For more than two decades, millions of volunteers around the world contributed their home computers to help University of California Berkeley scientists search for extraterrestrial life. The project, known as SETI@home, operated from 1999 to 2020 and analyzed radio signals captured by the Arecibo Observatory in Puerto Rico.
Participants downloaded software that allowed their computers to process data looking for unusual signals from space. According to David Anderson, computer scientist and co-founder of the project, these efforts produced 12 billion detections—brief bursts of energy at specific frequencies from particular points in the sky.
After ten years of analysis, researchers narrowed down these detections to about one million candidate signals and then further reduced them to 100 that merit additional study. Since July, the team has been using China’s Five-hundred-meter Aperture Spherical Telescope (FAST) to re-examine these targets.
Anderson noted that while results from FAST are still pending, he does not expect a definitive signal from extraterrestrial intelligence. He said: “If we don’t find ET, what we can say is that we established a new sensitivity level. If there were a signal above a certain power, we would have found it. Some of our conclusions are that the project didn’t completely work the way we thought it was going to. And we have a long list of things that we would have done differently and that future sky survey projects should do differently.”
Eric Korpela, astronomer and director of SETI@home, explained the challenge facing such searches: “There’s no way that you can do a full investigation of every possible signal that you detect, because doing that still requires a person and eyeballs. We have to do a better job of measuring what we’re excluding. Are we throwing out the baby with the bath water? I don’t think we know for most SETI searches, and that is really a lesson for SETI searches everywhere.”
To address this issue, Anderson and Korpela inserted about 3,000 artificial signals into their data pipeline before filtering out interference and noise. This allowed them to assess how sensitive their methods were.
Korpela described current assumptions in SETI research: “This powerful narrow-band beacon would be something that’s easy to detect. Then, once someone had detected that, they would dedicate more observing to try and find signals near it in frequency that might be lower power and wider band that contain information.” He added: “If we saw an extraterrestrial narrowband signal somewhere, we would probably have every telescope…pointing at that point on the sky…So far we haven’t had that.”
Reflecting on whether SETI@home was successful despite not finding evidence of extraterrestrial life, Anderson said: “I’d say it went way, way, way beyond our initial expectations…Our calculations were based on getting 50,000 volunteers. Pretty quickly, we had a million volunteers…and I would like to let that community and the world know that we actually did some science.”
The idea for SETI@home originated when Anderson was teaching at UC Berkeley—a university recognized as one of America’s top public research institutions with over 1,500 faculty members offering more than 300 degree programs through its various schools and colleges (official website). Former student David Gedye suggested using distributed computing—breaking up large problems so many smaller computers could work on them—to analyze astronomical data for signs of advanced civilizations.
SETI@home launched in 1999 with Anderson teaming up with Korpela and Dan Werthimer from UC Berkeley’s electrical engineering department. Within days they had over 200,000 users across more than 100 countries; within a year participation grew to two million.
The Arecibo telescope provided data passively as other astronomers used it for unrelated studies—a method called commensal observing—which enabled repeated coverage over much of the visible sky from Puerto Rico.
Korpela commented: “We are…the most sensitive narrow-band search of large portions of the sky…so yeah there’s a little disappointment that we didn’t see anything.”
Most current searches target specific stars rather than scanning broad areas as SETI@home did. Telescopes like Greenbank in West Virginia or MeerKAT in South Africa can only detect strong transmitters relatively nearby compared with Arecibo’s capabilities.
Anderson explained how processing worked: software developed by Korpela performed mathematical transformations on radio data while accounting for Doppler shifts caused by motion between Earth and potential sources—something made feasible by having access to millions of volunteer computers.
By around 2016 researchers realized they needed new strategies for analyzing accumulated detections; assistance came via supercomputing resources at Germany’s Max Planck Institute which helped reduce billions of initial detections down first to millions then hundreds requiring manual review.
Currently FAST is targeting each remaining candidate spot for about fifteen minutes per observation session; its collecting area is eight times larger than Arecibo’s former dish which collapsed during a storm in 2020.
Looking ahead at similar crowd-sourced projects today Korpela said: “I think it still captures people’s imagination to look for extraterrestrial intelligence…The biggest issue with such a project is personnel means salaries—it’s not the cheapest way…” He remains interested in reanalyzing all existing data if funding allows since advances since 1999 may reveal missed opportunities.
UC Berkeley continues its role as an innovative research institution focused on interdisciplinary collaboration (official website), supporting both academic pursuits through extensive library collections (official website) and ongoing scientific exploration.
