The End

Monday, Jun. 25, 2001 By MICHAEL D. LEMONICK

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By 1998 both teams knew something very weird was happening. The cosmic expansion should have been slowing down a lot or a little, depending on whether it contained a lot of matter or a little--an effect that should have shown up as distant supernovas, looking brighter than you would expect compared with closer ones. But, in fact, they were dimmer--as if the expansion was speeding up. "I kept running the numbers through the computer," recalls Adam Riess, a Space Telescope Science Institute astronomer analyzing the data from Schmidt's group, "and the answers made no sense. I was sure there was a bug in the program." Perlmutter's group, meanwhile, spent the better part of the year trying to figure out what could be producing its own crazy results.

In the end, both teams adopted Sherlock Holmes' attitude: once you have eliminated the impossible, whatever is left, no matter how improbable, has got to be true. The universe was indeed speeding up, suggesting that some sort of powerful antigravity force was at work, forcing the galaxies to fly apart even as ordinary gravity was trying to draw them together. "It helped a lot," says Riess, "that Saul's group was getting the same answer we were. When you have a strange result, you like to have company." Both groups announced their findings almost simultaneously, and the accelerating universe was named Discovery of the Year for 1998 by Science magazine.

For all its seeming strangeness, antigravity did have a history, one dating back to Einstein's 1916 theory of general relativity. The theory's equations suggest that the universe must be either expanding or contracting; it couldn't simply sit there. Yet the astronomers of the day, armed with relatively feeble telescopes, insisted that it was doing just that. Grumbling about having to mar the elegance of his beloved mathematics, Einstein added an extra term to the equations of relativity. Called the cosmological constant, it amounted to a force that opposed gravity and propped up the universe.

A decade later, though, Edwin Hubble discovered that the universe was expanding after all. Einstein immediately and with great relief discarded the cosmological constant, declaring it to be the biggest blunder of his life. (If he had stuck to his guns, he might have nabbed another Nobel.)

Even so, the idea of a cosmological constant wasn't entirely dead. The equations of quantum physics independently suggested that the seemingly empty vacuum of space should be seething with a form of energy that would act just like Einstein's disowned antigravity. Problem was, this force would have been so powerful that it would have blown the universe apart before atoms could form, let alone galaxies--which it clearly did not. "The value particle physicists predict for the cosmological constant," admits Chicago's Turner, "is the most embarrassing number in physics."