Talk:No-hair theorem

message: I would like to opine that the title is wrong! The no hair "conjecture", or whatever you want to call it, is not a theorem. A theorem is something you prove. Once you prove it, it is true. The uniqueness theorems are theorems. The only stationary black hole solutions in electro-vacuum Einstein-Maxwell are the the Kerr-Newman class. That's a theorem. Read Heusler's book. You can't have counterexamples to theorems, you can only have examples that have different assumptions. The Einstein-Yang-Mills, Einstein non-minimally couple scalar field etc solutions are counterexamples to the no hair "conjecture" but don't violate the uniqueness theorems. Theorems don't fail by definition (unless someone made a booboo).--Eujin16 (talk) 02:01, 24 March 2008 (UTC)
replies: text: I think this confusions reflects a confusion in the article.  AIUI the NH theorem was made in the context of GR, and within that domain it is pretty well proven, isn't it?  cf Price's theorem (no relation) It seems people don't expect the NHT to hold within quantum gravity or a theory of everything; to that extent the so-called counter examples seem rather besides the point. --Michael C. Price talk 17:00, 19 February 2009 (UTC)
thread_title:  Title query 

message: This sentence makes no (or very little) sense, but I don't feel qualified to make any amends (First para):
:All other information about the matter which formed a black hole or infalling into it, "disappear" behind the black-hole event horizon and are therefore permanently inaccessible to external observers.
First of all, 'information' is singularis, so it should be 'disappears', but 'infalling'? Could someone knowledgeable fix it? Asav 13 Dec. 2005
Igorivanov 14:24, 23 Jul 2004 (UTC)
thread_title:  Language query 

message: If the surface of a black hole has entropy S, doesn't that imply that the event surface is in one of (1/k) exp (S) microstates at a microscopic level, just by inverting S = k ln W ?   
Why should the fact that its macroscopic properties are determined completely by the no hair theorem worry us any more than any other thermodynamic object which has a well-defined macrostate, but is in an unknown one of many possible microstates ?   What is the big problem here ?  -- Jheald 22:48, 2 November 2005 (UTC)
thread_title:  Microstates and macrostates ? 

message: Since volume doesn't depend on mass, charge, or spin, does the No-Hair Theorem state that black holes have zero volume, or that they all have identical volume, or what? ---63.26.160.105  02:19, 2 February 2006 (UTC)
replies: text: Well, volume doesn't really make sense in this context.  See for example the discussion of the so-called Einstein-Rosen bridge (wormhole of a kind) in the discussion of nonrotating black holes modeled by the Schwarzschild vacuum solution in MTW, Gravitation; see General relativity resources for full citation.  On the other hand, you could ask for the area of the event horizon.  This has no immediate physical meaning but it is mathematically well defined and has a profound meaning in terms of the global structure of a black hole spacetime.  Then the brief answer to your question is that it can be computed in terms of the parameters mentioned in the no hair theorem.  See for example Frolov & Novikov, Black Hole Physics (full citation given in the article just mentioned). ---CH 03:16, 2 February 2006 (UTC)
thread_title:  What about volume? 

message: I believe I read in one of Kip Thorne's books that John Wheeler coined the term: "Black holes have no hair." Is this correct?  David618 02:52, 12 March 2006 (UTC)
replies: text: Yes.  The book was no doubt Black Holes And Time Warps : Einstein's Outrageous Legacy, a popular book which contains many anecdotes about the Golden age of general relativity. ---CH 16:45, 14 March 2006 (UTC)

text: yes. --Michael C. Price talk 17:01, 19 February 2009 (UTC)
thread_title:  John Wheeler 

message: I edited earlier versions of this article and had been monitoring it for bad edits, but I am leaving the WP and am now abandoning this article to its fate.  And WikiProject GTR is presumably defunct.
Just wanted to provide notice that I am only responsible (in part) for the last version I edited; see User:Hillman/Archive.  I emphatically do not vouch for anything you might see in more recent versions, although I hope for the best.
Good luck in your search for information, regardless!---CH 02:28, 1 July 2006 (UTC)
thread_title: Students beware

message: I don't understand why this theorem explicitly states that black holes retain mass and angular momentum but says nothing about  normal, linear momentum.  I suppose it's considered obvious to an expert in the field? I can't imagine that a rapidly moving star ceases to move when it collapses in to a black hole (as if there were some coordinates throughout the universe such that non movement could even be defined).  If I wanted to characterize a black hole COMPLETELY,  I would need one number for mass, one signed number for charge, one 2 vector for direction of movement and a scalar for magnitude of movement, and one two vector for axis of rotation and a scalar for speed of rotation.  Is that correct?
:Momentum isn't considered a property of the black hole as it depends on reference frame. We only consider the frame-independent magnitude of the momentum, which is the mass. (Similarly, we only consider the magnitude of the angular momentum as a property, but not the direction) Ben Standeven 23:34, 29 November 2006 (UTC)
thread_title:  What about Momentum (non angular)? 

