Comments on Inflationary Cosmology

In this talk we will discuss three different issues. First of all, there exist several proposals how to solve cosmological problems by adiabatic expansion of the Universe of a specific type, without any use of inflation. We explain why these models do not solve the flatness/entropy problem. On the other hand there exist some claims that inflation also does not solve the flatness problem. We show that these claims are correct to a certain extent for old and new inflation, but are incorrect for simplest versions of chaotic inflation. The second issue to be considered is the classification of inflationary models. At present all kinds of inflationary models are compared to each other in order to understand which of them better describes observational data. Unfortunately, this often leads to terminological misunderstandings and even to misleading conclusions. We discuss three coexisting types of classification of inflationary models and explain their relation to each other. We also briefly describe the hybrid inflation model, which combines several interesting features of different inflationary models. Finally we show that it is possible to describe inflationary universe by a stationary (i.e. time-independent) probability distribution to find a domain of a given size containing matter with given properties. This represents a strong deviation of inflationary cosmology from the standard Big Bang paradigm. Based on the talks given at the 5th Canadian Conference on General Relativity, Waterloo, at the Yamada Conference on Cosmology, Tokyo, and at the Summer School on Cosmology in Aspen, 1993 On leave from: Lebedev Physical Institute, Moscow. E-mail: [email protected]