Questions tagged [black-hole-thermodynamics]
85 questions
409
votes
8 answers
Did the Big Bang happen at a point?
TV documentaries invariably show the Big Bang as an exploding ball of fire expanding outwards. Did the Big Bang really explode outwards from a point like this? If not, what did happen?
John Rennie
- 367,598
57
votes
2 answers
Is the Hawking radiation of a charged black hole thermal?
Suppose you have a Schwarzschild black hole of mass $M$ and angular parameter $a = 0$ (no rotation).
Question: is it possible to throw a charge $Q$ at a faster rate than it will be re-radiated? Will the radiation profile be still thermal?
If it is…
lurscher
- 14,933
41
votes
3 answers
How much mass can colliding black holes lose as gravitational waves?
Concerning the recent detection of gravitational waves produced by colliding black holes, it has been reported that a significant percentage of the combined mass was lost in the resulting production of the gravitational waves.
So evidently in…
38
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2 answers
How does one correctly interpret the behavior of the heat capacity of a charged black hole?
Note: Although I have a provided an "answer" to the question, I did not resolve all the questions in this post satisfactorily. I invite anyone willing and able to provide a better answer, which I would be glad to accept instead.
Consider the…
Danu
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30
votes
4 answers
Is there a way to split a black hole?
Classically, black holes can merge, becoming a single black hole with an horizon area greater than the sum of both merged components.
Is it thermodynamically / statistically possible to split a black hole in multiple black holes? If the sum of the…
lurscher
- 14,933
20
votes
4 answers
Hawking radiation and reversibility
It's often said that, as long as the information that fell into a black hole comes out eventually in the Hawking radiation (by whatever means), pure states remain pure rather than evolving into mixed states, and "the universe is safe for quantum…
Scott Aaronson
- 2,492
19
votes
3 answers
Do black holes violate the first law of thermodynamics?
When a black hole absorbs matter is it destroying that mass, thereby destroying energy, therefore violating the first law of thermodynamics?
Neel Shah
- 325
18
votes
2 answers
Metric of an Evaporating Black Hole
The famous Hawking calculation is done with an assumption that the background is static, i.e. the evaporation doesn't change the mass parameter in the metric. Thus, we simply describe the geometry using the static Schwarzschild (or, generically,…
user87745
17
votes
3 answers
Why do larger black holes emit less Hawking Radiation than smaller black holes?
Pedestrian question from a non-physicist:
I read on Wikipedia that larger black holes emit less net Hawking radiation than smaller black holes.
This seems counterintuitive to me. If black holes are essentially sucking in mass and converting it to…
16
votes
4 answers
Why is black hole entropy not an extensive quantity?
The Bekenstein entropy for a black hole is proportional to the surface area $A$ of the black hole
$$
S_{BH} = \frac{k_B}{4 l_P^2} A
$$
with the Planck length $l_P = \sqrt{\frac{\hbar G}{c^3}}$.
The area is the surface of a sphere with Schwarzschild…
asmaier
- 10,250
13
votes
1 answer
Nothing falls into an evaporating black hole?
The Vaidya Metric is the metric that can be used to describe the spacetime geometry of a varying mass black hole. This metric reads
$$d\tau^2=\bigg(1-\dfrac{2M(\nu)}{r}\bigg)d\nu^2+2d\nu dr - r^2 d\Omega_2^2$$
For simplicity, I will assume…
user87745
13
votes
1 answer
Second Law of Black Hole Thermodynamics
I've been looking for a satisfying proof of this, and can't quite find it. I read the brief proof of the black hole area theorem in Wald, which is similar, but doesn't quite come down to the actual statement $\frac{dA}{dt} \geq 0$. I had pictured…
specterhunter
- 403
10
votes
1 answer
Another limit on the fine structure constant - based on a formula by Lubos Motl
This paper by Hod entitled "Gravitation, thermodynamics and the fine-structure constant" (PDF) starts from a formula on black hole resonance frequencies. If you follow the references through, Lubos Motl has also derived this formula in L. Motl,…
Gina Martelli
- 361
9
votes
2 answers
Is this derivation of Black Hole entropy viable?
This question is motivated by this one.
Suppose $l$ is the minimum measurable unit of length. What is entropy of a spinless particle contained in this interval?
We know that entropy of a two-level system depends on the probabilities of the…
Anixx
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9
votes
1 answer
What is the physical meaning of fact, that Reissner-Nordstrom black hole is thermodynamically unstable?
It is known, that Reissner-Nordstrom black hole is thermodynamically unstable [1].
Does it mean, that there is no Reissner-Nordstrom black hole in physical world?
Does it mean, that there may be phase transition?
Does it mean, that it can be stable…
drobnbobn
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