Has anyone read this new paper on extending the BGV?

In summary, the conversation discusses a new paper by Will Kinney and others which presents a new version of the Borde-Guth-Vilenkin theorem. This theorem states that any spacetime with net positive expansion must be geodesically incomplete. The paper uses the fluid flow formalism of General Relativity and makes no assumptions about energy conditions. It is applicable to cosmological models using the standard FLRW metric and related expanding metrics but not to other conformal metrics.
  • #1
Luis Mijares
1
1
TL;DR Summary
I was wondering if someone could explain this paper to me
Space news on Phys.org
  • #2
It only talks about net expanding metrics on a locally de Sitter space in a time interval, so while it would apply to cosmological models using the standard FLRW metric and related expanding metrics like the LTB metric, as well as the metrics used in Penrose's Cyclic Cosmology, it wouldn't apply to any cosmological model which doesn't have a net expanding metric on a locally de Sitter space in a time interval. For example, one class of conformal metrics talked about in Lucas Lombriser's recent paper "Cosmology in Minkowski space" occurs in static Minkowski space and thus is not net expanding or in locally de Sitter space, and wouldn't be affected by the result in the paper.
 
Last edited:
  • Like
Likes Luis Mijares
  • #3
FWIW, BGV is a reference to the Borde-Guth-Vilenkin (BGV) theorem which states that any spacetime with net positive expansion must be geodesically incomplete. The paper and its abstract are as follows:

[Submitted on 20 Jul 2023]

The Borde-Guth-Vilenkin Theorem in extended de Sitter spaces​

William H. Kinney (Univ. at Buffalo, SUNY, USA), Suvashis Maity, L. Sriramkumar (Indian Insitute of Technology, Madras, India)
The Borde-Guth-Vilenkin (BGV) theorem states that any spacetime with net positive expansion must be geodesically incomplete. We derive a new version of the theorem using the fluid flow formalism of General Relativity.

The theorem is purely kinematic, depending on the local expansion properties of geodesics, and makes no assumptions about energy conditions. We discuss the physical interpretation of this result in terms of coordinate patches on de Sitter space, and apply the theorem to Penrose's model of Conformal Cyclic Cosmology. We argue that the Conformal Cyclic extension of an asymptotically de Sitter universe is geodesically incomplete.
 

Similar threads

Replies
16
Views
1K
Replies
2
Views
1K
  • Cosmology
Replies
1
Views
1K
Replies
3
Views
1K
Replies
4
Views
875
Replies
10
Views
2K
Replies
19
Views
643
Replies
4
Views
926
Back
Top