Nobel Prize In Physics

For the revolutionary discovery that the universe is expanding at an accelerating rate, three U.S.-born cosmologists—Saul Perlmutter, Adam G. Riess, and Brian P. Schmidt—have won the 2011 Nobel Prize in Physics.

The fact that the universe is expanding has been known for nearly a century. But it’s been only 13 years since the prizewinners discovered the increasing acceleration, which unseated the reigning theory that the universe was decelerating. The implications have been profound, requiring new models to determine the fate of the universe, as well as the invocation of a mysterious “dark energy” to drive the acceleration.

The prizewinners led two different teams. Perlmutter, 52, is head of the Supernova Cosmology Project at Lawrence Berkeley National Laboratory and will receive half of the approximately $1.5 million prize. Schmidt, 44, and Riess, 41, who work with the High-z Supernova Search Team, will share the other half.

“It feels like when my children were born—I’m weak in the knees,” said Schmidt, by phone at a press conference to announce the winners of the prize. Schmidt is a professor at Australian National University. Riess is an astronomy professor at Johns Hopkins University.

To explain the acceleration of the universe, cosmologists have turned to the idea of a “dark energy” that is propelling the universe outward at increasing speed. In fact, 95% of the universe is believed to be made of this yet-to-be-discovered dark energy and dark matter.

The astronomical objects that made this discovery possible are exploding stars known as supernovae 1a. Because all supernovae 1a have the same luminosity, their relative brightness can be used to compare their distance from each other. These measurements are key to calculating the rate of expansion of the universe.

Until recently, observations of supernovae 1a were too rare to make useful comparisons. But with the advent of telescopes equipped with charge-coupled devices, tens of supernovae 1a can be found within a single telescope scan.

The two teams found in separate studies that the brightnesses of distant supernovae 1a were much weaker than they should have been if the universe were decelerating. Instead, both teams came to the conclusion that the universe’s expansion is accelerating, which they announced in 1998.