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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Black holes have conservative potentials. Why don't things “swing” in and out?

Black holes attract objects via gravity, which is a conservative force. Thinking from conservation of energy, It seems like for an object moving toward them, they should be able to "swing" into and ...
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Black hole no-hair theorems vs. entropy and surface area

I was revisiting some old popular science books a while ago and two statements struck me as incompatible. No-hair theorems: a black hole is fully-described by just a few numbers (mass, spin etc) ...
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Does black hole formation contradict the Pauli exclusion principle?

A star's collapse can be halted by the degeneracy pressure of electrons or neutrons due to the Pauli exclusion principle. In extreme relativistic conditions, a star will continue to collapse ...
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Light Sheets and the Holographic Entropy Bound

I'm trying to understand light sheets as related to the holographic entropy bound for information. This bound equates the information on a surface (e.g. the event horizon of a black hole) with the ...
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51 views

Motion without matter

Suppose you have a vacuum spacetime with non zero cosmological constant then you can show that two test particles will move toward each other or apart depending on whether it is negative or positive ...
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222 views

Whether the holographic universe of string theory prove the hypothesis of the holographic universe created by David Bohm or not?

Bohm, David (1980), Wholeness and the Implicate Order, London: Routledge, ISBN 0-7100-0971-2 As we can see from the book above, David created the hypothesis of the holopraphic universe in 1980. And ...
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Near horizon limit of near-extreamal black brane

It is known that the near horizon limit of a ($d+1$) dimensional extremal charged black hole (BH) is $AdS_2\times S^{d-1}$. I was looking at this paper by Faulkner et al. They consider a ($d+1$) ...
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What are White Holes?

What are white holes? How do they affect spacetime? A black hole has extreme gravity which bends the spacetime fabric, but what does a white hole do? Also, what are they made of?
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“Center of a black hole is a time”

$\newcommand{\d}[1]{\mathrm{d} #1}$In one lecture (around 1:33:15) of the series of lectures "Theoretical Minimum" of Prof. Susskind he talks about black holes and the Schwarzschild metric: $$\d ...
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Killing vectors in General Relativity?

I'm looking to derive the surface area of the event horizon of a Schwarzschild black hole. I was just wondering if it were possible for someone to explain to me this: $$ ...
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Observer inside event horizon of an extremely large black hole [duplicate]

Imagine a very large black hole, with a mass equal to a large number of galaxies. Assume a space station is in orbit around the black hole some distance from the event horizon at a point A. An ...
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Gravitational Time Dilation and Schwarzschild Coordinates

So I'm trying to use this equation for the time dilation of an object, but I don't know how to get the distance that I have (in meters) to a radial coordinate in terms of schwarzschild coordinates. ...
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Evidence of possible tidal effects close to a gravitational wave emitting system

Currently we are attempting to detect gravitational wave emissions using the LIGO gravitational wave detection system (and similiar systems), by attempting to detect very weak gravitational waves ...
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Why does Hawking radiation cause black holes to die? [duplicate]

If a particle is being expelled from a black hole and an antiparticle is being driven into it, shouldn't the opposite occur as well and in the same frequencies? I mean, black holes should emit ...
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1answer
376 views

What happens to the total volume of a chunk of space that is being sucked into a black hole?

Does it increased, decrease, or stay the same? Maybe it explodes to infinity... Here is a similar question: Do black holes have infinite areas and volumes? But it's different because it asks how to ...
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Topology of Anti-de Sitter manifold with black hole

I'm interested in understanding the topology of space-time with a black hole. In other words how does having a black hole affect quantities such as the fundamental group, de-Rham cohomologies, Euler ...
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How do shock waves form in space?

Today my aerodynamics professor mentioned that the equations we were learning for atmospheric shock waves can also be applied by astrophysicists to study black hole-related shock waves in space. How ...
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Coordinate velocity and free-falling past an event horizon

Ws can re-arrange the standard Schwarzschild metric as $$\left(\frac{d\tau}{dt}\right)^2=\frac{r-1}{r}\left[1-\left(\frac{r}{r-1}\frac{dr}{dt}\right)^2\right]$$ Where $\frac{r-1}{r}$ is the local ...
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What is Hawking Hartle vacuum state and why does the following Euclidean path integral gives the wave functional of it?

I am studying the wave function of black hole via the paper by Sergey Solodukhkin, Entanglement entropy of black holes,arXiv:hep-th: 1104.3712. In the paper, equation (53) is as follows: ...
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What are “local degrees of freedom in gravity”, and why do they lead to fixed energy densities?

I am reading Jan de Boer's review of the AdS/CFT correspondence and I quote from end of page 1, where he is talking about equivalence of $(d+1)$-dimensional gravity to $d$-dimensional field theory ...
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Are black holes naked singularities for an observer within the event horizon?

A naked singularity means that you can see an infinitely dense thing. Black holes don't count because it sucks up all the light, so you won't see or otherwise detect it. But wait, if you are within ...
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Can a black hole exist without encircling stars? Can a black hole exist without stellar dispersion of a galaxy bulge?

The M–sigma (or M–σ) relation is an empirical correlation between the stellar velocity dispersion σ of a galaxy bulge and the mass M of the supermassive black hole at its center. ...
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Higher dimensional trapped surface and its condition?

