Properties of Information Carrying Waves in Cosmology

TL;DR

This paper proves that in isotropic cosmologies, information carrying waves universally induce shear and anisotropic stress, with explicit examples illustrating their essential role in wave perturbations.

Contribution

It establishes that all information carrying waves in isotropic cosmologies inherently produce shear and anisotropic stress, extending previous specific examples to a general proof.

Findings

Information carrying waves induce shear and anisotropic stress universally.

Explicit examples show the essential role of anisotropic stress in wave perturbations.

Null hypersurfaces of wave-fronts are shear-free in these scenarios.

Abstract

Recently we studied the effects of information carrying waves propagating through isotropic cosmologies. By information carrying we mean that the waves have an arbitrary dependence on a function. We found that the waves introduce shear and anisotropic stress into the universe. We then constructed explicit examples of pure gravity wave perturbations for which the presence of this anisotropic stress is essential and the null hypersurfaces playing the role of the histories of the wave-fronts in the background space-time are shear-free. Motivated by this result we now prove that these two properties are true for all information carrying waves in isotropic cosmologies.