From Big Crunch To Big Bang - Is It Possible?

TL;DR

This work asks whether a contracting flat space (big crunch) can smoothly transition to an expanding flat space (big bang) through a spacelike singularity within string theory. It combines a minisuperspace analysis of a simple gravity-scalar system with a higher-dimensional, radion-driven perspective, identifying a two-cone geometry ${\cal M}^2$ and a Milne-like sector that could interpolate between contraction and expansion. Several string/M-theory embeddings are proposed (e.g., $\mathbb{R}^9\times{\cal M}^2$, orbifolds, and circle compactifications) to realize or resolve the transition, suggesting that the singularity may be navigable in a UV-complete theory. If borne out, the idea implies a cosmology with no temporal origin and a pre-big-bang history, potentially informing pre-big-bang and ekpyrotic/cyclic models, but requires a rigorous nonperturbative string analysis to prove feasibility.

Abstract

We discuss the possibility of a transition from a contracting flat space - big crunch - to an expanding flat space - big bang.