Cyclic multiverses

TL;DR

This paper explores cyclic universe models with varying fundamental constants, proposing regularised non-singular bounces and extending the concept to multiverses with different entropy behaviors, including potential universe exchanges.

Contribution

It introduces models of cyclic universes with varying gravitational constants that regularise singularities and extends the framework to multiverses with different entropy evolution and universe exchange possibilities.

Findings

Two models of non-singular oscillating universes with varying G.

Multiverse scenarios with different entropy behaviors.

Potential universe exchange at maximum expansion points.

Abstract

Using the idea of regularisation of singularities due to the variability of the fundamental constants in cosmology we study the cyclic universe models. We find two models of oscillating and non-singular mass density and pressure ("non-singular" bounce) regularised by varying gravitational constant $G$ despite the scale factor evolution is oscillating and having sharp turning points ("singular" bounce). Both violating (big-bang) and non-violating (phantom) null energy condition models appear. Then, we extend this idea onto the multiverse containing cyclic individual universes with either growing or decreasing entropy though leaving the net entropy constant. In order to get an insight into the key idea, we consider the doubleverse with the same geometrical evolution of the two "parallel" universes with their physical evolution (physical coupling constants $c(t)$ and $G(t)$) being different. An interesting point is that there is a possibility to exchange the universes at the point of maximum expansion -- the fact which was already noticed in quantum cosmology. Similar scenario is also possible within the framework of Brans-Dicke theory where varying $G(t)$ is replaced by the dynamical Brans-Dicke field $\phi(t)$ though these theories are slightly different.