Johns Hopkins University
Fall/Winter 2007
Vol. 5, No. 1


Pinpointing “Pockets of Hope”

> Cosmology’s Force to Be Reckoned With

Student Research From the Field


Total War: The Big Picture

Plumbing the Mysteries of the Mind

Embrace Your Inner Cynic

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Cosmology’s Force to Be Reckoned With

Adam RiessAccording to Adam Riess, "Everything we know about dark energy could be summarized on a fortune cookie strip."

His pithy summary: "That it's 70 percent of the energy and mass of the universe; that it's making the universe expand faster and faster all the time, and that understanding its nature is critical to our understanding the fate of our universe."

That may not sound like much, but it's far more than anyone knew before Riess and his team became the first to publish a paper (almost 10 years ago, in the September 1998 issue of Astrophysical Journal) showing that a previously unknown force dubbed "dark energy" is causing the universe to expand faster and faster.

For that discovery, the Krieger School professor of Physics and Astronomy recently won one of cosmology's most prestigious awards: the 2007 Gruber Cosmology Prize, administered by the Peter Gruber Foundation. The 37-year-old shares the prize's gold medal and $500,000 with members of his team (called the High-z Supernova Search Team) and with members of the Supernova Cosmology Project, a competing team led by Saul Perlmutter at the University of California, Berkeley, whose paper was published in 1999. Riess received the prize on Sept. 7 at the University of Cambridge.

This is Riess' second big cosmology prize for the "dark energy" body of work: Last year, he shared the $1 million Shaw Prize with Brian Schmidt of the Mount Stromlo Observatory of the Australian National University in Canberra and Perlmutter.

"Winning these prizes is a huge honor," says Riess, who is typically modest and low-key when asked to discuss his accomplishments, but waxes enthusiastic when talking about science. "But perhaps the most interesting aspect of this whole thing is that [our] results were so completely unexpected. We were as surprised by what we found as you would be if you tossed a ball into the air and instead of it coming down, it just kept floating up and up."

At the time, most astrophysicists-including Riess and his team-assumed that the universe's rate of expansion was slowing down due to gravity. Riess' aim was to use a special kind of exploding star called "supernovae" to measure how fast the universe expanded in the past to compare it to the rate of expansion now.

But their results revealed that expansion wasn't slowing down. It was accelerating. Riess was perplexed. Had he done something wrong? Were his mathematical calculations-across 7 billion light-years-amiss? No matter what he did, however, the result indicated the same thing: The universe's rate of expansion was speeding up.

"So we finally published the paper, figuring that someone else would find whatever mistake it was that we made, but that didn't happen," he explains.

In fact, since that discovery, Riess and his team's assertion has been verified by wholly independent measuring techniques. He and other experts in the field now refer to the phenomenon as "dark energy" and posit that it may account for up to 70 percent of the universe, "even though," he confesses, "we still don't understand it well at all." In fact, what dark energy is and how it behaves are 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," Riess says.

"Right now, physicists have to choose between these 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."