# Black hole versus 2nd law of thermaldynamics

1. Sep 12, 2009

### rcgldr

Does a black hole radiate infrared waves? If not, then it could absorb some of the infrared waves from a colder object, perhaps one orbiting the black hole, in apparent violation of the 2nd law of thermaldynamics.

2. Sep 12, 2009

### Staff: Mentor

3. Sep 12, 2009

### atyy

http://arxiv.org/abs/gr-qc/9912119
The Thermodynamics of Black Holes
Robert M. Wald
We review the present status of black hole thermodynamics. Our review includes discussion of classical black hole thermodynamics, Hawking radiation from black holes, the generalized second law, and the issue of entropy bounds. A brief survey also is given of approaches to the calculation of black hole entropy. We conclude with a discussion of some unresolved open issues.

4. Sep 14, 2009

### kwm

there is perhaps something else to consider to ponder, and yes what I say is controversial.

TdS=dE+PdV is the most common type of entropy change (dS)

If you consider that a blackhole is an isometric horizon (dV=0) into which matter and energy stream into, then you may ask yourself, should the second law (entropy increasing or constant) even apply.

Surely Dan Sheehan (prominent scientist) who has spent a long time pondering and writing about black holes and even challenging the second law seemingly does not subscribe to what I am saying. Even so it remains food for thought.

Kent Mayhew

5. Sep 15, 2009

### stevebd1

In black hole thermodynamics, the first law is relative to surface gravity (κ) and surface area (A) not pressure (P) or volume (V). The first law of bh thermodynamics (that deals with the mass/energy change, dM, when a black hole switches from one stationary state to another) is expressed-

$$dM= T_{\text{H}}\,dS_{\text{bh}}\,+\,\Omega\,dJ\,+\,\Phi \,dQ$$

where

$$T_{\text{H}}\,dS_{\text{bh}}=\frac{\kappa}{8\pi}\,dA$$

where TH is Hawking radiation $(T_{\text{H}}=\kappa/2\pi)$ and Sbh is entropy $(S_{\text{bh}}=A/4)$.

The first term (THSbh) is relative to irreducible mass- Mir=√(A/16π), the second to rotation- J and the third to charge- Q.

In respect of the second law of bh thermodynamics, through any classical process, the area of the event horizon does not decrease-

$$dA\geq 0$$

nor does the black hole's entropy, Sbh. The BH's event horizon area can remain stable in classical mechanics but will increase if mass is added or if spin or charge are reduced.

The second law of black hole thermodynamics can be violated if the quantum effects are taken into account, namely that the irreducible mass (and the area of the event horizon) can be reduced via Hawking radiation.

Sources-
http://edoc.ub.uni-muenchen.de/6024/1/Deeg_Dorothea.pdf pages 11-13

http://www.physto.se/~narit/bh.pdf [Broken] pages 9-12
(Table 2.2 on page 12 shows an analogy between the laws of thermodynamic and the laws of black hole mechanics)

Last edited by a moderator: May 4, 2017
6. Sep 15, 2009

### kwm

thanks for the quick reminder

However to me herein lay an example of an inherent problem in physics. You say that the simple does not apply, and perhaps you are right. Me I doubt it.

Things in this world are simple, heck even in blackholes. When you decide to take a prolonged complicated answer about something, you walk a dangerous path.

I will stick to my saying a blackhole is nothing but an isometric horizon. Hence to what extend does certain things apply become questionable.

You of course prefer the complicated answer. The beauty of such complications is that you can never nail down the argument because there are too many ways around it. Moreover if such an argument starts getting nailed, another complication is added. I have witnessed convoluted paths before and in one case I actually was able to prove a simpler explanation existed, using someone else's empirical data that was considered to be unexplainable.

Do I subscribe to Hawkins radiation, well to be honest I sit on the fence why because it takes one such a convoluted path to get there. Especially when other simpler arguments exist.

All the best Kent

7. Sep 24, 2009

### JoeDonlan

I agree that simple is better as Ockham's Razor supports...here, at a high level, is my take on black holes:

As most know, black holes are a prediction of Einstein’s GTR. In simple terms, if a star is large enough—about a magnitude or greater than our Sun—after it exhausts its energy from nuclear fusion, it will likely implode upon itself. If that happens, the gravitational field it emits (as it occupies a smaller and smaller region of space) will eventually become so great that it will suck everything into it, including its own emitted EM radiation. Imagine an imploding star of this magnitude as a huge vacuum cleaner in space sucking everything into it, from nearby and far away as even light from very distant stars will disappear into it. Einstein's equations further suggest that everything eventually will fall into a point that has no volume and is, by definition, infinitely dense; hence physicists call it a singularity. At this point, the laws of physics break down, as we don’t have laws to explain this event and/or what happens next.

In my theory a black hole is the precise alter ego of the reality we witness and the world we experience. We perceive space and sense time in a linear fashion. A black hole is the antithesis of this. It evaporates space-time. It essentially runs the universal clock backwards. A black hole is, in effect, an anti-star. Stars are emitters; black holes are absorbers. Although the effects are the same, to state that light does not escape a black hole is highly misleading. Black holes do not emit light [or other forms of EM radiation]; they absorb it. Stars exist until they exhaust their hydrogen; therefore, they have finite lifetimes. Black holes exist for all time; i.e., as long as there is time and space available to fuel them. Stars, one could argue, are the engines that effectively spew out time and space. Black holes are the engines which suck in time and space. When there is no more time and space to fuel the black holes, they will explode, creating a new beginning of time and space.

Hawking suggests that matter can escape from black holes by quantum effects; consequently, a black hole can evaporate. I disagree. Time and space run backwards in a black hole; it’s a one-way street. There is no condition in which a black hole will stop sucking in time and space as long as time and space exist.

It is thought that the opposite of a black hole is a white hole. It is assumed that white holes emit matter and EM radiation [from the singularity]; thereby making them the time-reversal of a black hole. I contend that white holes are needlessly complex, and we do not need to invent them. I propose that garden-variety stars in the heavens are the precise opposites of black holes. If you were to film a star and then run the film backwards [keeping in mind that most physical theories are independent of the direction of time] you would, using the term loosely, witness the effects of a black hole. We haven’t found evidence of exotic white holes because they do not exist…they are simply stars.

The pure elegance and symmetry of this model is its allure. Stars create EM radiation, black holes absorb it. Stars create space-time with their emitted energy; black holes absorb space-time. Eventually, when stars die out and cannot create more space-time; black holes will morph from absorbers to emitters and create new universes and start time and space anew.

8. Sep 25, 2009

### kwm

I appreciate that your ideas are following the old KISS principle. Which is grand. And although I am only a casual reader of this tsuff, I am not thrilled with some of the quantum arguments, nor Hawkins radiation.

But when you argue time goes backwards, are you not also basing it on assumptions. It is sort like entropy being the arrow of time but now things are reversed. By the way I am not thrilled with entropy and arrow of time arguments, but no matter that just a me thing.

Cheers

9. Sep 26, 2009

### Skolon

The idea of mr. JoeDonlan is interesting but I think is wrong.
A BH can't be "the opposite" of a star just because it is a gravitational object exactly as a star. To be a "minus-star" it must be an antigravitational object, and obviously it is not.

Please, let me ask something else about BH. What is happening with kinetic energy of falling matter? For the outside Universe doesn't exist any collision, so the kinetic energy of falling matter never transfer to BH. On the other hand, when matter fall through the event horizon this energy stop to exist for the outside Universe. It is simple disappare. At the Universe scale the total amount of that lost kinetic energy must be very significant. I'm not a specialist, so please be kind and tell me what the "official science" are saying about that.