Inhomogeneity and Anisotropy Generation in FRW Cosmologies

Summary

Abstract

Misner [1] suggested kinetic theory ideas could explain the smoothing of the universe at early times. Recently [2], [3] the inverse has been investigated: the generation of Bianchi I anisotropy in cosmologies with an exact FRW geometry, again for kinetic theory reasons. At the time it was stated that more general anisotropy and inhomogeneity could be generated by the same methods. In this paper the more general case is addressed to show how the model can be produced and to identify some open questions connected with it.

Introduction

One of the major contributions Charles Misner has made to cosmology was the first serious investigation of the chaotic cosmology idea [1], namely that the universe started off in a very chaotic state and then developed (by physical processes) towards a smooth state. This idea has since been taken up with a vengeance by the Inflationary Universe school of thought, utilising Guth's insight [4] that the vast expansion associated with the false vacuum (a scalar field) could provide the required smoothing mechanism.

The resulting theory is very interesting but perhaps over-stated [5]. In particular it does not overcome the Stewart remark [6] that no matter what smoothing mechanisms one might find there are always initial data that will lead to universes more lumpy than the observed universe (simply run the equations backwards from any considered present state to find the needed initial conditions). Furthermore entropy arguments have been adduced by Penrose [7] to suggest that the universe must have started off in a smooth state rather than the very chaotic state suggested by many inflationists.