Seti@Home has clocked half-a-million years in computer time searching for ET on home PCs, but the real work isn't due to begin in earnest until January.
The Seti@Home project harnesses the spare computing cycles of millions of PCs across the globe to search for telltale signs of intelligent life in radio signals beamed from outer space.
Since its launch 18 months ago, 2.6 million people in 226 countries have downloaded Seti@Home's screensaver software, which scans radio data when their computers aren't otherwise in use.
The screensaver looks for strong signals among the white noise of the universe's background radio transmissions.
But the process of figuring out which signals, if any, have come from alien civilizations won't start operating at full swing until the end of January, when the project brings online all its back-end servers.
"We only recently started the back-end analysis," said David Anderson, Seti@Home's director. "We've been doing bits and pieces here and there. It will be turned on full blast next month."
In the meantime, the Seti@Home project has become the largest computing problem ever undertaken. It has clocked an astonishing 500,000 years in computing time, with another 1,000 years of processing time contributed every day.
Collectively, the 2.6 million Seti@Home machines are twice as powerful as the most powerful supercomputer on the planet, and a lot cheaper.
The U.S. Government's ASCI White, housed at a California nuclear weapons research lab, is rated at 12 Teraflops (trillion operations a second) and cost $110 million to build.
All day, every day, Seti@Home operates at around 25 Teraflops but cost only $500,000, excluding the cost of the home PCs.
"It's the biggest supercomputer on the planet by far," said the project's chief scientist, Dan Werthimer, an astronomer at the University of California at Berkeley's Space Sciences Laboratory.
To date, the Seti@Home screensavers have identified 500 million strong radio signals from data gathered by the Arecibo radio telescope in Puerto Rico, the world's largest radio telescope, which was built into a huge, bowl-shaped sink hole at the top of a mountain.
"In the screensaver, strong signals look like skyscrapers sticking up above the grass," said Werthimer.
Using a variety of algorithms, the screensavers have whittled down the 500 million strong signals, or spikes, to about 125 million that look interesting.
All of these 125 million signals display a Gaussian, or bell curve, profile. As the Aricebo telescope scans across the sky, the signal becomes progressively stronger and then weaker, just like a bell-shaped curve.
A signal displaying a Gaussian profile is less likely to be noise from terrestrial cell phones, airplanes or satellites, and probably originated from a single point in space – maybe a planet orbiting a nearby star.
"That characteristic pattern gets us excited," said Werthimer.
But to ensure the signal came from an alien civilization, it must be transmitted from the same part of the sky, at the same frequency, on two or more observations, which would indicate a persistent signal and not just a random burst of energy.
This "back-end" analysis was only recently begun, but already it has identified hundreds of signals that have been broadcast twice, three times, even four times, over an 18-month period. A map on the project's site shows the results: Red dots are signals picked up more twice. Green dots are signals detected four or more times.
But so far, every signal that merits closer inspection has proven a red herring.
"Occasionally you find very strong signals and you look more closely but it turns out to be a satellite or interference," said Werthimer.
Even though 500,000 years of computing time seems like a lot of time to throw at a problem, Werthimer said it's just the beginning.
"I've been doing this for 25 years and I still think we're just scratching the surface," Werthimer said. "We've got a long way to go. We're searching such a small range of frequencies, it may take another 50 or 100 years."
Seti@Home currently searches a narrow 2.5 Mhz band among the billions of potential radio bands. A thorough search for signs of intelligent life would include a much wider swath of the electromagnetic spectrum.
A good candidate would be light. Advanced alien civilizations might communicate with lasers because of their high information bearing capacity.
Another Seti program at Berkeley plans to start searching for patterns in light. But unlike radio, light has trouble penetrating the huge clouds of cosmic dust that are spread throughout the universe.
There is also the problem of ever-increasing amounts of radio pollution. The Earth is already brighter than the Sun in terms of radio radiation – all of it man-made.
"It's getting harder to do Seti on this planet," said Werthimer. "We may have to go to the back side of the moon."
The good news, Werthimer said, is that the ever-increasing power of computers means that more and more cycles can be applied at the search.
Already Seti@Home has added the ability to find pulsed, and not just steady, signals, and will shortly include data from the Southern Hemisphere.
Werthimer said Seti's search capabilities have increased by a factor of one million in the last 20 years, but it will take a one billion-fold increase before a comprehensive search of the universe can be done.
"We are 20 or 30 years away from a thorough search," he said. "It's like combing a cosmic haystack. We've just started poking around the edges."
"Even though I think the universe is teeming with life, I think it's going to be a while. But it will probably be in our lifetime."
Seti@Home's director, Anderson, added: "Detecting an alien signal would probably be one of the most exciting events in human history, if not the most exciting.
"It would change all of our lives forever. The probability of it happening is not exceptionally high but it's like the lottery. The payoff is so big, it's worth doing anyway."
