Adam Riess, an astronomer at the Space Telescope Science Institute (STScI) and a professor in physics and astronomy at The Johns Hopkins University, today was awarded the 2011 Einstein Medal by the Albert Einstein Society, located in Bern, Switzerland. The Society recognized him for leadership in the High-z Supernova Search Team's 1998 discovery that the expansion rate of the universe is accelerating, a phenomenon widely attributed to a mysterious, unexplained "dark energy" filling the universe.
Riess (pronounced "Reese"), 40, shares this year's prize with Saul Perlmutter, an astrophysicist at the University of California, Berkeley, and the Lawrence Berkeley National Laboratory. Perlmutter's Supernova Cosmology Project team published similar results shortly after those published by Riess and High-z team member Brian Schmidt of the Australian National University. Both teams shared the Peter Gruber Foundation's 2007 Cosmology Prize — a gold medal and $500,000 — for the discovery of dark energy, which Science Magazine called "The Breakthrough Discovery of the Year" in 1998. The researchers also shared the 2006 Shaw Prize in astronomy for the same discovery.
The medal is awarded for outstanding scientific findings, works, or publications related to Albert Einstein. Physicist Stephen Hawking received the first Einstein Medal in 1979. The Albert Einstein Society was founded in 1977 to publicize Einstein's life and work during his years in Switzerland and especially in Bern. Riess will receive the medal at a ceremony in Bern in May 2011.
Riess thanked the Einstein Society and said, "The discovery of the acceleration of the universe and its implications for the presence of dark energy suggests we indeed live in an interesting time. Although Einstein is considered the intellectual godfather of this discovery, I think even he would have been surprised to see it. As for me, I have been very fortunate to work with tremendous colleagues and powerful facilities."
Riess led the study for the High-z Supernova Search Team of highly difficult and precise measurements — across 7 billion light-years — that resulted in the remarkable 1998 discovery that many believe has changed astrophysics forever: an accelerated expansion of the universe propelled by dark energy.
"We originally set out to use a special kind of exploding star called 'supernovae' to measure how fast the universe was expanding in the past and to compare it to how fast it is expanding now," Riess remembered. "We anticipated finding that gravity had slowed the rate of expansion over time. But that's not what we found."
Instead, Riess's team was startled to discern that the rate of expansion was actually speeding up.
These startling observations sent the team back to the idea, first proposed by Albert Einstein, that the so-called vacuum of space might produce a sort of "anti-gravity" energy that could act repulsively, accelerating the expansion of the universe.
"Suddenly, that idea made sense," said Riess. However, exactly what dark energy is and how it behaves remain among the most pressing questions in astrophysics today.
"One of the most exciting things about dark energy is that it seems to live at the very nexus of two of our most successful theories of physics: quantum mechanics, which explains the physics of the small, and Einstein's Theory of General Relativity, which explains the physics of the large, including gravity," he said.
"Currently, physicists have to choose between those two theories when they calculate something. Dark energy is giving us a peek into how to make those two theories operate together. Nature somehow must know how to bring these both together, and it is giving us some important clues. It's up to us to figure out what [those clues] are saying." Riess and his team are trying to measure dark energy's two most fundamental properties: how stable it is and how it has changed with the evolving universe.
Riess is continuing his Hubble Space Telescope observations of distant supernovae to characterize dark energy. He also is involved in searching for the exploding stars with the Panoramic Survey Telescope and Rapid Response System, a series of ground-based telescopes at the University of Hawaii's Institute for Astronomy. The sky survey is expected to find thousands of new supernovae.
In another method, Riess and his team, called SH0ES (Supernovae, H0, for the Equation of State), are analyzing pulsating stars, called Cepheid variables, with the Hubble telescope to refine the measurement of the universe's expansion rate. The new results are placing constraints on the properties of dark energy.
Lisa De Nike
The Johns Hopkins University, Baltimore, Md.