Discovering Dark Energy

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In the mid-1990s, two teams of astronomers were trying to decide how the universe would end. Some thought it would all mash together in a Big Crunch. Others predicted that it would keep expanding, but at a slower rate. But instead, in results that were published 10 years ago, the teams found that the universe will expand forever, at an ever-increasing pace.

The teams had discovered dark energy -- a discovery that means that our understanding of the universe is far from complete.

The astronomers were measuring exploding stars in distant galaxies to see how quickly the expansion rate of the universe was slowing down. But a member of one of the teams, Adam Riess, says they got a surprise:

RIESS: I had sort of phrased the question to the computer as "˜What is the mass required to cause the deceleration' I assumed was present in the data. And the computer...says "˜Gee, I can't fit that. But I could switch the sign and make the mass negative, because that's what I need.' Well, there's no such thing as negative mass, but there is negative deceleration.... That's really acceleration.

Saul Perlmutter, the leader of the other team, summarizes what the findings mean about the expanding universe:

PERLMUTTER: What we found out was that it's not slowing enough to come to a halt, and in fact it's not slowing at all, but in fact it's speeding up, and that was obviously the big surprise, at the end of 1997, when we saw these results.

More about dark energy tomorrow.

Script by Damond Benningfield, Copyright 2008

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