The vast SETI@home network of volunteers is, in effect, one of the world's most powerful supercomputers (averaging 480 teraFLOP per second as of November 2008). In fact, for a long time it was overpowered. In the first six years the Berkeley lab never managed to put all the volunteers to full use. For instance, by April 2005, the lab had "split" (created) 228 million work units from its data tapes laboriously recorded at Arecibo. But it had sent out 1,618 million work units to meet the volunteers' demand. The difference was made up by sending out duplicates. Lots of duplicates.

Having each work unit processed by at least two (or three) people independently provides an essential check for eliminating bad results, such as occasionally come from malicious hackers or from users overclocking their computers (setting a computer chip to run at a faster megahertz speed than it is rated for, which can cause it to miscompute). But bad results are rare, so processing a work unit more than three times serves no purpose.

In 2005, however, this embarrassing waste of computing power (and electricity!) was remedied.

The software for volunteers was overhauled to create a system called BOINC, the Berkeley Open Infrastructure for Network Computing. This gives users the flexibility to divide their computer time between SETI@home and other distributed-computing projects, such as the 80 or so that are now (May 2009) under way in molecular biology, climate modeling, physics, and mathematics. According to the SETI@home website, "Each work unit is now processed a limited number of times. When we have no work for your computer, you'll get a 'no work available' message. We encourage you to participate in other BOINC-based projects; then, when SETI@home has no work, your computer can stay busy doing other scientific research." The transition from "SETI@home Classic" to SETI@home/BOINC was completed in December 2005.

New SETI@home Directions

Meanwhile, the Berkeley team was working to expand SETI@home into other new realms:

1. The biggest change was inaugurated in the summer of 2006. SETI@home's old "line feed" antenna above the Arecibo dish was finally shut down, and the project instead began to record data from the five-times-more-sensitive ALFA multibeam receiver, which was installed at Arecibo in 2004. It looks at seven spots in the sky ("beams") at once instead of just one, so SETI@home now has seven recorders swallowing different data at once. And each records radio waves with two polarizations, not just one, making for 14 times as much data with 5 times the sensitivity.

In addition, the new SETI@home software, with which volunteers' computers analyze the new multibeam data, is itself five times as sensitive as the old. And the new receiver arrangement is more impervious to radio interference from Earth. More about the rejuvenated SETI@home appeared in a Planetary Society SETI Update.

One thing this means is that SETI@home now needs more volunteers. If you've waited because you don't want to waste your computer's time on unnecessary duplication, wait no more. Those days are over.

2. A separate, new branch of SETI@home is a project called AstroPulse: a different type of analysis to search existing SETI@home data for extremely brief, wideband radio pulses. This is something that's never been done well before. Astronomers think that such pulses could, theoretically, come from several possible sources: ETs trying to catch attention, exotic processes on neutron stars, and evaporating mini- black holes that might be left over from the Big Bang.

After years of preparation, AstroPulse finally went online in August 2008. SETI@home users automatically receive the AstroPulse analysis software, and the 8-megabyte work units that it dissects, without having to take special action. Your computer divides its time between AstroPulse and SETI@home proper.

In addition, the Berkeley SETI team is running a second radio pulse-search project, called Fly's Eye, using the Allen Telescope Array in California. While AstroPulse is very sensitive but sees only tiny bits of the sky at a time, Fly's Eye watches huge areas of the sky (100 square degrees at once, 3,000 times as much as AstroPulse sees), but at much lower sensitivity. So the two projects are complementary. Fly's Eye began in early 2008. Here is a detailed paper (November 2008) about both AstroPulse and Fly's Eye.

The SETI@home team has also looked into enlarging the search to the southern half of the celestial sphere — important sky territory that Arecibo cannot see. This project would piggyback on the 64-meter Parkes radio telescope in Australia, which is already hosting the Southern SERENDIP program (described below). It too has a multi-beam receiver.

"All of this is funding-contingent," Werthimer warns. SETI@home is continually seeking donations (tax-deductible) so it can continue with its plans.

In May 2009, SETI@home celebrated its 10th anniversary. The SETI Institute and Planetary Society sent out a press release for the occasion, noting, among other things, that SETI@home is currently "funded by donations from volunteers. . . . But [Werthimer] and Anderson intend to keep it running as long as there is interest.

“ 'We’re in this for the long haul. We’re looking for a needle in a haystack. It could take a hundred years,' Werthimer said. 'As long as we have some way to increase the sensitivity of our radio detectors or the frequency range or the part of the sky we’re looking at, we’ll still be doing something worthwhile.' ”

Strengths: SETI@home is performing the deepest wide-sky survey of the 21-cm frequency that has ever been done, and that can be done with current equipment. It has grown as new technology comes available, has expanded public understanding of SETI issues, mobilized enthusiasts and made them aware of their numbers, and blazed the trail that other distributed-computing projects have followed.

Weaknesses: SETI@home is basically a 21-cm survey. If we haven't guessed right about the alien broadcasters' choice of hailing frequency, the project is barking up the wrong tree — in a forest of thousands of trees. Secondly, there has been little real-time followup of interesting signals. Lack of immediate, dedicated followup means that many scans are needed of each sky position — in order to deal with the problem of interstellar scintillation if nothing else.

With its first, single-feed receiver, SETI@home logged at least three scans of more than 67 percent of the sky observable from Arecibo, amounting to about 20 percent of the entire celestial sphere. Of this area, a large portion was swept six or more times. Werthimer says that a reasonable goal, given issues such as interstellar scintillation, is nine sweeps of most points on Arecibo's visible sky.

Continued; click "Next Page" below.