All Questions
5
questions
1
vote
1
answer
207
views
Is it enough to give a time-orientation to define a spin structure?
Maybe I got it wrong and my question doesn't make sense, excuse me if that's the case. For a smooth Lorentz 4-manifold $(M, g)$ with signature $(- + + +)$ is it enough to give a time-orientation to ...
- 87
2
votes
1
answer
140
views
Spacetimes with "celestial Riemann surface" other than the sphere
In the standard study of asymptotically flat spacetimes one defines null infinity demanding that topologically ${\cal I}^\pm \simeq \mathbb{R}\times S^2$ (c.f. Definition 1 of this review by Ashtekar)....
- 36.5k
7
votes
3
answers
590
views
Rigorous procedure of gluing together two spacetimes
There seems to exist a procedure of "gluing two spacetimes together". In particular I've seem this mentioned in the context of gravitational collapse.
The examples I've seem were that of gluing ...
- 36.5k
4
votes
1
answer
227
views
Are there any restrictions on building the topology of spacetime out of the complement of open balls?
I assume that for a Lorentzian manifold (i.e. with Minkowski signature), the analog of an open ball is the interior of a light cone. My question is motivated by the observation that whereas any point ...
6
votes
1
answer
403
views
An issue about the compactness and the existence of CTCs
There is a well known fact that a compact spacetime necessarily contains a closed timelike curve (CTC). Proof can be found in several books on GR (e.g. Hawking, Ellis, Proposition 6.4.2), and in ...
- 285