All Questions
60
questions
0
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1
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76
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Black Hole Formation -- How Can an Event Horizon be Observed to Grow? [duplicate]
This is a question about black hole formation. To be clear, I’m not suggesting that black holes don’t form. It’s that I’m having trouble with the accepted explanation so there’s a flaw in my logic ...
- 21
2
votes
0
answers
40
views
Calculating Gaussian Curvature for metric
I am trying to calculate Gaussian curvature of an optical metric
$$
d \sigma^2=\frac{r\left(\omega_{\infty}^2-\omega_e^2\right)+2 m \omega_e^2}{(r-2 m) \omega_{\infty}^2}\left(\frac{d r^2}{1-\frac{2 m}...
- 21
0
votes
3
answers
99
views
Does the Schwarszchild solution require the cosmological constant to stop it from expanding?
When Einstein developed his field equations for general relativity, he attempted to apply them to the entire universe. He found the universe had to expand, which at the time was believed not to be the ...
- 131
1
vote
2
answers
78
views
Probability of a primordial black hole absorbing background radiation?
I'm thinking of the early universe when there was a lot of energetic radiation around. A primordial black hole (PBH) that would be about to evaporate completely about now, would have an initial mass ...
- 6,112
0
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45
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What is the difference between the cosmological and the black hole horizons in thermodynamics?
I want to know the different thermal behaviors between cosmological and black hole horizons, such as temperature, entropy and so on.
- 113
2
votes
0
answers
61
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Gravitational deflection of light and the second Friedmann equation
Is the fact that light bends twice as much as matter does in Schwarzschildian gravitational fields related to the implication of the second Friedmann equation (in which $\ddot{a}\propto\rho + 3p$, ...
- 41
1
vote
0
answers
22
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Big Crunchs and Event horizons [duplicate]
There are Two different defintions for the event horizon of a black hole.
The Absolute horizon and the Apparent horizon.
An apparent horizon is a surface that is the boundary between light rays that ...
- 2,908
0
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0
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73
views
Does spacetime move? With respect to what?
Can spacetime itself rotate along a body, like a black hole? Would it move like a wave?
- 495
1
vote
2
answers
245
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How is the interior Schwarzschild metric derived?
Where does the interior Schwarzschild metric come from? How is it derived and why does it have NOT a singularity? Would it mean that the singularity is only apparent and for those out of the black ...
- 495
2
votes
1
answer
115
views
Maximum density of a black hole
From Schwarzschild metric, we know that every concentration of matter and energy such that all of its mass $M$ is concentrated in a radius $r_s\leq\dfrac{2GM}{c^2}$ turns into a black hole.
...
- 495
0
votes
1
answer
353
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Has this random youtube crackpot trying to disprove GR inadvertedly stumbled on a genuine prediction of it? [duplicate]
I'm an Astrophysics major. I was watching strange fringe physics crackpots on Youtube to make fun of them, because I'm an acollierastro, planarwalk kinda gal. I came across this guy who thinks Black ...
2
votes
3
answers
383
views
Is there any remote possibility that a singularity may be real? [closed]
Usually, when physicists talk about singularities in Einstein's theory of relativity, they say that these cannot exist and that they are only mathematical artifacts that indicate that is likey that ...
- 2,462
1
vote
0
answers
23
views
In the Steinhardt's bouncing cosmology, how would the CMB differ for patches close to pre-existing black holes
In Steinhardt's bouncing cosmology model, during the contraction phase the Hubble radius shrinks to microscopic sizes, although the overall contraction of the universe is much less significant. Each ...
- 11
9
votes
2
answers
467
views
What does it mean that "relativistic material becomes cosmologically coupled to the expansion rate" in the recent dark-energy black-hole paper?
The recent paper "Observational Evidence for Cosmological Coupling of Black Holes and its Implications for an Astrophysical Source of Dark Energy" has made a splash in the popular press. ...
- 48.4k
8
votes
1
answer
632
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We say the big bang (initial singularity) didn't happen at a point, but is it the same with the singularity of a black hole?
I have read this question:
The simple answer is that no, the Big Bang did not happen at a point. Instead, it happened everywhere in the universe at the same time. Consequences of this include
The ...
- 29k