A black hole is a volume from which photons, or any matter, can not escape. More formally, the coordinate speed of light at the event horizon - the boundary of a black hole - is zero, as measured by a sufficiently separated observer.
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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, ...
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37 views
Relation between maximum entropy thermodynamics and entropy bounds
Here is a question which I've been thinking about, I'm sorry if it's little too vague, maybe you could point me to some source to read, if there's no clear direct answer.
The whole concept of ...
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367 views
Collision between Neutron stars and Black holes
When two neutron stars or black-holes come closer and closer, their angular velocity increases with decrease of distance and they start to revolve around a constant center with high relativistic ...
3
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1answer
248 views
Reasons to suspect that matter is emitted from black holes nonthermally
Quote: "One has reasons to suspect that this matter is emitted from the black hole nonthermally, more or less as it came in, after doing a traversal of the interior regions." Ron Maimon in Do black ...
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64 views
Kaluza Klein Particles and Mini Black Holes
Are the Kaluza Klein Particles and Mini Black Holes associated with the ADD and Randal-Sundrum models different names for the same class of particles or are they distinct.
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2answers
213 views
Do black holes accelerate in spin as they obtain more mass?
It is known that - When a star collapses during the formation of the black hole, the black hole obtains the spin of the star which it collapsed from...
What I'd like to know is, If this spin ...
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216 views
Black-holes are in which state of matter?
Wikipedia says,
A Black hole grows by absorbing everything nearby, during its life-cycle. By absorbing other stars, objects, and by merging with other black-holes, they could form Super massive ...
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Maximal kinetic energy due to gravitational attraction
Two related questions:
Small object of mass $m$ is falling into the supermassive black hole of mass $M$. What is the maximal kinetic energy can be acquired by the small object, from the point of ...
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96 views
Angular momentum of a rotating black hole
Is there an upper limit to the angular momentum of a rotating (Kerr) black hole?
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127 views
Is it possible for a black hole to form for an observer at spatial infinity?
To my knowledge if you calculate the coordinate time (time experienced by an observer at spatial infinity) it takes an infinite amount of time for an object to fall past the horizon of a Schwarzschild ...
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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 ...
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2answers
245 views
Why do photons add mass to a black hole?
Why do photons add mass to a black hole?
When photons are taken irreversibly into a black hole does the mass of the BH increase?
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51 views
How can black holes have gravity? [duplicate]
Possible Duplicate:
How does gravity escape a black hole?
How can gravity get out of a black hole? If a black hole is so powerful that even light does not travel fast enough to get out, and ...
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199 views
black hole event horizon
Given gravitational time dilation, under what conditions will a test particle cross an event horizon before the black hole evaporates? Assume zero background radiation.
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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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1answer
98 views
how does nature prevent transient toroidal event horizons?
.. and does it really need to?
Steps to construct a (transient) toroidal event horizon in a asymptotically flat Minkowski spacetime:
1) take a circle of radius $R$
2) take $N$ equidistant points in ...
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722 views
What is the escape velocity of a Black Hole?
The escape velocity of Earth is $v=\sqrt{\frac {GM}{R}}$, where $M$ is the mass of the Earth and $R$ it's radius (approximating it as a sphere), and is much less than light speed $c$.
What is the ...
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133 views
event horizons are untraversable by observers far from the collapse?
Consider this a followup question of this one
In the classical schwarszchild solution with an eternal black hole, the user falls through the event horizon in finite local time, but this event does ...
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166 views
Where 2 comes from in formula for Schwarzschild radius?
In general theory of relativity I've seen several times this factor:
$$(1-\frac{2GM}{rc^2}),$$
e.g. in the Schwarzschild metric for a black hole, but I still don't know in this factor where 2 comes ...
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262 views
Hawking radiation from point of view of a falling observer
This paper tells that Hawking claimed that the falling to a black hole observer will not detect any radiation. But only because the frequency of the Hawking radiation will be of the order $1/R_s$ so ...
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Will the Big Rip tear black holes apart?
There seems to be an obvious contradiction between the predictions of the physics of black holes and the Big Rip, a predicted event about 16.7 Gyr in the future where local groups, galaxies, solar ...
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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
59 views
Is mass of the parent star is equal to the mass of the born blackhole
I want to know whether mass of the black hole which has born from a star is similar to its parent star or not. whether the born black hole will have high or low mass comparing to its parent star. ...
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109 views
State of the entangled particles at the event horizon of black hole
Looking through the article of Samir Mathur http://arxiv.org/abs/0909.1038
he assumes that the entangled particles created at the event horizon have all the state ...
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1answer
152 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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1answer
194 views
What is the speed for an object that travel close to the speed of light?
