# Talk:Black hole thermodynamics

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## Introduction

(William M. Connolley 17:31, 2004 May 26 (UTC)) Errrm... is this page dodgy? It starts off by saying that inside BH's classical thermo breaks down. Then it derives a pile of things using classical thermo. Then electrons go back in time.

I have no recollection of editing the intro; but I clearly did about six months ago. So you may rightly be suspicious of that bit. Charles Matthews 18:32, 26 May 2004 (UTC)

## Request for review

Requesting someone who is experienced in astrophysics looks over this article, becuase it's quite confusing and I'm not sure if it's all correct (September 2006) —The preceding unsigned comment was added by 86.133.225.32 (talkcontribs) on 23:02, 31 August 2006.

To whoever is willing to improve the article, here is a link to a review article: Don N. Page, Hawking radiation and black hole thermodynamics, New Journal of Physics 7 (2005) 203.[1].  --LambiamTalk 18:16, 29 October 2006 (UTC)
Thanks (although the link seems to be broken), I plan on improving this article sometime, only I can't say when. I have a copy of Wald's 1994 Quantum Field Theory in Curved Spacetime and Black Hole Thermodynamics, which I will use to clean this article (although I still like to find one more book). Later: --Sadi Carnot 19:38, 1 November 2006 (UTC)
Sadi, I recommend the book by Birrel and Davies: Quantum Field Theory in Curved Space. -Joshua Davis 23:01, 13 January 2007 (UTC)

Some sample calculations would be helpful, as the proper units to use are not obviouus to persons trained in other fields. ie mass in kilograms, distance in meters, gravity in meters per sec, per second k =? 12:02, 5 September 2007 (UTC) —Preceding unsigned comment added by Ccpoodle (talkcontribs)

## Proportionality

Shouldn't we say that the constant of proportionality is approximately 1/4, up to quantum gravity corrections, or is it somehow proven to be 1/4 regardless of what gravity looks like at Planck scale? Itinerant1 03:00, 12 January 2007 (UTC)--

There have indeed been cases studied where quantum corrections change it from 1/4. But this may be too technical to get into here. PhysPhD 06:42, 19 May 2007 (UTC)

## Deleted "Problems" sections

There may be some parts of these sections that could be salvaged, but they were way below the bar as they stood. All that stuff with waves and rolling dice was some author making stuff up.PhysPhD 06:42, 19 May 2007 (UTC) It was all quoted from Hawking sciam (not physical review) article, so i dont know ho you might consider it making stuff up, the work about the duality of time arrows comes from Santa Fe institute work done by gellmann and George west (nobel prize and ex-president of alamos lab), so it is not original research, the general view of relativity comes from Gravitation by Wheeler, i will repost latter a shorter version. I acknoledge english is not my first language, but also a need in this encyclopedia of better defined concepts - most people dont undestand its mathematics, and critical opinions (which is idfferent fro oroginal research). That is what the britannica and larousse have and wikipedia lacks because most students who work here tend to have limited knowledge to do those improvements, which however distinguish a truly good encyclopedia like those 2 - —Preceding unsigned comment added by 76.89.242.7 (talk) 01:10, 23 February 2008 (UTC)

## Black hole Evaporation?

The "laws of black hole mechanics" section lists dA > 0 as one of the laws, i.e. that black holes never decrease in size. Hasn't this theory been supplanted by the theory of black hole evaporation which allows black holes to shrink, and is in fact part of black hole thermodynamics? —Preceding unsigned comment added by 24.6.210.135 (talk) 07:51, 29 March 2009 (UTC)

Yes, that is correct. This law was disproved by Hawking. I guess the correct law is just dS/dt > 0, where the term ${\displaystyle kA/4l_{P}}$ is included in the expression for S. I will update the article with a note that this law has been superseded, but it would be good if someone with more knowledge of the subject and its history would take a closer look at this article and make it clearer.
(btw, pet hate: it should read dA/dt > 0, not just dA > 0, as the latter would imply that both dA/dt > 0 and dA/d(-t) = -dA/dt > 0, which is impossible) Nathaniel Virgo (talk) 14:36, 11 April 2010 (UTC)

Then dA/dt < 0 implies d(S_BH)/dt < 0 for BH evaporation, assumed to be a dissipative process. dA/dt < 0 either violates the second law or we assume that evaporation is not an irreversible process!

## Poor Quality

I am a chemist and fixed the parts on the page pertaining to thermodynamics. A lot of the definitions were sub par and the one for the 3rd law was flat out wrong. Whoever wrote this clearly has no training or grasp of thermodynamics. I do not know the quality of the astrophysics part, but from looking at it and reading other comments, this page is an unfortunate exception to wiki's very accurate scientific articles. Alchemist314 (talk) 09:34, 13 November 2010 (UTC)

As currently written, the part about the 3rd law is quite confusing, as it suddenly jumps from black hole thermodynamics to crystalline substances (which have nothing to do with black holes). ~ Peterwshor (talk) —Preceding undated comment added 13:13, 12 March 2011 (UTC).

## Simply Wrong

You don't need an astrophysicist to look at the article. It is completely wrong. If the entropy is proportional to the area then you don't need temperature. It exists at absolute zero, and the third law? The point that the area increases while evaporation decreases the area is well-taken. Evaporation by black-body radiation is complete nonsense. You need a thermal source to keep the walls of the cavity at a given temperature so that the radiation will be thermal at that temperature. If the black hole is the final state what would give rise to a finite temperature that would allow for thermal radiation? The zeroth law is also wrong. It say that when two bodies at different temperatures are placed in thermal contact they will arrive at thermal equilibrium at a common temperature. What does it mean for a black hole to have a uniform temperature? Is it possible for a gradient in temperature to exist? Temperature inversely proportional to the energy (mass) is also wrong. The entropy must be a concave function, i.e. a negative second derivative, not a convex function. Concave functions are to be maximized, convex functions minimized. The Bekenstein-Hawking expression is a convex function of the mass (energy), and, hence, it is not a candidate for an entropy at all. See arXiv:1110.5322v1 and http://www.youtube.com/watch?v=dpzbDfqcZSw for more detailed criticisms.Bernhlav (talk) 04:45, 26 December 2011 (UTC)bernhlav.