message: http://arxiv.org/abs/gr-qc/0702006
"No hair theorems for positive $\Lambda$"
which starts off:
:"We extend all known black hole no-hair theorems to space-times endowed with a positive cosmological constant $\Lambda.$ "
seems to extend the non-hair theorem for black holes to universes which have a cosmological constant.--Michael C. Price talk 02:11, 1 July 2007 (UTC)
replies: text: I discuss a recent analytic proof of bypassing the no-hair conjecture for two interesting (and quite generic) cases of four-dimensional black holes: (i) black holes in Einstein-Yang-Mills-Higgs (EYMH) systems and (ii) black holes in higher-curvature (Gauss-Bonnet (GB) type) string-inspired gravity. Both systems are known to possess black-hole solutions with non-trivial scalar hair outside the horizon. The `spirit' of the no-hair conjecture, however, seems to be maintained either because the black holes are unstable (EYMH), or because the hair is of secondary type (GB), i.e. it does not lead to new conserved quantum numbers.
which also seems relevant. --Michael C. Price talk 02:19, 1 July 2007 (UTC)
thread_title: Cosmological constant

message: Is this "black holes have no hair" statement related to the "hairy ball" observation?  A "hairy ball" (e.g. the physiscist's standard spherical vacuum-racing hamster) cannot have all of the hair smoothed down perfectly flat. In at least two points ("boojums" if you'd like more physics-related neologisms) the hair must either come to either a radial point, or a point of extreme curl. As such points aren't observable from outside the event horizon, we can infer that there's no "hair" on a black hole, where this "hair" analogy can be extended to a number of forms of possible "texture" in its surface. Andy Dingley (talk) 11:15, 15 April 2008 (UTC)
replies: text: sorry for reviving this old discussion, but given that this is not the first mention of this apparent similarity, i thought i'd revive the discussion. what do you guys think about the issue? couldn't we relate the "hair" (information) about the matter that created, and is absorbed by, the event horizon of the black hole to the properties of the tangent space (i.e. derivative)? sorta spitballing obv, but it sure seems i'm not the only one who sees a potential relationship that may be worthy of further discussion.174.3.155.181 (talk) 17:55, 2 July 2016 (UTC)
replies: text: I don't understand what you're talking about. Please elaborate. I'm also going to remove the RfC template, since there's no RfC question (or if there is, it's not easily understood). Banedon (talk) 01:58, 19 July 2016 (UTC)
thread_title:  Hairy Ball Observation 

message: Is the final word supposed to be 'isentropy' and not 'isotropy'?  I thought we were talking about entropy, and not space...
128.171.31.11 (talk) 02:27, 30 April 2008 (UTC)
thread_title:  Classical/Quantum Entropy 

message: Surely a hypothesis that the black hole is stationary should be included in the first sentence. I think a hypothesis that the space-time is real analytic is also necessary. 130.237.201.40 (talk) 14:30, 21 October 2008 (UTC)
thread_title:  Hypotheses 

message: This is a long, uncited section, and it seems to me that it is mostly unrelated to the article topic. --192.75.48.150 (talk) 15:51, 3 April 2013 (UTC)
replies: text: It appears to be a theoretical argument that the no-hair theorem is not strictly true at a quantum level, but is merely a classical approximation. As such, it is relevant to the article. But it would be nice to have a reference for it. JRSpriggs (talk) 08:11, 4 April 2013 (UTC)
thread_title:  "Black holes in quantum gravity" section 

message: Is there any intuitive way of understanding why a magnetic moment is not possible? Given tthat a charge is possible, and that angular momentum is possible, plain-old gut sense suggests that a magnetic dipole moment should be possible. I can think of hand-waving arguments to banish higher-order magnetic moments, but not the dipole.  But surely, there is a way to do this? 67.198.37.16 (talk) 21:56, 30 July 2015 (UTC)
replies: text: Magnetic dipole moment in fact equals (charge / mass) × (angular momentum), see equation (33.10) on p. 892 in Misner, Thorne, Wheeler "Gravitation" (), so it must be non-zero for electrically charged rotating black holes. — Mikhail Ryazanov (talk) 18:20, 23 July 2022 (UTC)
thread_title:  Magnetic dipole moment? 

message: There's a new publication about "soft hair" on black holes retaining some of the information: http://physics.aps.org/articles/v9/62.
Could someone with more knowledge of the subject than me please edit that in?
2A02:810D:14C0:5A0C:20B7:15AE:50A5:C945 (talk) 21:06, 8 June 2016 (UTC)
replies: text: The article already mentions "excepting quantum fluctuations". JRSpriggs (talk) 01:16, 9 June 2016 (UTC)
thread_title:  Recent publication - soft hair 

message: I guess, the "theorem" conditions should state that it is limited to isolated black holes in equilibrium. Because, for example, when two black holes merge to form a single black hole, this non-stationary solution has more degrees of freedom than just the total mass, charge and angular momentum (see ). Or when something falls into a black hole, it also breaks the BH symmetry and creates "ripples" on its event horizon (leading to radiation of gravitational waves as the BH equilibrates). — Mikhail Ryazanov (talk) 05:00, 12 January 2020 (UTC)
thread_title:  Limitations 

message: The article explains the "results" of the theorem, ie what the theorem states, what the implications are. But what is the rationale behind the conjecture? How was it derived? For example "why" wouldn't it make a difference if the black hole was composed of matter or antimatter?Feldercarb (talk) 01:04, 15 July 2022 (UTC)
thread_title:   How or Why?