THE KAVLI PRIZE IN ASTROPHYSICS 2014

The Norwegian Academy of Science and Letters has decided to award the Kavli Prize in Astrophysics for 2014 to

Alan H. Guth Massachusetts Institute of Technology, Cambridge, MA, USA

Andrei D. Linde Stanford University, CA, USA

Alexei A. Starobinsky Landau Institute for Theoretical Physics, Russian Academy of Sciences, Moscow, Russia

“for pioneering the theory of cosmic inflation”

The theory of cosmic inflation, proposed astounding success, the Big Bang theory These two fundamental problems were and developed by Alan Guth, Andrei suffers from two major shortcomings: the elegantly solved in one fell swoop by Alan Linde and Alexei Starobinsky, has revo- “horizon” and the “flatness” problems. Guth in a paper entitled “Inflationary lutionized our thinking about the uni- Cosmic inflation solves them both. universe: A possible solution to the hori- verse. This theory extends our physical zon and flatness problems” published in description of the cosmos to the earliest As the universe expanded it cooled. Today 1981. Guth hypothesized that the uni- times, when the universe was only a tiny it is bathed in a sea of microwave radia- verse was initially trapped in a peculiar fraction of a second old. According to this tion, the heat left over from the Big Bang. state (the “false vacuum”) from which it theory, very soon after our universe came At first sight, the near uniformity of this decayed, in the process expanding expo- into existence it underwent a short-lived microwave background across the sky nentially and liberating the energy pres- phase of exponential expansion. During implies a disturbing contradiction: oppo- ent in our universe today. The phase of this brief period the universe expanded site parts of the sky would never have rapid expansion would have exposed dif- by a huge factor – hence the name infla- been in causal contact with each other. ferent parts of the universe to one tion. The consequences of this episode How could the properties of this radiation another, so that physical processes could were momentous for the evolution of the be so similar when no physical processes homogenize the properties of the primor- cosmos. could have acted to homogenize it? This dial radiation. This solved the horizon puzzle is known as the horizon problem. problem. The same expansion would Without inflation, the Big Bang theory A related puzzle is the flatness problem: have ironed out any primordial curvature, – a great achievement of 20th century if, at the Big Bang, the geometry of space thereby also solving the flatness problem. science – is incomplete. According to the had deviated ever so slightly from a flat However, Guth’s simple and elegant Big Bang theory our universe came into configuration, the curvature of the uni- model was flawed: as he himself recog- existence approximately 14 billion years verse would have subsequently been nized, it would lead to gross inhomoge- ago. Its initial density and temperature rapidly amplified. Yet, by the 1970s, neities in the distribution of matter on were unimaginably high. Since then, the astronomers were inferring that the large scales. universe has been expanding at a rate that geometry of our universe is close to flat. can be calculated using Einstein’s theory The Big Bang theory had no explanation In 1982 Andrei Linde proposed a working of General Relativity. In spite of its for this observation. model of inflation in which the universe The Norwegian Academy of Science and Letters Drammensveien 78, 0271 Oslo, Norway Phone +47 22 12 10 90 Fax +47 22 12 10 99 www.dnva.no

See also:

The Kavli Prize www.kavliprize.no

The Kavli Foundation www.kavlifoundation.org

would gracefully exit from the exponen- tial expansion phase without producing unacceptable inhomogeneities. He went on to build ever more sophisticated mod- els, which dominate current thinking in the field.

In 1980 Alexei Starobinsky indepen- dently postulated a similar early phase of exponential expansion, in this case driven by quantum gravity effects. The solution he devised included an important predic- tion: the early universe would have gener- ated gravitational waves which, he speculated, might one day be detected.

That the universe has a flat geometry has now been confirmed to extraordinary precision. With all its implications for the geometry and structure of our universe, the concept of cosmic inflation trans- formed the way in which physicists think about the early universe.