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October 4, 2011

Nobel Prize In Physics

Awards: Three share honor for discovering accelerating expansion of the universe

Elizabeth K. Wilson

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Roy Kaltschmidt/LBNL
Perlmutter

Belinda Pratten/Australian National U
Schmidt

Johns Hopkins U
Reiss

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

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 a 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, 42, who work with the High Z Supernova Search Team, an international consortium, will share the other half.

"It feels like when my children were born—I'm weak in the knees," said Schmidt, who was reached by phone at home in Canberra, Australia, by members of the Nobel Committee during their press conference to announce the winners of the physics prize. Schmidt is a professor at the 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, Nobel Committee member Olga Botner explained at the conference. 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 parasitic dying stars, known as white dwarves. Originally the size of our sun, the white dwarves have spent most of their fuel and collapsed to the size of Earth. The intense gravity of white dwarves sucks material from any neighboring star, until they reach 1.44 solar masses. At this point, the dwarves explode massively and brilliantly, yielding objects known as supernovae 1a.

Because the luminosity of supernova 1a explosions is always the same, 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—the last one visible with the naked eye occurred in 1572. But with the advent of state of the art telescopes, combined with cameras based on charge-coupled devices (the development of which won the Physics Nobel in 2009), tens of supernovae 1a can be found within a single telescope scan.

For years, the two teams were in hot competition to prove what they thought they would discover—that the universe's expansion was in fact decelerating. But the brightnesses of distant supernovae 1a were much weaker than they should have been, if that were the case. Instead, both teams came to the conclusion that the universe's expansion is accelerating, which they announced in 1998. At the Nobel Committee press conference, Schmidt described the "trepidation in telling the world we had such a crazy result. We were hoping everyone would be nice to us." And as the award indicates, indeed they were.

Chemical & Engineering News
ISSN 0009-2347
Copyright © 2011 American Chemical Society
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