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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22 views
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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0answers
51 views
Entanglement and Black holes
If you have two entangled quantum states, One state falls into a black hole and you measure the other state, What can you say about the state that has fallen into the black hole?
If you have billions ...
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0answers
51 views
Gravitational redshift of Hawking radiation
How can Hawking radiation with a finite (greather than zero) temperature come from the event horizon of a black hole? A redshifted thermal radiation still has Planck spectrum but with the lower ...
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1answer
81 views
Is it possible (theoretically) to divide Black Hole into two parts? [duplicate]
I have read that it's not possible.
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1answer
36 views
What's the criteria for black hole thermodynamically stability? (And dynamical?)
It looks like usual criteria (positivity of Hessian; what geometrically means a cancave of entropy) is no useful, becouse entropy is not additive and not extensive for black hole. Then what is the ...
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0answers
39 views
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 ...
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0answers
27 views
Dark Energy, Space Time and Black Holes [closed]
Since space and time are both one and the same would that mean that as time passes and accumulates after the big bang that space is forced to grow? This would explain why all the galaxies are speeding ...
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2answers
41 views
Do black holes have charges?
Do black holes have charges? If so, how would they be measured? Also, does electricity behave the same way? Black holes affect photons, which are carriers of EM radiation, so do black holes have any ...
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5answers
277 views
Theoretical physics and education: Does it really matter a great deal about what happens inside a black hole, or about Hawking radiation? [closed]
I stumbled across this article http://blogs.scientificamerican.com/cross-check/2010/12/21/science-faction-is-theoretical-physics-becoming-softer-than-anthropology/
It got me thinking. Why do we ...
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30 views
How connected thermodynamical stability and dynamical stability for black holes?
Criteria for thermodynamical stability is the convex of entropy. But for black hole entropy is non-additive.
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1answer
75 views
Will the black hole evaporate in finite time from external observer's perspective?
There is the problem that is bothering me with the black hole evaporation because of Hawking radiation.
According to Hawking theory the black hole will evaporate in finite time because of quantum ...
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0answers
15 views
Pair production intefering with gamma-ray laser black hole fabrication
A common "proposal" to make a micro black hole is to use on the order of 10^12 kg of gamma-ray lasing medium and focus all the light at a small point. However, intense light will interact with itself ...
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1answer
48 views
Why does the Kruskal diagram extend to all 4 quadrants?
Why is it that the Kruskal diagram is always seen extended to all 4 quadrants when the definitions of the $U,V$ coordinates don't seem to suggest that the coordinates are not defined in, say, the 3rd ...
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2answers
88 views
Why don't black holes within a galaxy pull in the stars of the galaxy
visit http://www.nasa.gov/audience/forstudents/k-4/stories/what-is-a-black-hole-k4.html
If black holes can pull even light, why cant they pull the stars in the galaxy?
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0answers
69 views
Is there any proof that the speed of gravity is limited? [duplicate]
I must warn that though I'm argumenting with black holes I'm not asking how does gravity escape the black hole!. I want to know if the absolute speed of gravity waves were proven bu an experiment.
We ...
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3answers
105 views
Is it possible to have a singularity with zero mass?
A singularity, by the definition I know, is a point in space with infinite of a property such as density.
Density is Mass/Volume.
Since the volume of a singularity is 0, then the density will thus ...
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2answers
94 views
Is time going backwards beyond the event horizon of a black hole?
For an outside observer the time seems to stop at the event horizon. My intuition suggests, that if it stops there, then it must go backwards inside.
Is this the case?
This question is a followup ...
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2answers
104 views
What is a sudden singularity?
I've seen references to some sort of black hole (or something) referred to as a sudden singularity, but I haven't seen a short clear definition of what this is for the layman.
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2answers
88 views
How can we detect a black hole? [duplicate]
If black holes are phenomena of very high density (gravitational singularities) which don't emit radiation how can we detect them so far away from us where so much other radiation can hide the black ...
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3answers
54 views
Spaceship split near event horizon
Lets say there's two astronauts, Alice and Bob, going on a space trip to a super-massive black hole. So large that they wouldn't notice any significant spaghettification forces at the event horizon. ...
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1answer
42 views
“WLOG” re Schwarzschild geodesics
Why, when studying geodesics in the Schwarzschild metric, one can WLOG set
$$\theta=\frac{\pi}{2}$$
to be equatorial? I assume it is so because when digging around the internet, most references seem ...
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1answer
47 views
Would the universe get consumed by blackholes because of entropy?
Since the total entropy of the universe is increasing because of spontaneous processes, black holes form because of entropy (correct me if I'm wrong), and the universe is always expanding, would the ...
2
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1answer
55 views
Relativistic Computation?
Is it possible to employ relativity to develop computational technology?
Here is a really basic example:
Build a Computer and Feed it the Problem (say the problem is projected to take 10 years to ...
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0answers
49 views
Singularities in Schwarzchild space-time
Can anyone explain when a co-ordinate and geometric singularity arise in Schwarzschild space-time with the element
$$ ...
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2answers
90 views
What happens to things when things get crushed in a blackhole [duplicate]
When a black hole destroys things until they are smaller than molecules, where does it go and what happens when it clogs up?
