All Questions
Tagged with spacetime event-horizon
107
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Can part of space be causally disconnected from the rest of the universe by being surrounded by black holes? [duplicate]
Is it possible for black hole event horizons to overlap and form a spherical wall around an island of space (that's not inside a black hole) while still being causally disconnected from the rest of ...
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How to Understand Negative Energy in the Ergoregion?
I am trying to understand the Penrose process and having trouble explaining negative energy in the ergoregion.
How I interpret it is:
Energy is the dot product between the four momentum of the object ...
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Time required to reach Black Hole's Event Horizon from outsider perspective?
Let's imagine a pair of particles that is entangled. One (call it $P_1$) is released and then falls to a black hole from a distant $x_0$, (for example $x_0=5r_s$) and velocity $v_0(=1/2c)$, while the ...
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Types of singularities
I am confused about the types of singularities. According to my limited knowledge there are two types of singularity. One is space like singularity ( a curvature singularity enclosed within a null ...
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How many null directions are there?
The metric signature of spacetime is usually given as ($3,1$), but spaces can also be ($3,n,1$). Null surfaces include photons and event horizons, which exist, so is $n$ actually $ > 1$ in the ...
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Event horizon in stationary spacetime
In the case of non-stationary spacetimes finding the event horizon is no easy task.
The stationary case should somehow be less involved or so it is in some well known cases, such as the Kerr spacetime....
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2
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2
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If I were to drop my phone into a black hole, would I be able to catch it?
Say, for the sake of argument, I am outside the event horizon of a black hole and accidentally drop my phone (or some other object) into the hole. If I were to enter the black hole, would I ever be ...
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Are black holes 4-dimensional balls of spacetime? If so, will they have 3-sphere surfaces?
If black holes are 4-dimensional balls of spacetime, they will have a 3-sphere surface with a 3-dimensional volume. Would this allow infalling matter to remain within this surface?
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Why isn't there an event horizon in the negative mass Schwarzschild metric?
The negative mass Schwarzschild metric has no event horizon.
Why isnt there a particular radius in which spactime flows outwards at the speed of light? This would imply a region of the solution for ...
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Penrose diagrams and Holographic Principle
What would the Penrose Diagram look like that represented a black hole (call it Black Hole-B), inside of a massive black hole (Black Hole-A), in our universe?
and, as inside of the Penrose diagram for ...
- 190
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Why do we defer to GR when describing black holes rather than rely on QM?
This is a broad question but it's well documented that GR and QM are very well tested in their own domains but they conflict around black holes.
Picture a neutron star slowly accreting matter until it'...
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If it's a common myth that a black hole contains a singularity, what does a black hole actually (likely) contain?
It's a common myth (especially in popsci) that a black hole contains a singularity. However, I cannot find an explanation for what we think a black hole actually does contain. The best I've seen is &...
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Are black holes the edge of our universe?
Are black holes the actual edge of the universe? Because spacetime is another dimension, I would assume the universe doesn’t have perceived corners or edges. At least humans cannot perceive it.
The ...
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429
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Where does the parallel universe in the Penrose diagram come from?
In this diagram, as well as our universe, you have a parallel universe.
Where does this come from? Is this just a artifact of the diagram, or is it predicted by the maths in some sort.
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How exactly does Hawking radiation occur? [duplicate]
I understand some parts of the theory, I've read from here https://phys.libretexts.org/Bookshelves/Astronomy__Cosmology/Supplemental_Modules_(Astronomy_and_Cosmology)/Cosmology/Carlip/...
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