The cosmologist Alan Guth has won the 2009 Isaac Newton medal of the Institute of Physics. The American physicist was honoured for “his invention of the inflationary universe model, his recognition that inflation would solve major problems confronting then-standard cosmology, and his calculation, with others, of the spectrum of density fluctuations that gave rise to structure in the universe”.

The Isaac Newton medal includes a £2000 prize and is awarded for “outstanding contributions to physics”. It will be presented at a ceremony in London on 15 October and Guth will deliver the Institute’s 2009 Isaac Newton Lecture on 13 October.

In 1981, Guth introduced the concept of an inflationary universe to address a number of flaws in the conventional big-bang theory of the origin of the universe. According to the inflationary concept, the universe underwent a fantastic burst of hyperexpansion during the first instants after the big bang, stretching unimaginably faster than the conventional picture would predict.

Important questions

This hyperexpansion answered two important questions facing cosmologists at the time: why energy is spread so uniformly throughout the universe and how tiny deviations from perfect uniformity can arise. These deviations eventually led to the formation of galaxies and large-scale structure.

Guth came up with the idea of inflation when he was looking at a phase transition that is believed to have occurred about 10^-35 s after the big bang — when the strong force separates from the electroweak force. Grand unified theories had predicted that vast numbers of magnetic monopoles would be created at this time, but there is no observational evidence that this happened.

Working with Henry Tye of Cornell University, Guth realized that theories of particle physics and cosmology could be modified such that a supercooling of the universe occurs at the phase transition — suppressing the production of the monopoles. This supercooling also unleashed a tremendous amount of energy, which accelerated the expansion of the universe in an inflationary period lasting about 10^-32 s.

Inflation theory remains an important milestone in the development of cosmology because it showed that the nature of the universe as a whole could be understood in terms of theories derived from particle physics experiments.

Guth, 62, was born in New Jersey and is Victor F Weisskopf Professor of Physics at the Massachusetts Institute of Technology — which he joined in 1980.