Andrei Dmitriyevich Linde (; born March 2, 1948) is a Russian-American theoretical physicist and the Harald Trap Friis Professor of Physics at Stanford University. Linde is one of the main authors of the inflationary universe theory, as well as the theory of eternal inflation and inflationary multiverse. He received his Bachelor of Science degree from Moscow State University. In 1975, Linde was awarded a PhD from the Lebedev Physical Institute in Moscow. He worked at CERN (European Organization for Nuclear Research) since 1989 and moved to the United States in 1990, where he became professor of physics at Stanford University. Among the various awards he has received for his work on inflation, in 2002 he was awarded the Dirac Medal, along with Alan Guth of MIT and Paul Steinhardt of Princeton University. In 2004 he received, along with Alan Guth, the Gruber Prize in Cosmology for the development of inflationary cosmology. In 2012 he, along with Alan Guth, was an inaugural awardee of the Fundamental Physics Prize. In 2014 he received the Kavli Prize in Astrophysics "for pioneering the theory of cosmic inflation", together with Alan Guth and Alexei Starobinsky. In 2018 he received the Gamow Prize. Cosmological phase transitions and old inflation During 1972 to 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 which happened when the temperature in the expanding Universe's became sufficiently small. In 1974, Linde found that the energy density of scalar fields that break the symmetry between different interactions can play the role of the vacuum energy density (the cosmological constant) in the Einstein equations. Between 1976 and 1978, Linde 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 proposed by Alan Guth in 1980. This theory, now called the "Old inflation theory", 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 (a false vacuum). The universe then expanded exponentially – "inflated" – until the false vacuum decayed and the universe