Thinking about the Universe

Abstract

This article is largely a review and critical analysis of earlier papers by the author, and, within the broad background of the literature on this subject, it discusses the problems in the early stages of evolution of the Universe close to the singularity point. Special attention is paid to analyzing the properties of the de Sitter and Friedmann universes, and discussing the physical conditions which could induce a transition from one type of universe to another. Various modifications of the usual Einstein equations are presented which could serve as the dynamical basis of such a transition. A version of gravity in which the gravitational constant is replaced by a function of the matter (energy) density approaching zero as the density increases to its maximum value is discussed in detail. The possible nontrivial role of black holes during the inflationary stage of development of the Universe and also (for closed universes) during the final collapse stage is discussed. The possibility that the physical laws change in regions of space of size close to the Planck length, which could lead to the existence of a special physics of the ultra-microscopic world, is especially emphasized.