We consider a class of globally hyperbolic space-times with "expanding singularities". Under suitable assumptions we show that no -extensions across a compact boundary exist, while the boundary must be null wherever differentiable (which is almost everywhere) in the non-compact case.
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The study of low regularity (in-)extendibility of Lorentzian manifolds is motivated by the question whether a given solution to the Einstein equations can be extended (or is maximal) as a weak solution. In this paper we show that a timelike complete and globally hyperbolic Lorentzian manifold is -inextendible. For…
Study shows cohomological limits on extending actions on 3-manifold boundaries.
problem Limits to extending group actions on 3-manifold boundaries.
method Cohomological obstructions for -actions on -manifolds.
result Cohomological obstructions prevent extending actions on certain 3-manifold boundaries.
The existence, established over the past number of years and supporting earlier work of Ori [14], of physically relevant black hole spacetimes that admit metric extensions beyond the future Cauchy horizon, while being -inextendible, has focused attention on fundamental issues concerning the strong cosmic cen…
Milne-like spacetimes are a class of FLRW models which admit spacetime extensions through the big bang. The boundary of a Milne-like spacetime can be identified with a null cone in the extension. We find that the comoving observers all emanate from a single point in the extension. This suggests that something phy…