An event horizon is a type of boundary such that any information past this boundary is inaccessible to the observer it is defined for. Common examples are the Schwarzschild radius of a black hole (which is defined commonly for all observers outside this radius) and the cosmological even horizon ...

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Can we build a synthetic event horizon?

If we imagine ourselves to be a civilization capable of manipulating very heavy masses in arbitrary spatial and momentum configurations (because we have access to large amounts of motive force, for ...
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2 Event Horizons come into contact [duplicate]

Just a question out of curiosity, what would happen if the event horizons of 2 black holes of the same mass were to come into contact? Would both gravitational accelerations be canceled where the ...
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Do black holes exist? [duplicate]

Do black holes exist from our point of reference? From our point of reference nothing actually goes inside the event horizon right? So is there anything inside the event horizon from our reference? If ...
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Physical meaning of the Rindler hyperbola vertex and the Rindler lines

Two questions regarding the Rindler diagram: 1) Does the vertex of a given hyperbola in the diagram have physical meaning? I know it is the inverse of the constant proper acceleration ($\alpha$) ...
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Black hole entangled with the cosmological horizon

Maldacena and Susskind recently proposed a interesting and very suggestive duality between entanglement and topological identification: http://arxiv.org/abs/1306.0533 But are such ideas applicable to ...
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Graviton through the horizon and force felt outside a black hole [duplicate]

Gravitational force is mediated by graviton exchange. If I am standing outside a black hole, I can of course feel the attracting force towards the black hole. This should correspond to gravitons ...
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Can a black hole actually grow, from the point of view of a distant observer? [duplicate]

Possible Duplicate: Black hole formation as seen by a distant observer I've read in several places that from the PoV of a distant observer it will take an infinite amount of time for new ...
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Second law of thermodynamics implies a linear cosmology?

If one applies the second law of thermodynamics to the Universe[1] as a whole then one might expect that the entropy of the Universe always increases as time goes forward (or more accurately that the ...
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Is the acceleration at the event horizon of a black hole independent of the magnitude of its radius?

Is the acceleration of a free-falling observer at the Schwarzschild radius of a black hole the same regardless of the numerical value of the radius (i.e. outside of a black hole, is the acceleration ...
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Size of black hole

I am wondering about size of black hole. How is it possible that we have black holes of different sizes? As I know the singularity is point which is infinite small and is infinite dense. So my ...
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Can you enter a timelike hypersurface?

As I understand it, a timelike hypersurface is one that has only spacelike normal vectors. But does this not imply that a the geodesic of a particle crossing it must be spacelike at that point? But ...
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Can Event Horizon be created without actively involving Gravity (Spacetime curvature)?

The definition of Event Horizon I took from Wikipedia: An Event Horizon is a boundary in spacetime beyond which events cannot affect an outside observer. From the definition, I can abstractly ...
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Causal reconnection

Can causally disconnected regions join up again? For example the universe is expanding faster than light creating cosmological horizon, but what if something causes the expansion to slow down and ...
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Black Holes: How does a three dimensional object collapse into a singularity & Where does the matter go?

A black hole comes into existence as the result of the core collapse of enormous stars, which lose quite some mass in a supernova explosion. However, supermassive black holes are still by any means ...
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How can black holes be point-like but have a size?

Presumably all singularities are the same size: a point. What makes one black hole bigger than another? Also, a singularity will only have the same mass (or less) than the collapsed star, so what ...
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If NASA could send a camera into a black hole, could we then see what's inside the black hole?

Inspired by Stephen Hawking I recently tripped upon an idea of what is really inside a black hole. I thought if NASA (or any other space agency) could send a super protected camera into a black hole, ...
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Boundaries of Black Hole and Observable Universe

Are the boundaries of a black hole, the event horizon, similar to the boundary at the end of our observable universe?
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Are the cosmic horizons observer-specific?

It is known that all observers will agree on the position of the black hole event horizon. But what about the cosmic horizon of the de Sitter space? Can one say that the horizon of scientist1 is ...
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Photons hitting the Black Hole Singularity

I was watching one of Dr. Susskind's Lectures on String theory and he was talking about black hole singularities (see the 40 minute mark of this lecture ...
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Is it possible to assign a physical radius to a black hole?

The Schwarzschild metric is given by: $$c^2d\tau^2 = \left(1-\frac{r_s}{r}\right)c^2 dt^2-\left(1-\frac{r_s}{r}\right)^{-1}dr^2 - r^2 \left(d\theta^2 + \sin^2 \theta \, d\varphi^2\right).$$ The ...
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Does light slow down (for an external observer) as it approaches the event horizon?

As I understand, for an external observer nothing even enters a black hole because it takes infinite time in his frame of reference for something to actually reach the event horizon. I also read that ...
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Is the gravitational acceleration at the event horizon constant?

If the escape velocity at the event horizon of a black hole is equal to the speed of light, does this imply that the gravitational acceleration at the event horizon is also constant? For example, ...
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Blackholes gravity, why it has effect outside the event horizon? [duplicate]

If gravity is a curvature of space time, and the event horizon is the collapse of this curvature on itself, then if the blackhole gets more matter after it is formed we should see no effect at all ...
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Is the black hole surface area actually zero?

From quantum mechanics we know that entropy of a part can be smaller than the entropy of the whole. I wonder whether a similar rule works for GR as well. Quantum mechanics predicts that the entropy ...
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How much extra distance to a CERN event horizon? [duplicate]

How much extra distance would a scientist have to travel to get to the event horizon of a mini black hole if they ever make one?
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Something about things going in black hole?

Don't hit me if the question is too lame but here it goes 1) We all know that to see something light must get reflected from it's surface and then reach our eye's 2) Any thing which goes in black ...
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Can the Escape Velocity of Regions inside the Event Horizon of a BH be calculated through Newtonian Physics?

Do Newtonian Physics help in determining the escape velocity at and inside the event horizon at a distance less than Schwarzchild Radius from the singularity?
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Fine structure parameter $\alpha$ at event horizon

As magnetic field lines collect at a black hole event horizont (for no field lines will be present in the black hole) then ratio of electric field to magnetic field will change, so by this change in ...
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Way to escape from a black hole

I’ve had a question on WHY a traveler couldn’t “escape” from a black hole under specific conditions (I have an image I'd like to send to clarify, but the website won't let me)> The key is for the ...