I have some questions regarding Einsteins theory of Relativity that should be fairly easy to answer. Lets say we make an experiment where we have a rocket (with an astronaut inside) that travels very ...
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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 ...
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Does black hole complementarity apply to white holes?
If physics is time reversal invariant, there ought to be white hole complimentarity as well. Imagine a white hole so enormous that it is possible for life to evolve entirely within it for billions of ...
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193 views
Falling into a black hole
I've heard it mentioned many times that "nothing special" happens for an infalling observer who crosses the event horizon of a black hole, but I've never been completely satisfied with that statement. ...
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1answer
157 views
Are “typical” black holes rotating, or stationary?
From my (somewhat limited) understanding of GR I know that there are two different kinds of solutions that produce a black hole, some that rotate and some that do not. What I can't figure out from my ...
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110 views
How can things at the event horizon slow down and appear to stop to a remote observer?
So they say the remote observer will never see anything fallen to the black hole, because any object will slow down as it gets closer to the event horizon and eventually stop to stay there forever. Am ...
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1answer
117 views
geometry inside the event horizon
I'm trying to understand intuitively the geometry as it would look to an observer entering the event horizon of a schwarszchild black hole. I would appreciate any insights or corrections to the above.
...
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2answers
97 views
What is gravitational speed for a black hole? [duplicate]
Possible Duplicate:
What is the escape velocity of a Black Hole?
This is gravitational speed for earth: $$v=\sqrt {g_{e}r}.$$
What is gravitational speed for a black hole? I want an ...
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341 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 ...
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635 views
Black holes and positive/negative-energy particles
I was reading Brian Greene's "Hidden Reality" and came to the part about Hawking Radiation. Quantum jitters that occur near the event horizon of a black hole, which create both positive-energy ...
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8answers
903 views
Black hole - white hole (collision)
This is it:
Nonspinnig, equally massive black hole and white hole experience a direct collision.
What shall happen? What shall be the result of such a collision?
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1answer
127 views
Do wormhole exits require matter? If not, would they change the edge of the universe?
As a layperson who watches way too many theoretical physics and astronomy documentaries, I've seen the folded-piece-of-paper analogy of wormholes a bajillion times. Usually they explain that black ...
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173 views
Will acceleration rate of expansion of space become faster than speed of light?
From watching cosmology lectures, it seems that the space between galaxies is expanding at an accelerating rate, my question is since it is the space that is (acceleratingly expanding), the special ...
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1answer
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The role of dark matter in black holes and star formation
In my understanding, there exists a critical mass for which a star needs to be in order for it to collapse into a black hole. This also applies to a certain critical density of gas in order for stars ...
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Direct observations of a black hole?
I'm not very knowledgeable about physics generally, but know that nothing can escape a black hole's gravitational pull, not even light (making them nearly invisible?).
My question is: What has been ...
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1answer
216 views
The Strength Of A Black Hole
Does the gravitational strength of a black hole at its singularity change the more it pulls things into it?
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1answer
142 views
Can a charged black hole interact via electromagnetism? [duplicate]
Possible Duplicate:
Detection of the Electric Charge of a Black Hole
Light cannot escape from a black hole. However light is also interpreted as the carrier of the electromagnetic force. So ...
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3answers
309 views
Can every particle be regarded as being a combination of Black holes and White holes?
Can the statement be regarded as true? That every particle, or element in the universe can be regarded as a combination of black hole and white hole in variable proportion.
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1answer
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When would the proposed black hole at the centre of Milky Way gulp in our solar system?
I've heard and read that our solar system lies near to the peripheral region of the Galaxy. Then accordingly we would have a greater probability of sustaining to eventual gulping down by the ...
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1answer
222 views
Wasn't the Hawking Paradox solved by Einstein?
I just watched a BBC Horizon episode where they talked about the Hawking Paradox. They mentioned a controversy about information being lost but I couldn't get my head around this.
Black hole ...
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2answers
542 views
About Susskind's claim “information is indestructible”
I really can't understand what Leonard Susskind means when he says that information is indestructible.
Is that information really recoverable?
He himself said that entropy is hidden information. ...
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3answers
148 views
When a high speed neutrino just misses an old neutron star, why isn't it trapped?
Suppose a neutrino is seen travelling so fast that its Lorentz gamma factor is 100,000. It races past an old, no longer active neutron star, narrowly missing it. As far as the neutrino is concerned, ...
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1answer
182 views
Event horizons without singularities
Someone answered this question by saying that black hole entropy conditions and no-hair theorems are asymptotic in nature -- the equations give an ideal solution which is approached quickly but never ...
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963 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 ...
