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December 14, 2007
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Ten Years of the Accelerating Universe

Toward the end of 1997 word began to circulate among a small group of scientists — astronomers, cosmologists, experimental and theoretical physicists — that a strange message was incoming from the far reaches of the universe.

Since the 1930s, following the discovery that the universe is expanding, astronomers had wanted to use distant supernovae, exploding stars, as "standard candles" to measure the rate of expansion. Attempts failed repeatedly, and by the last quarter of the century most astronomers were discouraged. In the late 1980s and early 1990s, however, a group of particle physicists and astronomers based at Berkeley Lab began chipping away at the challenges — social as much as technical — that stood in the way of using supernovae to do cosmology.

Carl Pennypacker, who cofounded what would come to be known as the Supernova Cosmology Project (SCP), recalls that in the beginning, "the most striking part of the project was the huge skepticism. Nobody believed we could do it, and it was an enormous challenge to get things done." It took six years of dogged effort for the SCP to break through the biggest roadblock by proving they could use big telescopes to find distant "supernovae on demand."

Inspired by their success, a rival team of astronomers, the High-Z Supernova Search Team, now rushed to adapt the SCP's methods, hoping to be first to reach the scientific goal: the most precise measurement yet of how much the expansion of the universe was slowing down.

Except it wasn't slowing down....

This "crazy result" was the rumor that began circulating as members of both teams talked among themselves and their colleagues in the fall of 1997. In a recent issue of Physics World, historian and philosopher of science Robert Crease recounts the chronology of these events; since the word went public, Crease reports, "the leaders of the SCP and High-Z teams have worked together amiably and smoothly." Nevertheless, who did and said what, and when, is still debated among some members of the rival teams.

Saul Perlmutter, leader of the Supernova Cosmology Project, made the first public announcement of evidence for a cosmological constant — the universe-filling energy that counteracts gravitational collapse and accelerates expansion — at the meeting of the American Astronomical Society in Washington, D.C., in January, 1998. Within a few short weeks, cosmologist Michael Turner had introduced a simpler, more inclusive phrase: dark energy.

In this issue Science@Berkeley Lab celebrates the 10th anniversary of the announcement of what is now called dark energy. If you have any questions about our articles on dark energy, or any other topic, just drop us a line.

Science@Berkeley Lab appears about six times a year. Regular writers are Lynn Yarris, Paul Preuss, and Dan Krotz in the Communications Department and Allen Chen in the Environmental Energy Technologies Division. We get contributions from David Gilbert of the DOE Joint Genome Institute and writers from other departments as well. In the Creative Services Office (CSO), Erik Richman is our web developer, Roy Kaltschmidt is our photographer, and Eva Cohen did the original Science@Berkeley Lab design. Reid Edwards heads the Lab's Public Affairs Office, Ron Kolb heads the Communications Department, and Cheryl Ventimiglia heads CSO.

Paul Preuss, Editor, Science@Berkeley Lab