When the researchers launched SETI@Home, in May of ’99, they thought maybe 1,000 people might sign up. That number—and the bleaker view from outsiders, who said perhaps no one would join the crew—informed a poor decision: to set up a single desktop to farm out the data and take back the analysis.

But the problem was, people really liked the idea of letting their computers find aliens while they did nothing except not touch the mouse. And for SETI@Home’s launch, a million people signed up. Of course, the lone data-serving desktop staggered. SETI@Home fell down as soon as it started walking. Luckily, now-defunct Sun Microsystems donated computers to help the program get back on its feet. In the years since, more than 4 million people have tried SETI@Home. Together, they make up a collective computing power that exceeds 2008’s premier supercomputer.

But they have yet to find any aliens.

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SETI is a middle-aged science, with 57 years under its sagging belt. It began in 1960, when an astronomer named Frank Drake used an 85-foot radio telescope in Green Bank, West Virginia, to scan two Sun-like stars for signs of intelligent life—radio emissions the systems couldn’t produce on their own, like the thin-frequency broadcasts of our radio stations, or blips that repeated in a purposeful-looking way. Since then, scientists and engineers have used radio and optical telescopes to search much more of the sky—for those “narrowband” broadcasts, for fast pings, for long drones, for patterns distinguishing themselves from the chaotic background static and natural signals from stars and supernovae.

But the hardest part about SETI is that scientists don’t know where ET may live, or how ET’s civilization might choose to communicate. And so they have to look for a rainbow of possible missives from other solar systems, all of which move and spin at their own special-snowflake speeds through the universe. There’s only one way to do that, says Dan Werthimer, the chief SETI scientist at Berkeley and a co-founder of SETI@Home: “We need a lot of computing power.”

In the 1970s, when Werthimer’s Berkeley colleagues launched a SETI project called SERENDIP, they sucked power from all the computers in their building, then the neighboring building. In a way, it was a SETI@Home prototype. In the decades that followed, they turned to supercomputers. And then, they came for your CPUs.

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The idea for SETI@Home originated at a cocktail party in Seattle, when computer scientist David Gedye asked a friend what it might take to excite the public about science. Could computers somehow do something similar to what the Apollo program had done? Gedye dreamed up the idea of “volunteer computing,” in which people gave up their hard drives for the greater good when those drives were idle, much like people give up their idle cars, for periods of time, to Turo (if Turo didn’t make money and also served the greater good). What might people volunteer to help with? His mind wandered to The X-Files, UFOs, hit headlines fronting the National Enquirer. People were so interested in all that. “It’s a slightly misguided interest, but still,” says David Anderson, Gedye’s graduate-school advisor at Berkeley. Interest is interest is interest, misguided or guided perfectly.