Stability in Cosmology, from Einstein to Inflation

I inquire into the role of stability in cosmology by investigating 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 alleged 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 situate them in relation to perspectives on stability from dynamical systems theory and its epistemology. This reveals, among other things, that an insistence on stability is an extreme position in light of the broad spectrum of physical systems exhibiting degrees of both stability and fragility, one which has perhaps a pragmatic rationale but not any deeper one.