All Questions
Tagged with black-holes causality
107
questions
2
votes
2
answers
136
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What happens if $ a^2 > M^2 $ in Kerr metric?
(Boyer-Lindquist coordinates and $ c = G =1 $ taken)
As I know, line element in Kerr metric $ d s^2 = - \left( 1 - \frac{2Mr}{\rho^2} \right) d t^2 - \frac{4 M a r \sin^2 \theta}{\rho^2} d \phi d t + \...
- 126
0
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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 ...
- 207k
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 ...
- 1
8
votes
6
answers
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Gravity on supermassive black hole's event-horizon
$M =$ black hole mass
Gravitation is about $r^{-2}$
Schwarzschild radius, $r_{\text{S}}$, is $\propto M$
So, more massive black holes have weaker gravitation at their event horizon.
Consider a black ...
- 740
4
votes
0
answers
60
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Can wormhole inside a black hole become an escape?
I did not major in Physics so not sure if this is a proper question; but according to some Google search there do exist papers discussing wormhole inside black hole like this, which I am not able to ...
- 141
21
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5
answers
3k
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Does an object approaching a black hole ever cross the combined event horizon of the black hole and itself?
Once you start studying black holes, one of the first things you'll probably hear is that from an outsider's perspective objects falling into the black hole take an infinite time to do so due to time ...
- 12.4k
1
vote
1
answer
111
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Carter-Robinson Theorem
There are uniqueness theorems that classify Black holes according to its mass, angular momentum and charge. One of the theorem is Carter-Robinson theorem which has many assumptions and then it says ...
- 207k
13
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4
answers
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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 ...
- 207k
1
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0
answers
83
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What is the meaning to the switch $dt^2\to-dt^2$ and $dr^2\to-dr^2$ in the Schwarzschild metric?
What is the meaning of the change $dt^2\to-dt^2$ and $dr^2\to-dr^2$ in the Schwarzschild metric, leading to:
$$g=-c^{2}d\tau^{2}=(1-\frac{2GM}{c^{2}r})c^{2}dt^{2}-(1-\frac{2GM}{c^{2}r})^{-1}dr^{2}+r^{...
- 207k
4
votes
3
answers
319
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When can information escape from a black hole through a warp bubble-like spacetime?
It is well known that nothing can escape a black hole, including gravitational radiation. Many questions have been asked here about this topic, such as:
Can gravitational waves escape a black hole?
...
1
vote
2
answers
288
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Can you fall into a black hole, and then back out again?
There is a innumerable number of questions on this site about black hole event horizons, the possibility of falling in and back out again, but none of them answer my question specifically.
I have read ...
2
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2
answers
161
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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 ...
- 1,290
1
vote
1
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168
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Does a geodesic exist that will take someone across the event horizon?
I saw the movie "Interstellar" a few years back, and was amazed that Cooper was able to fall from 1 AU into a black hole before his daughter turned 110. Intuitively, I would think that there ...
- 103k
0
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2
answers
113
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Light-like vector in Schwarzschild metric
If I shoot a light ray radially, assuming the Schwarzschild metric, what vector would I plug in to the metric tensor to get a relationship between the $t$ and $r$ coordinates? That is what vector do I ...
- 133k
2
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2
answers
168
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Can a body escape a black hole by being thrusted? [duplicate]
I am told many time that nothing can escape black-hole because black-holes escape velocity is more than speed of light. But we know object don't necessarily have to exceed speed of light to escape a ...
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