Tagged Questions
0
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3answers
236 views
Why isn't the Bekenstein-Hawking Entropy considered the quantum gravitational unification?
Based on the Bekenstein-Hawking Equation for Entropy, hasn't the relationship between quantum mechanics and gravity already been established.
5
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2answers
326 views
The Uncertainty Principle and Black Holes
What are the consequences of applying the uncertainty principle to black holes?
Does the uncertainty principle need to be modified in the context of a black hole and if so what are the implications ...
2
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1answer
136 views
What happens to atoms inside the black hole?
Black holes have very high gravitational force intending to crush everything. So as we know atoms in a molecule have inter atomic spacing between then and further electron,s also revolve at a certain ...
4
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1answer
88 views
Where and how is the entropy of a black hole stored?
Where and how is the entropy of a black hole stored?
Is it around the horizon? Most of the entanglement entropy across the event horizon lies within Planck distances of it and are short lived.
Is ...
1
vote
0answers
68 views
Black hole entropy from collapsed entangled pure light
Consider the following scenario, very similar to the one proposed in this question, but this time, the pure quantum radiation used for the black hole collapse, is now being split with down-converter ...
11
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2answers
404 views
Extremal black hole with no angular momentum and no electric charge
A black hole will have a temperature that is a function of the mass, the angular momentum and the electric charge. For a fixed mass, Angular momentum and electric charge are bounded by the extremality ...
4
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2answers
136 views
What is the motivation for assuming “Page” scrambling for Hawking radiation?
What is the motivation for assuming "Page" scrambling for Hawking radiation?
Obviously, at the semiclassical level, we want the outgoing Hawking radiation to look thermal and mixed. However, surely ...
1
vote
3answers
233 views
Why can't light escape from inside event horizon of Black Holes?
The simple answer: Its because Gravity of Black Hole there doesn't allow it. See also this and this Phys.SE posts.
Isn't it a classical answer? When we're unable to connect Gravity with Quantum ...
6
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0answers
87 views
Hawking radiation for closely orbiting black holes
Suppose we have two black holes of radius $R_b$ orbiting at a distance $R_r$. I believe semi-classical approximations describe correctly the case where $R_r$ is much larger than the average black body ...
2
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1answer
107 views
Why doesn't the firewall argument also apply to far away ingoing modes?
Gidom Mera's answer at http://physics.stackexchange.com/a/45511 is illuminating, but on closer analysis, it brings up further puzzles.
Backscattering works in both directions. Let's see what we get ...
11
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1answer
284 views
Quantum uncertainty of particle falling in black hole
A stationary observer at infinity sees a particle of mass m falling in a supermassive Schwarzschild black hole. He observes an increasing redshift and sees the particle ceasing to progress when it ...
5
votes
1answer
75 views
Is there a black hole interior in black hole complementarity?
According to black hole complementarity, for an external observer, the interior of the black hole is replaced with a stretched horizon at a Planck distance above where the horizon ought to be. Is this ...
0
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0answers
54 views
What is the physical mechanism for the subjective rapid vanishing of the firewall on such a short notice?
Suppose there is an astronomical sized black hole. There is an observer Alice. She jumps into the black hole after it has emitted 2/3 — or 3/4, the exact number doesn't matter — of all the ...
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3answers
306 views
An electron falling into a black hole
If an electron falls into a black hole. How can the Heisenberg uncertainty principle hold? The electron has fallen into the singularity now so it has a well defined position which means that it ...
1
vote
1answer
109 views
Information loss
First time poster!
I just burnt a piece of paper containing a 5 digit number I made up randomly and as far as I am concerned no one else will ever be able to retrieve the information contained on ...
0
votes
1answer
364 views
Firewall's grandfather paradox
See What are cosmological "firewalls"?.
Alice is in freefall in her spacecraft just above the horizon of a gigantic black hole. She measures whether or not the near modes of the horizon ...
8
votes
3answers
323 views
Thermodynamically reversed black holes, firewalls, Casimir effect, null energy condition violations
Scott Aaronson asked a very deep question at Hawking radiation and reversibility about what happens if black hole evolution is reversed thermodynamically. Most of the commenters missed his point ...
2
votes
1answer
149 views
what does holographic principle from string theory say about the possibilities of wormhole travel?
Is travel through stable macroscopic wormholes between remote points of spacetime going to be possible in a definitive theory of gravity, be it string theory or something beyond it?
Physicists level ...
3
votes
1answer
135 views
Formation of a black hole and Hawking radiation
From the perspective of an outside observer it takes infinitely long for the black hole to form.
But if the black hole is no extremal black hole, it emits Hawking radiation.
So the outside observer ...
1
vote
1answer
201 views
Special relativity paradox and gravitation/acceleration equivalence
One of the features of the black hole complementarity is the following :
According to an external observer, the infinite time dilation at the horizon itself makes it appear as if it takes an ...
2
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1answer
143 views
Black hole entropy
Bekenstein and Hawking derived the expression for black hole entropy as,
$$
S_{BH}={c^3 A\over 4 G \hbar}.
$$
We know from the hindsight that entropy has statistical interpretation. It is a measure ...
3
votes
3answers
574 views
Is it possible that QM is just GR?
The more I learn about General Relativity, the more it seems like it isn't fully understood. It seems that before it's full consequences were exhaustively understood, not 10 years after its discovery, ...
3
votes
2answers
227 views
Why isn't Hawking radiation frozen on the boundary, like in-falling matter?
From the perspective of a far-away observer, matter falling into a black hole never crosses the boundary. Why doesn't a basic symmetry argument prove that Hawking radiation is therefore also frozen on ...
