Three Harvard alumni have been awarded the Nobel Prize in Physics for their discoveries pertaining to the accelerating expansion of the universe through observations of distant supernovae. The trio are: Saul Perlmutter ’81, professor of physics at University of California, Berkeley, an astrophysicist at Lawrence Berkeley National Laboratory and leader of the international Supernova Cosmology Project; Brian P. Schmidt, Ph.D. ’93, now at the Australian National University (formerly known as the Mount Stromlo and Siding Spring Observatories); and Adam G. Riess, Ph.D. ’96, professor of astronomy and physics at Johns Hopkins University and the Space Telescope Science Institute. One-half of the prize is awarded to Perlmutter, and the other half is shared by Schmidt and Riess.
According to the Nobel press release,
What will be the final destiny of the Universe? Probably it will end in ice, if we are to believe this year's Nobel Laureates in Physics. They have studied several dozen exploding stars, called supernovae, and discovered that the Universe is expanding at an ever-accelerating rate. The discovery came as a complete surprise even to the Laureates themselves.
In 1998, cosmology was shaken at its foundations as two research teams presented their findings. Headed by Saul Perlmutter, one of the teams had set to work in 1988. Brian Schmidt headed another team, launched at the end of 1994, where Adam Riess was to play a crucial role.
The research teams raced to map the Universe by locating the most distant supernovae. More sophisticated telescopes on the ground and in space, as well as more powerful computers and new digital imaging sensors…opened the possibility in the 1990s to add more pieces to the cosmological puzzle.
The teams used a particular kind of supernova, called type Ia supernova. It is an explosion of an old compact star that is as heavy as the Sun but as small as the Earth. A single such supernova can emit as much light as a whole galaxy. All in all, the two research teams found over 50 distant supernovae whose light was weaker than expected—this was a sign that the expansion of the Universe was accelerating. The potential pitfalls had been numerous, and the scientists found reassurance in the fact that both groups had reached the same astonishing conclusion.
For almost a century, the Universe has been known to be expanding as a consequence of the Big Bang about 14 billion years ago. However, the discovery that this expansion is accelerating is astounding. If the expansion will continue to speed up the Universe will end in ice.
The acceleration is thought to be driven by dark energy, but what that dark energy is remains an enigma - perhaps the greatest in physics today. What is known is that dark energy constitutes about three quarters of the Universe. Therefore the findings of the 2011 Nobel Laureates in Physics have helped to unveil a Universe that to a large extent is unknown to science. And everything is possible again.
Schmidt’s website includes “The Accelerating Universe: an explanation for the interested non-scientist,” which includes beautifully illustrated animations untangling the mysteries of the Hubble constant, curvature in the universe, and the use of supernovae as points to measure the size of the universe and its rate of expansion.
For perspective on the discoveries, read this New York Times opinion piece by Clowes professor of science Robert P. Kirshner, under whom Schmidt and Riess studied as graduate students. Read the New York Times summary of the scientists' discoveries.
