The Quest for Dark Energy: High Road or Low?

摘要

Seven years ago, astrophysicists asked a simple question: "How far?" The answer overturned our understanding of the cosmos. Since 1929, researchers had known that the universe is expanding. But they assumed the expansion is slowing as the universe's own gravity tugs against it. Two teams set out to observe the slowing by measuring the distances to exploding stars known as super-novae. To the researchers' surprise, the farthest supernovae were farther than expected. That meant the expansion of the universe is accelerating as if driven by some weird space-stretching "dark energy." "When we first saw the result, I assumed our data was miscali-brated," recalls Saul Perlmutter of Lawrence Berkeley National Laboratory and the University of California, Berkeley. But within a few years, studies of the afterglow-of the big bang—the "cosmic microwave background"—and other measurements bolstered the case for dark energy and showed that it accounts for a whopping two-thirds of the universe. "The amazing thing about this discovery is how quickly people accepted it," Perlmutter says.