Watching for a Signal from E.T.

By Frederic Golden

Forget that dramatic moment in the film Contact when the radio astronomer played by Jodie Foster rips off her earphones in astonishment after hearing four telltale beeps. Pure fiction, say scientists--and not only because of her hokey headset. When extraterrestrials finally make themselves known, they may not use radio at all. Instead, they're just as apt to signal us with beams of light. Says physicist Freeman Dyson of the Institute for Advanced Study in Princeton, N.J.: "It's foolish to try to guess what an extraterrestrial civilization might use. You ought to try all available technologies to detect it."

Increasingly that means looking as well as listening. For nearly four decades, SETI (search for extraterrestrial intelligence) scientists have scoured the skies with their big radio antennas without getting so much as a convincing peep, though there have been some tantalizing false alarms. Not only can suspect signals be elusively faint, they are also hard to separate from the universe's hodgepodge of natural noises. Given that, many scientists have begun wondering about entirely different kinds of extraterrestrial smoke signals, especially lasers. Says Harvard physicist Paul Horowitz, a veteran of many SETI radio searches: "Lasers are an interesting alternative."

Interesting enough for him to kick off his own O(for optical)SETI effort. Needing just three months and $20,000, his team built a stereo-size detector designed to look over the shoulder of Harvard's 61-in. telescope as it conducts regular studies of starlight. While stars typically pulsate comparatively slowly, Horowitz's device is calibrated to spot intense stellar flare-ups lasting only a few billionths of a second. Such "events," he figures, would probably be powerful bursts of artificial light aimed at us from an inhabited planet orbiting that star. In short, an interstellar hello.

At least that's the theory. Since the apparatus went online last October, it has studied some 2,000 sunlike stars, but detected only a few anomalous flashes--probably from high-energy particles that regularly shower the earth. "We're still investigating," Horowitz says.

So too are a number of other teams in what is starting to look like OSETI mania. At Princeton, physicist David T. Wilkinson will soon begin surveying nearby stars with a detector similar to Horowitz's. At the University of California, Berkeley, extrasolar-planet hunter Geoff Marcy is re-examining his data for sharp spectral lines that might indicate a continuous beam of light intended as a low-power signal. Another Berkeley team, led by SETI veteran Dan Werthimer, is looking for short, powerful laser bursts in a series of automated observations of 2,500 nearby stars. Later he plans to turn to invisible infrared light and other galaxies.

Could aliens actually send a flash across our Milky Way galaxy? Without a doubt, says Nobel laureate Charles Townes, who first suggested lasers as a tool for interstellar communication nearly 40 years ago. Adds Werthimer: "They may have stuff out there we couldn't even dream of." O.K., E.T., never mind the phone call. Start blinking.