Alan Guth is a theoretical physicist and cosmologist, known mainly for his work on elementary particle theory and how particle theory is applicable to the early universe, and particularly for the idea, which he developed around 1980, of cosmic inflation and the inflationary universe, the idea that the nascent universe passed through a phase of exponential expansion soon after the Big Bang, driven by a positive vacuum energy density.
Alan Harvey Guth was born on 27 February 1947 in the small town of New Brunswick, New Jersey, USA, to a middle-class Jewish couple, Hyman and Elaine Guth, owners of a small grocery store and a dry-cleaning establishment. His early childhood was unremarkable, although he showed a strong aptitude for mathematics. After attending several public schools, he skipped his senior year to enrol in a five-year program at the Massachusetts Institute of Technology (MIT), partly because he was concerned about being drafted for the Vietnam War, of which he strongly disapproved. He obtained both his bachelor’s and master’s degree in 1969, and a doctorate in 1972.
In 1971, he married his high school sweetheart, Susan Tisch, and they were to have two children: Lawrence (1977) and Jennifer (1983). However, after graduating, Guth had a hard time finding a permanent job, partly because of the intense competition for university professor positions due to the baby boom, and he spent nine years travelling across the country pursuing temporary post-doctorate jobs related to physics, including time spent at Princeton (1971 to 1974), Columbia (1974 to 1977), Cornell (1977 to 1979) and at the Linear Accelerator Center at Stanford (1979 to 1980).
His early focus at Princeton was on particle physics, particularly the study of quarks, the elementary particles that make up protons and neutrons. However, his research became obsolete with the development of the theory of quantum chromodynamics, ironically developed right there at Princeton, unknown to Guth, which gave quarks a new special property called “colour”.
In 1974, at Columbia, Guth turned more to cosmology and cosmogenesis, and particularly to work on magnetic monopoles (magnets with only one pole, which had been initially predicted in theory by James Clerk Maxwell’s equations, but were yet to be discovered in the real universe). Guth proposed that the process of spontaneous symmetry-breaking in the early universe described by Steven Weinberg’s “electroweak theory”, could produce very tiny discontinuities with the properties of magnetic monopoles.
He first started to develop his theory of cosmic inflation while at Cornell in 1978, when he was looking for solutions to the “flatness problem” of the Big Bang model of the universe, and to the problem he himself had identified, the apparent lack of magnetic monopoles. Once again he made use of earlier work by Steve Weinberg, namely his Grand Unified Theory (an attempt to unify the electromagnetic, weak and strong nuclear forces).
Guth’s proposed solution to these problems involved a very short but very rapid period of supercooling during a delayed phase transition, producing a “false vacuum” (an unstable, temporary state of the lowest possible density of energy). As a result of quantum tunnelling, the false vacuum would eventually decay into a low-energy true vacuum, and Guth found that the decay of the false vacuum at the beginning of the universe could produce some amazing results, including a rapid expansion at ever-increasing rates, which he called cosmic inflation.
The incredibly vast expansion of the universe caused by inflation “solved” both Robert Dickes flatness problem and Guth’s own monopole problem. However, it also solved the “horizon problem” of the Big Bang theory (the recent observation that the cosmic microwave background radiation appeared to be extremely uniform thoughout the universe, with almost no variance, which was paradoxical because there should not have been enough time at the time of the creation of the cosmic background radiation for one end of the cosmos to have been in communication with the other end). According to Guth’s inflation theory, however, the universe blew up so quickly that there was no time for the essential homogeneity to be broken, and the universe after inflation would therefore have been very uniform, even though the parts were not still in touch with each other.
Guth first released his ideas on cosmic inflation in a seminar at the Stanford Linear Accelerator Center in early 1980, and he went overnight from being worried about his job prospects to being besieged with offers. He returned to MIT in 1980, becoming professor of physics in 1986.
For some time, however, he could find no way to end inflation (so that stars and galaxies could form), often referred to as the "graceful exit" problem, and he considered his own theory something of a failure because of this. But, after he read a paper in late 1981 by the Russian physicist Andrei Linde (who had been working on the problem independently) and other work by Paul Steinhardt (who had also been working on the graceful exit problem), he began to exchange papers with these other theorists, thus helping each other work out inflation theory, and there have been many other refinements and revisions since Guth's original model.
More recently, Guth has expressed his belief that our universe is just one of many universes that came into existence among countless others as part of a multiverse. According to this theory, cosmic inflation never ends, but continues expanding at an exponential rate, with additional universes being created all the time as "bubbles" within the inflation process (in some ways similar to Fred Hoyle’s discredited steady-state theory). He believes that the entire cosmos was created by quantum fluctuations from nothingness (which he argues is perfectly consistent with the Law of Conservation of Energy because its total energy value remains zero), and is quoted as saying that “the universe is the ultimate free lunch”.
Guth continues to lecture at the Massachusetts Institute of Technology (MIT), and has written over 60 technical papers related to the effects of cosmic inflation and its interactions with particle physics. He has won many awards and medals, including the Medal of the International Center for Theoretical Physics and the Eddington Medal. His 1998 book, “The Inflationary Universe: The Quest for a New Theory of Cosmic Origins”, became a popular best-seller.