All Questions
Tagged with spacetime general-relativity
298
questions with no upvoted or accepted answers
11
votes
1
answer
458
views
Aren't black holes required to exist forever in our frame of reference instead of evaporating?
I know that for an observer far away, nothing ever crosses a black hole horizon (due to time dilation), while in the frame of reference of a falling observer the horizon is nothing special on its way ...
- 3,771
7
votes
1
answer
298
views
Charged versus rotating black holes as different kinds of wormholes
I've heard that a maximally extended charged black hole can be a traversable wormhole to the same universe whereas a maximally extended uncharged rotating black hole can only be a wormhole to ...
- 25.7k
6
votes
0
answers
262
views
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
5
votes
0
answers
128
views
Is it possible to create a Nil geometry in real spacetime according to general relativity? (What metrics are possible in the real world?)
Background
I've heard that it is possible to construct a Penrose triangle in the 3D geometry Nil. And I wondered: Can we build a Penrose triangle in the real world if spacetime is appropriately ...
5
votes
0
answers
260
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Help understanding the Cartan connection/formalism in General Relativity
I'm trying to understand the Cartan formalism in the context of General Relativity.
As I understand it given a pseudo-Riemannian spacetime manifold $M$ we can consider the group of spactime ...
- 2,847
5
votes
0
answers
761
views
On the embedding of the Schwarzschild metric in six dimensions
At every point of the 4-D space-time, it's metric, being a symmetric 2-tensor, has $\frac{D(D+1)}{2}=10$ independent components. From this we can subtract four degrees of freedom according to the four ...
- 1,349
5
votes
0
answers
782
views
Does any spacetime admit a global foliation in spacelike hypersurfaces?
In the comments of this question the following new questions came up: in general relativity, local coordinates can be found around any point, that single out a time coordinate and a three dimensional ...
- 9,304
4
votes
0
answers
92
views
Is the causal structure completely determined by the Weyl tensor alone?
By causal/conformal structure I mean the context of Malament's 1977 theorem. If I understand correctly this means that any two spacetimes which agree about all of the future-directed continuous ...
- 151
4
votes
1
answer
112
views
How to relate Riemannian and Lorentzian tetrad fields on the same manifold/spacetime?
Consider Gibbons and Hawkings paper wherein a Riemannian metric $\overset{\mathcal{R}}{g}_{\mu\nu}$ and everywhere well defined normalized line field $l_{\mu}$ on spacetime $M$ may be used to ...
- 2,847
4
votes
1
answer
122
views
Spacetime metrics extended to negative radius
In the Kerr metric
$$
ds^2=\left(1-\frac{2Mr}{\rho^2}\right)dt^2+\frac{4Mar\sin^2\theta}{\rho^2}dtd\varphi-\frac{\rho^2}{\Delta}dr^2-\rho^2d\theta^2-\left(r^2+a^2+\frac{2Ma^2r\sin^2\theta}{\rho^2}\...
- 123
4
votes
0
answers
84
views
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
4
votes
0
answers
125
views
How is it possible that a closed null geodesic be incomplete?
In page 190 of "The Large Scale Structure of Spacetime" (Hawking & Ellis), it says:
...there must be a closed null geodesic curve $\gamma$ through $q$. Let $v$ be an affine parameter on ...
- 41
4
votes
0
answers
72
views
Is there an equivalent of Kaluza-Klein for fermionic dimensions?
Taking GR in $D$ dimensions, one can use the process of compactification to turn this into GR in $D-1$ dimensions coupled to a Yang-Mills field. i.e. you start with spin-2 fields and you and up with ...
user84158
4
votes
0
answers
241
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A question regarding Leonard Susskind's ER=EPR lecture
https://youtu.be/OBPpRqxY8Uw?t=1315 Right at this instance of the video Susskind starts talking about how space is actually connected by entanglement. (You should watch the video for a accurate ...
user212860
4
votes
0
answers
217
views
Kerr metric in BMS (Bondi-Metzner-Sachs) coordinates
I am trying to put the Kerr metric into the famous Bondi gauge, which is given for instance by the formula (6.2.10) at page 154 of the following paper: https://arxiv.org/abs/1801.01714. Now, Barnich ...
- 96