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What's Wrong With Black Hole Thermodynamics? 
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#1
Feb1612, 03:07 PM

P: 476

An interesting review of usual claims done in black hole literature by an expert in thermodynamics.



#2
Feb1612, 03:24 PM

Sci Advisor
PF Gold
P: 5,079

I've seen some other critical reviews of this. If I can find them, and they are in similar spirit, I'll post them here. [EDIT: Here is the abstract link: http://arxiv.org/abs/1110.5322 


#3
Feb1612, 05:28 PM

Emeritus
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P: 7,659

http://adsabs.harvard.edu/abs/1980PhLA...78..219L "Entropies need not to be concave"
seems to be in some disagreement about one of the major premises of the author. I stumbled over this while trying to see if the original paper was peer reviewed  I see other peer reviewed papers by the author, but I haven't found that the arxiv paper was ever published. Unfortunately the published papers mostly seem to require subscriptions to access. 


#4
Feb1612, 06:34 PM

P: 5,632

What's Wrong With Black Hole Thermodynamics?
yea, well Hawking thought Beckenstein was wrong as well....until Hawking arrived at Beckenstein's answer using a completely different approach.
Besides: It would be fun, though, if the cited paper above added new insights.....Anything there?? 


#5
Feb1612, 07:44 PM

Sci Advisor
PF Gold
P: 5,079




#6
Feb1712, 05:29 AM

P: 476




#7
Feb1712, 05:43 AM

P: 476

Well, he is a wellknown expert in thermodynamics, their works are cited by other thermodynamicians and his book in thermodynamics of irreversible processes is published by Dover classics. He has received Galilei Gold Medal 2009 The thermodynamics of endoreversible engines BH Lavenda  American Journal of Physics, 2007  link.aip.org Mean entropies BH Lavenda  Open Systems & Information Dynamics, 2005  Springer High temperature properties of the MIT bag model BH Lavenda  Journal of Physics G: Nuclear and Particle …, 2007  iopscience.iop.org ... It is difficult to believe that are not peer reviewed... 


#8
Feb1712, 05:45 AM

P: 6,863

The paper seems to be gooblegook. C_p is a derivative and can be be negative or nonexistent. He does a lot of equations based on the behavior of classical ideal monatomic gases, which I suppose merely shows that black holes are not made of classical ideal monatomic gasses.



#9
Feb1712, 05:47 AM

P: 6,863

He might be brilliant in thermodynamics in other fields, but the arguments that he is giving in that paper seems to be total nonsense. I may not be an "expert in thermodynamics" but I do know a thing or two about collapsed systems. His arguments make absolutely no sense because in any sort of stellar object, you are moving energy back and forth between the material object and the gravity field, and you can't just take an object and consider only the themodynamic energy. If you want to do your bookkeepping right, you have to consider the energy that is in the gravity field, which he doesn't do. Since he isn't including the energy in the gravity field, all of his other arguments fall apart. If you include gravity, you get the results in the first section, which he doesn't seem to understand. 


#10
Feb1712, 06:51 AM

Sci Advisor
PF Gold
P: 1,781

I note in the paper he also invokes a strong form of the 3rd law, [itex]\lim_{T\to 0}S = 0[/itex]. This form ignores residual entropy due to a degenerate ground state. He is here ignoring degeneracy.
His reasoning may be implicitly the "no hair" theorem but that doesn't apply. The very debate, whether BH's evaporate, is a question of observing "internal" degrees of freedom in the configurations of emitted thermal radiation (here "internal" to the surface configuration?). Reading the short paper, he is invoking analogue physical systems (partitioned volumes, ideal gasses) without any direct thought experiments about a BH per se. I don't see the paper pointing out any physical contradictions, only the exceptional behavior of BH thermodynamics. 


#11
Feb1712, 08:51 AM

P: 476

Effectively, nowhere he says or even suggests that black holes are made of "classical ideal monoatomic gasses". He uses the simple case of an ideal gas for illustrating the difference between c and C. 


#12
Feb1712, 09:01 AM

P: 476

Even if we ignore now that «the energy that is in the gravity field» is not welldefined in general relativity, what you say about thermodynamic energy and gravitation seems to be without any basis. Already many ordinary textbooks explain how gravitational energy [itex]M\phi[/itex] contributes to thermodynamic energy. Of course, in a BH the situation is more complex and [itex]M\phi[/itex] is not enough, but thermodynamics in presence of gravitation continues to hold and I fail to see your point. 


#13
Feb1712, 09:05 AM

P: 6,863

And in the case of black holes the physical material gets crushed to a singularity in a finite time leaving behind only the gravitational field whose thermodynamic properties are not constrained by the limits that constrain physical objects. Black holes are dominated by the gravitational field so if you add energy, the field will reconfigure itself, and that's what you are observe. The problem is that the author is used to laboratory thermodynamics in which you don't have to worry about the energy of the gravitational field, which works very badly when you figure out the thermodynamics of objects which are dominated by gravity. So in doing the energy calculations, he is completely ignoring gravity, which results in conclusions that are ridiculous. 


#14
Feb1712, 09:20 AM

P: 476

How do you adjust the 'exceptional behaviour' of evaporating BHs with the thermodynamic properties of the supposedly emitted thermal radiation? 


#15
Feb1712, 09:40 AM

P: 476




#16
Feb1712, 11:42 PM

P: 6,863

Also, a nonradiating star or black hole is a closed system. If you can come up with an argument in which you can argue that it's possible to talk about black holes while ignoring gravity, I'd like to hear it. 


#17
Feb1712, 11:58 PM

P: 6,863

Gravity changes everything. Once you have a gravitational field, then adding or removing energy from the system will cause interactions with the gravitational field, and *that's* what gives you heat capacities that you don't see in nonself gravitating objects. Black holes are not monoatomic ideal gasses. Because of selfgravitation, black holes are different enough so that you can't even use monoatomic ideal gasses as an analogy. 


#18
Feb1812, 01:40 AM

Sci Advisor
PF Gold
P: 5,079

Of interest to discussion of entropy of self gravitating systems is the following essay. Of particular interest is the discussion of gravothermal catastrophe  that self gravitating systems really have no equilibrium point short of a black hole.
This essay is not relevant to the core question of the validity of BekensteinHawking entropy. It takes that as a given, and argues that this is exceptional and not some natural limit of ordinary gravitational collapse processes. http://philsciarchive.pitt.edu/4744...nt_archive.pdf 


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