet that is currently up on Preskill's webpage. It would be helpful if we could find a link to the original 1991 bet, to get this all straightened out.
Incidentally, I think Preskill is going to win again (and there is some evidence that he has already). perhaps we should add some stuff to the article to reflect some news about the 1997 bet.
- Lethe 12:49, Jun 16, 2004 (UTC)
Compared to you, I know nothing about it. Definitely add some more information if you know it. Here is the site with the bets, however. I'm still good for somethin':
http://www.theory.caltech.edu/people/preskill/bets.html - Omegatron 13:56, Jun 16, 2004 (UTC)
OK, actually that linked pretty much cleared everything up for me. Basically, there are two bets, one about information loss, and one about the nonexistence of naked singularities. the first one is still open, the second one was won by Preskill, and then reformulated to make it less susceptible to technicalities, and is open again. While there may be some vague relationship between the two concepts that i alluded to above, i don't really understand that connection, and perhaps there isn't one. Therefore the information loss bet doesn't belong in this article (but certainly deserves its own article!) Lethe 21:24, Jun 16, 2004 (UTC)

A perfect Stephen Hawking quote: "God abhors a naked singularity", in other words, were humans able to witness the birth of the universe as per the "Big Bang" theory, it would be the best example of a naked singularity. —Preceding unsigned comment added by 96.50.10.211 (talk) 04:11, 19 May 2010 (UTC)

## Strong vs. Weak

I think we should make explicit the two different version of the Cosmic censorship principle

There you go with an initial revision. -- Schnee 23:07, 16 Jun 2004 (UTC)

## Closed timelike curves etc.

Can someone explain how the existence of a naked singularity may lead to a loss of causality, existence of closed timelike curves or other such things? And, for that matter, is that the existence of a naked singularity *might* lead to it, or *would* it definitely? Thank you. ^_^ -- Schnee 16:01, 17 Jun 2004 (UTC)

I second this request. Perhaps it's just my layman's lack of understanding of the nature of singularities, but a clearer explanation of why there would be a loss of causality would be nice, because it doesn't seem obvious from the text. -- Tsuji 03:00, 21 May 2007 (UTC)

## Hawking changes his mind

Is this relevant? -- Schnee 19:37, 15 Jul 2004 (UTC)

Yeah, I think so. Here is another one: [1]. I don't know enough to put it into the article, and we might as well wait til the 21st to hear the whole story anyway. - Omegatron 17:35, Jul 16, 2004 (UTC)

## Is it false now?

Naked Singularity says:

Computer simulations of the collapse of a disk of dust have indicated that these objects can exist, and thus the Cosmic censorship principle (stating that singularities are always hidden) does not hold. Stephen Hawking lost a bet about this question.

I'm not sure what to make of that; it seems to be related to the following from this article:

Computer models of gravitational collapse have shown that naked singularities can arise, but these models rely on very special circumstances (such as spherical symmetry). These special circumstances need to be excluded by some hypothesis.

For a casual reader without a background in physics (such as me), the way the articles are worded at the moment is suboptimal, though; Naked Singularity seems to imply that we do know (or at least are reasonably sure) that naked singularities do in fact exist in the universe, while this article makes it seem like the fact that they arise in the aforementioned computer models is a technical issue that only stems from the fact that the current models are still overly simple, and that we do NOT know whether naked singularities do exist "in the wild" or not. Can someone who has a background in physics please clear that up and reword the articles accordingly? Thanks a bunch. :) -- Schnee (cheeks clone) 20:56, 18 August 2005 (UTC)

## Determinism

I've restored the paragraph about determinism.

First of all, classical GR in the absence of naked singularities is at least locally deterministic. See Wald, for example.

References to quantum mechanics don't make much sense in context of this article, because cosmic censorship hypothesis is essentially a classical concept.

Finally, saying that QM is non-deterministic is not accurate. If we know the wave function and the hamiltonian of the system at any given moment of time, we can predict its evolution.

See [2] for a brief discussion of determinism in GR. --Itinerant1 22:27, 19 June 2006 (UTC)

Maybe a qualifying statement, like "statistically deterministic" would be helpful. While on quantum level it's non-deterministic (not fully deterministic is still non-deterministic), the emergent macroscopic properties are fully predictable to within statistical error. 83.14.232.226 (talk) 09:39, 23 October 2015 (UTC)
I added ",as described by the general theory of relativity," as a clarification tho the paragraph about determinism. I also added a reference to a nice book chapter about determinism in physics by John Earman. He analyzes how deterministic the various physical theories really are and concludes: "In Newtonian theories determinism is hard to achieve without the aid of various supplementary assumptions that threaten to become question-begging. For special relativistic theories determinism appears so secure that it is used as a selection criterion for “fundamental fields.” GTR, under the appropriate gauge interpretation, is deterministic locally in time; but whether it is deterministic non-locally in time devolves into the unsettled issues of cosmic censorship and chronology protection." Thawn (talk) 10:50, 4 December 2015 (UTC)

## Quantum

Is quantum behavior the result of an "event horizon" surrounding something of zero mass, just as an event horizon surrounds the black hole of "infinite mass"? 12.41.40.20 18:00, 4 January 2007 (UTC)

## Mathematical conjecture or physical conjecture?

Apropos of the recent edit to the introduction: are these mathematical conjectures, or conjectures about what's actually out there in the physical world? It's not clear to me from the article at present. -- Spireguy (talk) 14:25, 11 April 2008 (UTC)

The conjectures are mathematical, in the sense that they can be given precise and rigorous definitions. Since general relativity is a physical model, they are also conjectures about the physical world and in particular, it should be clear that the original motivations came from physics.
I wanted to emphasize the mathematical side, because their is no way to study the conjectures in a way which is non rigorous. For instance, in physics, one often assume that all functions are regular (smooth) or that certain terms can be neglected compare to other ones. Here, the conjectures are statements about the regularity and the behavior of the solutions for late time. Therefore, one need to be very careful with the assumption on the regularity, or when comparing different terms in the equations, because one term might well become large, only after a very large time.
There has been (and there is still) lots of confusion in the literature which is why I am trying to make the page more precise, accurate and up-to-date.J.smulevici (talk) 20:13, 24 April 2008 (UTC)j.smulevici

## Quantum mechanics

Isnt it in the nature of quantum mechanics, (and einsteins physics as well) that location and speed cannt be observed at the same time. We never know where and at how many places a quantum particle apears (even looking at it would change its position, think of the boudble split experiment). So how can one still think of a universe which is deterministic ? —Preceding unsigned comment added by 82.217.115.69 (talk) 08:42, 6 October 2008 (UTC)

## page says merge / merge box removal

There is an "it has been suggested that ... merge" box on the main page, but no corresponding setion on the talk page. Where is the discussion? 68.144.80.168 (talk) 16:04, 25 June 2008 (UTC)

I'd say the discussion is right here, and it's a slow one. OPPOSE - I found this article looking for "Naked singularity. Taking over a year per comment suggests there's no consensus to merge, and I suggest the merger box be removed. --Smoggyrob | Talk 16:32, 13 February 2010 (UTC)

## future null infinity -- entry

Please? And delete this when done... — Preceding unsigned comment added by 84.231.0.235 (talk) 16:21, 18 October 2012 (UTC)