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1answer
79 views
Why does the Schwarzschild radius become excessively large after a certain point?
Here's something that I've found difficult to wrap my head around. The relationship between the Schwarzschild radius and mass is linear. It's generally known that if you take an object in the universe ...
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1answer
50 views
Does non-mass-energy generate a gravitational field?
At a very basic level I know that gravity isn't generated by mass but rather the stress-energy tensor and when I wave my hands a lot it seems like that implies that energy in $E^2 = (pc)^2 + (mc^2)^2$ ...
9
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1answer
105 views
General definition of an event horizon?
Horizons are in general observer-dependent. For example, in Minkowski space, an observer who experiences constant proper acceleration has a horizon.
Black hole horizons are usually defined as ...
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1answer
53 views
What is mathematical definition of a strong gravity?
Mathematical definition of a weak gravity is simple $g=\frac{GM}{r^2}$
but what is mathematical definition of a strong gravity? (blackhole-like or close to a blackhole-like object)
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3answers
124 views
Why are black holes special?
A black hole is where it's mass is great enough that light can't escape at a radius above the surface of the mass?
I've been told that strange things happen inside the event horizon such as ...
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2answers
163 views
Is a black hole a perfect black body?
A black body absorbs all light/radiation in its reach. According to basic laws of physics, the more energy a body absorbs the more it can emit. Therefore, a black body absorbs all energy directed at ...
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3answers
113 views
What would happen to the Moon if Earth is turned into a black hole?
Assume that all of sudden the Earth is turned into a black hole. And the moon revolves around the Earth (before turning into a black hole). What would happen to the Moon after earth changes to black ...
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1answer
59 views
How small the earth should be for it to become a black hole
How small would the earth have to be squashed so that it would become a black hole?
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1answer
307 views
Overcharging a black hole
Hubeny's 1998 paper got a lot of people interested in determining whether cosmic censorship can be violated by dropping too much charge onto a black hole. It suggested that you might be able to get a ...
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Magnetic field-pulsed microwave transmission line
Here's the reference:
The researchers showed that a magnetic field-pulsed microwave transmission line containing an array of superconducting quantum interference devices, or SQUIDs, not only ...
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4answers
203 views
Time inside a Black hole
If time stops inside a black hole, due to gravitational time dilation, how can it's life end after a very long time? If time doesn't pass inside a black hole, then an event to occur inside a black ...
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1answer
66 views
The paradoxical nature of Hawking radiation [duplicate]
The definition of a classical black hole is when even electromagnetic radiation can not escape from it. Why then can Hawking radiation be emitted from semi-classical black holes?
What is difference ...
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4answers
876 views
Why do we care about black hole interiors' physics?
Whatever happens in there is not falsifiable nor provable to the outside. If for (amusing) example the interior consisted of 10^100 Beatles clones playing "Number Nine" backwards, do we know how to ...
6
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1answer
40 views
What is baryon loading in the context of gamma ray bursts (GRBs)?
I've read that with short hard gamma ray bursts (shGRBs) associated with the coalescence of NS-NS and NS-BH binaries are expected to be beamed along the axis of the orbital angular momentum (i.e. ...
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6answers
133 views
Is black hole bright at center?
As we know that light photon cannot escape the gravity of black hole so I was thinking that if that is the surface of the black hole would be bright as all the photons would be there only. Am I right ...
5
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0answers
78 views
Do semiclassical GR and charge quantisation imply magnetic monopoles?
Assuming charge quantisation and semiclassical gravity, would the absence of magnetically charged black holes lead to a violation of locality, or some other inconsistency? If so, how?
(I am not ...
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157 views
Spacetime around a Black Hole
If we consider the sun, then space-time is curve around it. My question is that what is the kind of curvature of space and time around the black hole. Is that space and time more curved around the ...
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1answer
52 views
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 ...
2
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1answer
86 views
Diving into a charged (Reissner-Nordstrom) Black hole
Apparently there are two event horizons in this type of black hole, where the second one is known as the Cauchy horizon. According to Carroll, if you go into the first one, you will fall until you ...
2
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1answer
94 views
Reconstruction of the initial state from Hawking radiation?
I hear that unitary evolution and information conservation must imply that information about information content that defines the initial state of matter used to create a black hole can be inferred ...
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3answers
233 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.
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2answers
106 views
Future light cones inside black hole
In Caroll's Spacetime and Geometry, page 227, he says that from the Schwarzschild metric, you can see than from inside a black hole future events all lead to the singularity. He says you can see this ...
5
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2answers
116 views
Do neutrinos of any flavor get trapped in black holes?
This question has been bothering me a bit. I know that neutrinos have super small mass and they interact via the weak force. Since they have a non-zero mass, they should be affected by black holes and ...
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0answers
66 views
Are quarks the limits? The end of the fundamental science. For collisions on more higher energies will lead to black holes after all?
Are quarks the limit and the Plank scale is believed to be the limit of distance when the very concept of space and length cease to exist (10^-19)
Any attempt to research the existence of shorter ...
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Can negative energy explain blackholes?
I think black holes are peculiar and I want to know if there is a relation to negative energy. Does negative energy have positive mass and therefore can explain the nature of black holes? IS there any ...