In higher D-dimensional spacetime, a marginally trapped surface is a closed spacelike (D-2)-surface whose outer null normals have zero convergence. It is very like a marginally trapped surface in the ...
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106 views

Why does a black hole grow when it consumes matter? Isn't this a contradiction?

I've been thinking about this for a while but can't get my head around it. A black hole's mass is such that its gravity can overcome light. Its event horizon, as I see it, is the boundary up to which ...
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Further explanation of the Penrose Conjecture

I'm currently a third year maths undergrad, writing a dissertation on the application of minimal surfaces in space. I have recently come across the Penrose Conjecture that the mass of a spacetime is: ...
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Am I experiencing any effect from black holes gravitational pull?

So we know that there is a black hole in the middle of the Milky Way. Am I experiencing any effect from the high gravitational pull of the black hole? If no...then why? If yes...then how much?
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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 ...
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Black hole surrounding an object?

When a particle crosses the event horizon of a black hole, at one short moment in time would it appear for that particle as if it was surrounded by a black hole? Regardless of which direction you ...
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Is there a center of gravity in black hole?

I've come across this particular gif "http://i.imgur.com/AOCqg5j.gifv" If you can see the above gif, you can see the two perfectly spherical black holes merge together forming a single larger ...
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How should I interpret relativistic mass? [duplicate]

If I have a mass that gets accelerated to a near the speed of light, before it gets I would think its relativistic mass would expand its Schwarzschild radius enough to turn it into a black hole. I ...
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72 views

How does the expansion of the Universe affect Black Holes?

As know our Universe is expanding, which I have always visualised as some stretching of the metric of space-time, which "flattens" it. In the same time. our theoretical perception of Black Holes ...
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Would the detection of advanced waves be possible in curved space-time?

In the transactional interpretation of quantum mechanics reference 1, inspired by the Wheeler–Feynman absorber theory, a transaction is formed between the emitter and absorber by a superposition of ...
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Do Events Take Place Inside Black Holes?

As you approach a black hole, the universe you observe slows down. When you see someone from outside approaching a black hole, you see how they freeze in time as they get closer and closer to the ...
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Can a black hole collapse in itself?

As we know that the black hole is a lump of highly dense matter, and that's the reason for it's so strong gravitational force. Bat let us assume that it has sucked up a huge amount of mass and it's ...
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Are electrons just incompletely evaporated black holes?

Imagine a black hole that is fast-approaching its final exponential throws of Hawking evaporation. Presumably, at all points in this end process there there will remain a region that identifiably ...
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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 ...
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Is entropy violated inside black holes and worm holes?

Do the laws of thermodynamics hold true everywhere in universe ? What about black holes and worm holes ?
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Primordial black hole mass [closed]

Use dimensional arguments to combine the fundamental constants $\hbar$, $c$ and $G$ to derive the least massive primordial black hole formed shortly after the big bang. I'm not sure how to combine ...
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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 ...
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Popular books on cutting-edge physics [closed]

I watched this video, in which different types of topics are discussed like Quantum Information, Quantum Computation, Universe as hologram, Hidden information, Quantum Entanglement, Black holes and ...
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Thermal radiation in the Unruh Effect

The following formula has been given in 't Hooft's black holes notes ($|\Omega \rangle$ is the vacuum state of Minkowski space, O is a operator): $$\langle \Omega| O|\Omega \rangle = \sum_{n \ge 0} ...
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Any tips on evaluating Riemann tensor?

I am calculating the Riemann tensor for the Schwarzschild solution. I've calculated all 9 non-vanishing Christoffel symbols already. Now I need to evaluate the Riemann tensor and I find no easy way to ...
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Schwarzschild metric: Change in coordinates corresponds to change in object?

I have been reading about the Schwarzschild metric in the book "General Relativity: An Introduction for Physicists" by Hobson, Efstathiou and Lasenby and it appears to say something counter intuitive. ...
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Do we know for sure that black holes must contain a singularity? [duplicate]

I've perhaps naively wondered for years whether there are any rules or proofs that allow us to know for sure that if all an object's mass is contained within its Schwarzschild radius it must be a ...
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High energy photon collapsing into its own black hole

If I did not mess up the math, a photon with a wave length of $$ \lambda = \sqrt{2\pi}\, l_p$$ where $l_p$ is the Planck length has a mass (energy/$c^2$) of $$ m = \sqrt{2\pi}\, m_p$$ where $m_p$ ...
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Gravitational Lensing by Sagittarius A in the center of the Milky Way

It was suggested that there is a black hole in the center of the Milky Way, called Sagittarius A. The whole region is heavily obscured by dust, although some very long wavelengths can break through. ...
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Would a collision of two black holes emit any electromagnetic radiation?

The video linked in this answer shows how space-time would be distorted during such an event. No doubt such an event would be an extremely strong source of gravitational waves. But would anything be ...
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Neutron stars and black holes

The official limits for a neutron star is $1.4 - 3.2\;M_\odot$. But I read that the limit depends on the particular structure of a star to estimate which mass it must have. I also read that neutron ...
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How does a sonic black hole (or dumb hole) work?

I came across this term and I heard they used sonic black holes to detect something analogous to hawking radiation, but I have failed to find sources which explain how exactly they work and how they ...