2009 Isaac Newton medal of the Institute of Physics

Professor Alan H Guth

Massachusetts Institute of Technology

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.

In 1981 Alan Guth proposed that many features of our universe, including how it came to be so uniform and why it began so close to the critical density, can be explained by a new cosmological model which he called inflation. Inflation is a modification of the conventional big bang theory, proposing that the expansion of the universe was propelled by a repulsive gravitational force generated by an exotic form of matter.

Through his invention of the inflationary universe model, Alan Guth has changed the way that cosmologists view the universe. Motivated by ideas of grand unified theories that attempt to unite the electromagnetic and nuclear forces, Professor Guth explored the cosmological consequences of a hypothetical new substance called the false vacuum.

Working with Henry Tye, he first showed that supercooling at the grand unified phase transition would suppress the production of otherwise disastrous magnetic monopoles predicted by grand unified theories. Professor Guth then realised that the supercooling would produce a false vacuum which in turn could an exponential expansion that could neatly solve two puzzles of then-standard cosmology: why the cosmic microwave background radiation is so smooth in different directions (the horizon problem) and why the universe is so large and spatially flat (the flatness problem).

Before Guth’s work, these issues in cosmology were generally regarded as metaphysical questions. His theory neatly solved them and it now underlies the standard model of cosmology.