Hard as it is for Earthlings to imagine, astronomers have known for some time that the universe is expanding. They've never been able to figure out, though, whether it will balloon outward forever or slow under the combined gravity of its 100 billion galaxies, stop and fall back in on itself. Thanks in large part to Adam Riess, they're a lot closer to an answer--and it's not what they expected.
Riess was only 25 when he joined a prestigious group of scientists who set out in 1995 to measure what was expected would be a post-Big Bang cosmic slowdown. The idea was to compare the expansion rate today with the rate billions of years ago by gauging the speeds of exploding stars called supernovas--Riess's grad-school specialty. But in January 1998, Riess saw something weird: the number he was getting for the slowdown kept coming out negative. The universe wasn't slowing down; it was speeding up! "This seemed to imply," he says, "that some force is acting against gravity." Crazy as antigravity sounds, the idea was originally suggested by Einstein as a kind of add-on to his General Theory of Relativity.
Riess's colleagues are most impressed with his willingness to challenge his own work. "Instead of making an emotional commitment to the accelerating universe," says Harvard's Robert Kirshner, one of the team's leaders, "Adam is always trying to see whether we've done things right."
Evidently they have. A second group came up with the same result at about the same time, and the journal Science named the accelerating universe Discovery of the Year for 1998. Riess, 30, now at the Space Telescope Science Institute in Baltimore, Md., is trying to push the observations beyond the edge. "In the past year," he says, "we've been finding supernovas further away than ever." Who knows what mysteries these distant beacons might reveal?
--By Michael D. Lemonick