Cosmic no-hair theorems for viscous contracting Universes

A cosmic no-hair theorem for all initially contracting, spatially homogeneous, orthogonal Bianchi Cosmologies is derived - which shows that all such Universes asymptote to a spatially flat, isotropic Universe with the inclusion of a shear viscous stress. This establishes a new mechanism of isotropisation in a contracting Universe, which does not take recourse to an ekpyrosis-like mechanism using an effective ultra-stiff equation of state fluid, that is, one in which the pressure is much greater than the energy density.

Automated summary

A new cosmic mechanism of isotropisation in a contracting Universe is established, which does not rely on an ekpyrosis-like mechanism using an effective ultra-stiff equation of state fluid. Instead, all initially contracting, spatially homogeneous, orthogonal Bianchi Cosmologies are shown to asymptote to a spatially flat, isotropic Universe with the inclusion of a shear viscous stress.