Stability in Cosmology, from Einstein to Inflation

Abstract

I investigate the role of stability in cosmology through two episodes from the recent history of cosmology: (1) Einstein's static universe and Eddington's demonstration of its instability, and (2) the flatness problem of the hot big bang model and its claimed solution by inflationary theory. These episodes illustrate differing reactions to instability in cosmological models, both positive ones and negative ones. To provide some context to these reactions, I also situate them in relation to perspectives on stability from dynamical systems theory and its epistemology. This reveals, for example, an insistence on stability as an extreme position in relation to the spectrum of physical systems which exhibit degrees of stability and fragility, one which has a pragmatic rationale, but not any deeper one.

On the Observation of Distant Objects in General Relativity and its Implications in Cosmology

“…However, this kind of non-local perturbation is non-physical in nature and it is still not clear today if the Einstein world is indeed unstable against perturbations having physical relevance. We defer to the very interesting chapter [3] for a detailed discussion of the matter. The discovery, by Hubble, of a linear relation between the redshift of galaxies and their distances [4] achieved to convince Einstein, at the beginning reluctant, to change his mind and accept the growing consensus on models based on expansion of space [5,7,8].…”