Alan Guth, the Victor F. Weisskopf Professor of Physics at MIT, was awarded the Kavli Prize in Astrophysics, announced yesterday by the Kavli Foundation in Oslo, linked by satellite to a session at the World Science Festival in New York.
Guth will share the $1 million prize with Andrei Linde of Stanford University and Alexei Starobinsky of the Landau Institute for Theoretical Physics in Russia. Together, they are cited by the Kavli Foundation “for pioneering the theory of cosmic inflation.”
Guth proposed the theory of cosmic inflation in 1980, the same year he joined the MIT faculty. The theory describes a period of extremely rapid exponential expansion within the first infinitesimal fraction of a second of the universe’s existence. At the end of inflation, approximately 14 billion years ago, the universe was in an extremely hot, dense, and small state, at the beginning of the more leisurely phase of expansion described by the conventional “Big Bang” theory. The conventional theory most successfully explains what happened after the bang, describing how the universe has cooled with expansion and how its expansion has been slowed by the attractive forces of gravity.
However, the conventional theory does not describe the mechanism that propelled the expansion of the universe in the first place, but the theory of cosmological inflation does: Guth hypothesized that the expansion of the universe was driven by repulsive gravitational forces generated by an exotic form of matter. Supported by three decades of development, including contributions from Linde, Andreas Albrecht, and Paul Steinhardt, Guth’s theory is now widely accepted by physicists.
The theory was further supported by an announcement in March by astronomers working on the Background Imaging of Cosmic Extragalactic Polarization telescope, which discovered evidence of gravitational waves produced by inflation. This experiment, however, has not yet been confirmed.
Cosmological inflation builds on general relativity’s description of gravity as a distortion of space-time, which allows for the possibility of repulsive gravity. At very high energies, like those that existed at the beginning of the universe, modern particle theory suggests that forms of matter that generate repulsive gravity should exist.
Inflation posits that this material inhabited at least a very small part of the universe, perhaps no more than 10-24 centimeters across, 100 billion times smaller than a proton. As the material began to expand, doubling every 10-37 seconds, any normal matter would thin out to a density of nearly zero.
Repulsive-gravity material behaves very differently, however, maintaining a constant density as it expands. While appearing to violate the principle of the conservation of energy, the constant density is enabled by an unusual feature of gravity: The energy of a gravitational field is negative.
As repulsive-gravity material exponentially expanded in the early universe, it created more and more energy in the form of matter. In turn, the gravitational field generated by matter created more and more negative energy. The total energy remained constant. When inflation ended, the repulsive-gravity material decayed into a hot soup of the ordinary particles that would be the starting point for the conventional Big Bang.
Awarded in alternating years since 2008, the Kavli Prize recognizes outstanding scientific achievements in the categories of astrophysics, nanoscience, and neuroscience. Guth, along with this year’s eight other recipients, will be presented with the award by King Harald of Norway at a ceremony in Oslo on Sept. 9.
The Kavli Prize was established in 2005 by the founder of the Kavli Foundation, Fred Kavli, as well as Kristin Clemet, Norway’s minister of education and research, and Jan Fridthjof Bernt, president of the Norwegian Academy of Science and Letters. Before the prize was established, Guth met Kavli several times, including at a dinner Kavli organized to discuss his philanthropic goals with a contingent of physicists. While opinions at the table differed, the group advised him against establishing the Kavli Prize.
“I don’t think I voiced an opinion on that subject,” Guth says, “but now I’m glad that we didn’t talk him out of it. I now think that prizes of this sort actually do help to put scientists in the spotlight, and that helps to elevate the status of scientists in the eyes of young people choosing careers. Nobody should go into science for the money, but it is important that science is viewed as something valued by society. Through the prizes and also through his funding of Kavli Institutes around the world, including at MIT, Fred Kavli has been crucially important in furthering the cause of science.”
Guth’s previous honors include election to the National Academy of Sciences and the American Academy of Arts and Sciences; the Franklin Medal for Physics from the Franklin Institute; the Dirac Prize from the International Center for Theoretical Physics; the Cosmology Prize from the Peter Gruber Foundation; the Newton Prize of the Institute of Physics (U.K.); and the Fundamental Physics Prize of the Milner Foundation.