Chapter 4

Inflationary cosmology and creation of

matter in the universe

Andrei D Linde

Department of Physics, Stanford University, Stanford, USA

4.1 Introduction

The typical lifetime of a new trend in high-energy physics and cosmology is
nowadays about 5–10 years. If it has survived for a longer time, the chances
are that it will be with us for quite a while. Inflationary theory by now is 20
years old, and it is still very much alive. It is the only theory which explains
why our universe is so homogeneous, flat and isotropic, and why its different
parts began their expansion simultaneously. It provides a mechanism explaining
galaxy formation and solves numerous different problems at the intersection
between cosmology and particle physics. It seems to be in a good agreement
with observational data and it does not have any competitors. Thus we have some
reasons for optimism.
According to the standard textbook description, inflation is a stage of
exponential expansion in a supercooled false vacuum state formed as a result of
high-temperature phase transitions in Grand Unified Theories (GUTs). However,
during the last 20 years inflationary theory has changed quite substantially. New
versions of inflationary theory typically do not require any assumptions about
initial thermal equilibrium in the early universe, supercooling and exponential
expansion in the false vacuum state. Instead of this, we are thinking about chaotic
initial conditions, quantum cosmology and the theory of a self-reproducing
universe.
Inflationary theory was proposed as an attempt to resolve problems of the
big bang theory. In particular, inflation provides a simple explanation of the
extraordinary homogeneity of the observable part of the universe. But it can make
the universe extremely inhomogeneous on a much greater scale. Now we believe
that instead of being a single, expanding ball of fire produced in the big bang, the

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