All Questions
Tagged with spacetime event-horizon
14
questions with no upvoted or accepted answers
6
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0
answers
262
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Why are there multiple universes in the Reissner-Nordström solution?
I am trying to make sense of the Penrose diagram of a non extremal Reissner-Nordström spacetime, that is, the solution with two horizons. The coordinates are
$$ v'=\text{exp}\left(\frac{r_+-r_-}{2r_+^...
- 873
4
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0
answers
84
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Conformal Diagram for Astrophysical Black Hole
I have a question about the conformal diagram of an ‘astrophysical’ black hole which forms in finite time (but with no evaporation).
Usually I see the conformal diagram presented as something similar ...
- 55
3
votes
1
answer
79
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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 ...
- 63
3
votes
0
answers
359
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Why is surface gravity named this way?
I've come across two definitions of surface gravity.
We look at the killing horizon of a Killing vector field $\xi$ and we find from the definition that $\xi_\nu \nabla^\nu \xi^\mu = \kappa \xi^\mu$....
- 2,849
1
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67
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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 ...
- 21
1
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0
answers
95
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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
1
vote
0
answers
53
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Are objects that fall into a black hole *always* silhoutted against the Hawking radiation coming out?
There are many questions on this site about whether you can really fall into a black hole - some seem to say clearly yes, some say clearly no. So let's try one more stab at this one with a narrower ...
- 309
1
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0
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133
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What would the eternal black hole look like?
The white hole and black hole regions in a Kruskal diagram are said to be actually two different locations. Given the problems with white holes it might be a silly question but, hypothetically, what ...
- 780
0
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81
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End points of event horizon
I am reading The Nature of Space and Time by S. W. Hawking. In the last paragraph on page 16 he said that:
event horizon may have past end points but don't have any future end points
I understand ...
- 59
0
votes
1
answer
116
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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 ...
0
votes
1
answer
125
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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....
- 1,989
0
votes
1
answer
115
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What (if any) significance exists in the analogy between the speed of light limit and the Schwartzchild radius of a black hole
I have always been intrigued by what seems to be very similar characteristic of the phenomena of traveling very, very fast, (close to the speed of light , and the Schwartzchild radius.
AS a body gets ...
- 190
0
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0
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169
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The event horizon of a black hole is a spacetime codimension 1 null surface
The event horizon of a black hole is a spacetime codimension 1 null surface.
Why must the event horizon be a codimension 1 surface?
Why must it be a null surface?
Edit:
For reference, see the ...
- 3,203
-1
votes
2
answers
174
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Can Alcubierre Space Drive function in space time within event horizon of a Black Hole?
Alcubierre Drive compresses space in front and propagates as such but in a singularity where space is untraversable is propagation possible? If so can you prove it?