3
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2answers
219 views
Hawking radiation and black hole entropy
Is black hole entropy, computed by means of quantum field theory on curved spacetime, the entropy of matter degrees of freedom i.e. non-gravitational dofs? What is one actually counting?
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1answer
52 views
Can anything come out from the big bang?
If any configuration of matter can fall into a black hole and hit the singularity, and ditto for the big crunch, and there is time reversal CPT invariance, does it mean anything can pop out of the ...
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votes
2answers
167 views
What is the mechanism for fast scrambling of information by black holes?
Sekino and Susskind have argued that black holes scramble information faster than any quantum field theory in this paper. What is the mechanism for such scrambling?
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1answer
153 views
Why are white holes the same thing as black holes in quantum gravity?
Why are white holes the same thing as black holes in quantum gravity? Their Penrose diagrams in semiclassical gravity are utterly different.
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2answers
124 views
Is the Chern-Simons integral of gauge fields over black hole singularities zero?
Suppose we have an evaporating black hole and a nonabelian Yang-Mills theory with a $\theta$ topological term. This counts the total number of instantons minus antiinstantons. Consider the total ...
2
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3answers
343 views
What happens to matter in extremely high gravity?
Though I am a software engineer, I have bit interest in sciences as well. I was reading about black holes and I thought if there is any existing research results on How matter gets affected because of ...
9
votes
5answers
966 views
How to get Planck length
I know that what Planck length equals to.
The first question is, how do you get the formula
$$\ell_P~=~\sqrt\frac{\hbar G}{c^3}$$ that describes the Planck length?
The second question is, will any ...
7
votes
1answer
203 views
Area law for Entropy in Loop Quantum Gravity
In connection with the long saga of the (claimed) microscopic
calculations of the Hawking-Bekenstein entropy in (3+1) Loop Quantum Gravity (LQG) and related approaches I have the following question: ...
1
vote
1answer
109 views
Classical black holes?
How big should the black hole be so we can consider it to be classical?
When they claim that we can not probe shorter distances than the Planck length, can it be true?
The argument says that, ...
5
votes
3answers
255 views
Information loss in a black hole
How does the Holographic Principle help to establish the fact that all the information is not lost in a black hole?
5
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3answers
204 views
From the perspective of an observer inside a black hole's horizon, where does the energy for Hawking radiation come from?
Would energy be seen to "flow" to the outside of the black hole? Through what mechanism?
3
votes
1answer
388 views
What happens to a photon in a black hole?
Assume a photon enters the event horizon of a black hole. The gravity of the black hole will draw the photon into the singularity eventually. Doesn't the photon come to rest and therefore lose it's ...
5
votes
1answer
158 views
Why are geons unstable? Are there other problems with geons?
I read in various places geons are "generally considered unstable." Why? How solid is this reasoning?
Is the reason geons are not studied much anymore because we can't make more progress without ...
1
vote
2answers
175 views
Could gravity hold electron charge together?
Could the gravitational force be what holds the charge of the electron together? It seems to be the only obvious possibility; what other ideas have been proposed besides side-stepping the issue and ...
3
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1answer
170 views
Could strings be geons?
Is it possible that string theory strings are geons? This may be an overly speculative or naive question, but is there an obvious reason why not? Both strings and geons seem to have roughly the same ...
38
votes
2answers
579 views
Analog Hawking radiation
I am confused by most discussions of analog
Hawking radiation in fluids (see, for example,
the recent experimental result of Weinfurtner et
al. Phys. Rev. Lett. 106, 021302 (2011), ...
5
votes
0answers
88 views
Geometric entropy vs entanglement entropy (dependent on curvature coupling parameter)
I have a quick question. In hep-th/9506066, Larsen and Wilczek calculated the geometric entropy (which I believe is just another name for entanglement entropy) for a non-minimally coupled scalar field ...
5
votes
2answers
190 views
Hayden-Preskill informational mirrors and decryption
I do have a question about an assumption made in the very interesting Hayden-Preskill paper of black holes as informational mirrors. Alice throws her top secret quantum diary which is $k$ qubits long ...
6
votes
2answers
246 views
How can one reconcile the temperature of a black hole with asymptotic flatness?
A stationary observer very close to the horizon of a black hole is immersed in a thermal bath of temperature that diverges as the horizon is approached. $$T^{-1} = 4\pi \sqrt{2M(r-2M)}$$ The ...
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votes
3answers
304 views
Incommensurability between different observers describing the same universe?
According to black hole complementarity, if there is a black hole and Alice falls into it carrying a qubit, but Bob stays out, then Alice can measure the qubit inside the black hole, and confirm it ...
3
votes
1answer
157 views
Please justify invoking logical positivism to causal patches and black hole interiors in quantum gravity!
Logical positivism is often invoked to explain why external observers can't talk about black hole interiors, or why we can't talk about what happens outside our causal patch in inflationary models. ...
7
votes
2answers
799 views
What happens when a black hole and an “anti-black-hole” collide?
Let's say we have one black hole that formed through the collapse of hydrogen gas and another that formed through the collapse of anti-hydrogen gas. What happens when they collide? Do they (1) ...
12
votes
3answers
782 views
Has the black hole information loss paradox been settled?
This question was triggered by a comment of Peter Shor's (he is a skeptic, it seems.) I thought that the holographic principle and AdS/CFT dealt with that, and was enough for Hawking to give John ...
2
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5answers
436 views
Black Hole Singularities
If two black holes collide and then evaporate, do they leave behind two naked sigularities ore? If there are two, can we know how they interact?
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6answers
1k views
The final death of a black hole
What are the different death scenarios for a black hole? I know they can evaporate through Hawking radiation - but is there any other way? What if you just kept shoveling more and more mass and ...
