Andrei Linde - Cosmological Phase Transitions and Old Inflation

Cosmological Phase Transitions and Old Inflation

In 1972-1976, David Kirzhnits and Andrei Linde developed a theory of cosmological phase transitions. According to this theory, there was not much difference between weak, strong and electromagnetic interactions in the very early universe. These interactions became different from each other only gradually, after the cosmological phase transitions while the universe expanded and cooled down. In 1974 Linde found that the energy density of scalar fields breaking symmetry between different interactions can play the role of the vacuum energy density (cosmological constant) in the Einstein equations. In 1976-1978 he demonstrated that the release of this energy during the cosmological phase transitions may be sufficient to heat up the universe.

These observations became the main ingredients of the first version of the inflationary universe theory, which was proposed by Alan Guth in 1980. This theory, which is now called "old inflation," was based on the assumption that the universe was initially hot. It then experienced the cosmological phase transitions and was temporarily stuck in a supercooled metastable vacuum state (false vacuum). Then the universe expanded exponentially (inflated) until the false vacuum decayed, and the universe became hot again. This idea attracted lots of attention because it could provide a unique solution to many difficult problems of the standard Big Bang theory. In particular, it could explain why the universe is so large and so uniform. However, as Guth immediately realized, this scenario did not quite work as intended: the decay of the false vacuum would make the universe extremely inhomogeneous.