SETI Conference: Planning for a Long, Long Search
Think again. At an August 2004 symposium organized by The Planetary Society, leading SETI experts stressed that we've barely scratched the surface. Guillermo Lemarchand (University of Buenos Aires) put a number on our ignorance about alien signals. Several decades of radio searches, he described, have probed only a hundred-trillionth (0.00000000000001) of the "cosmic haystack" the radio channels, sky directions, and other parameters that need to be searched for the "needle" of an artificial signal.
But Murray repeatedly pressed the panel for specifics of what has been ruled out. Frank Drake, senior scientist at the SETI Institute, responded that no alien civilization appears to be continuously broadcasting a powerful "beacon" signal from a planet circling any of the nearest 1,000 or so Sunlike stars, at least in the frequency bands we've searched. If there were such powerful beacons, they'd have been picked up by Project Phoenix, an ambitious nine-year undertaking that the SETI Institute concluded in March 2004. (The SETI Institute's next big project, the Allen Telescope Array, is now under construction.)
So how would an eager-to-talk civilization try to catch attention? One option would be to target promising stars if not the whole Milky Way with narrowband radio blasts. In that case, our task is to turn a radio ear toward as many stars as possible for as long as possible, listening at as many channels as possible simultaneously. Drake thinks that searching vast numbers of stars for very powerful transmitters, by wide-field sweeping, is a better bet than scrutinizing nearby stars for weaker transmitters by sensitive searches that are narrowly targeted.
Despite the lack of results so far, there's a lot of excitement in the SETI community because search capabilities are increasing by leaps and bounds. SETI capabilities are growing at about the rate of "Moore's Law," which says the amount of computing power you get per dollar doubles every 18 months. Seth Shostak, senior astronomer at the SETI Institute, recently said that if Moore's Law continues to hold true, he thinks that we'll detect an alien communique within the next two decades.
But the workshop participants were less optimistic. "Maybe within 100 or 200 years," suggested Kent Cullers, the Institute's head of research and development. "Twenty years is too soon."
"I agree," put in Werthimer. "I think maybe 50 or 100 years."
Not all SETI efforts are radio-based. Paul Horowitz and Andrew Howard of Harvard have built a 72-inch telescope west of Boston to conduct a wide-sky survey for very brief pulses of light that might be directed Earth's way. The most powerful lasers designed so far (such as the Laser Megajoule in France and the National Ignition Facility in the U.S.) can blast out nearly a million billion watts of light for a few billionths of a second. In that brief instant such a laser, aimed at our solar system through a 10-meter telescope on a distant planet, would far outshine the planet's host star. Detecting such brief pulses of light is technologically easy. The ability to do it will soon be built into high-end amateur CCD cameras.
"If they really want to contact us, they can," Horowitz said.
But, the conference participants stressed, we still don't know if we're watching or listening the right way. For instance, between radio and visible light there's a gigantic unexplored spectrum of infrared and millimeter-waves frequencies. There's reason to think these are the most efficient frequencies for interstellar communication. Perhaps the aliens have decided that anyone smart enough to be interesting will realize this, and are signaling there accordingly. But we can't search these frequencies well until we do can SETI from above Earth's atmosphere.
"Your best guess is your worst enemy," admitted Werthimer. "It's naïve to think that the searches we're doing today are the best ones." Instead, he advises, think serendipity. "We should all be looking for little glitches in our data."