For his entire career, astronomer Dan Werthimer has been immersed in the search for extraterrestrial intelligence (SETI), watching the field grow from an eccentric hobby to a respectable scientific discipline, with government funding, conferences and grad students. What it still lacks, though, is a subject matter. "I've been looking for aliens for 28 years, and I haven't bagged one yet," he admits. Paradoxically, the field is awash in data--uncountable terabytes of it, virtually all of it meaningless, including four years' worth of random radio noise recorded by the 1,000-foot dish antenna at Arecibo, in Puerto Rico. Not even the world's fastest supercomputer could make sense of it all. So Werthimer, along with computer scientist David Anderson at Berkeley's Space Sciences Laboratory, enlisted a network of home and office desktop computers to sift through this vast electronic midden heap in search of one tiny artifact of civilization. More than 4 million people have lent their computers' downtime to this project, known as SETI@Home. Next week Werthimer, chief scientist for SETI@ Home, will begin assessing the fruits of that effort. His expectations are, frankly, infinitesimal. But you don't go into this field unless you're an optimist.
The effort is admirable, in any case. Beginning in 1998, while Arecibo traversed the sky observing pulsars and quasars, it also monitored a range of frequencies in the UHF band, centered on 1420 megahertz. "We didn't get to say where the telescope points," Werthimer says, "but that's OK, because nobody knows where to look anyway." The recordings made at Arecibo were chopped into 107-second segments and sent over the Internet to volunteers who had downloaded SETI@Home's screen-saver program. At idle moments the program kicks in, sifting through the raw data for signals that stand out from the background sounds of the universe going about its business. About 4 billion candidate signals were identified in this process, and edited down to the 200 of greatest interest. Next week, for the first time, the project will have 24 hours of dedicated time at Arecibo to look for those 200 signals again, on the remote possibility that even one of them shows signs of an extraterrestrial intelligence at work. "It's the kind of search any intelligent society has to do," says Bruce Murray, chairman of the Planetary Society, which helps fund SETI@Home. "But you can't do it with the expectation that you're actually going to find something."
Tremendous ingenuity went into choosing the 200 candidates and weeding out the billions that could be anything from radio-emitting galaxies to nearby car ignitions. The criteria included signals with a single point source (which could be a planet); signals concentrated on one frequency (like a radio transmission), and pulsed signals (which might signify information). The whole enterprise, however, rests on two leaps of faith: that alien civilizations exist and want to communicate with us, and that they will choose, among a near-infinite number of possibilities, the particular frequency we have chosen to listen on. It happens to be the frequency at which hydrogen absorbs and emits radio waves--"kind of the resonant frequency of the universe," says Anderson--so there is a theoretical justification for it. But who knows whether aliens will have the same insight? Werthimer puts the odds of success from next week's observations at "one in 10,000." But remember: he's an optimist.