Photo: Bob O'Connor

Night watch: The new telescope at Oak Ridge Observatory, in Harvard, Mass., waits patiently for nanosecond light pulses that a distant civilization might be sending our way.

It doesn’t look like much: just a clapboard shed in a clearing, surrounded by tall pines. No plaque or other marking announces what goes on here. Inside stands a 4-meter-tall black metal frame covered in Mylar, looking sort of like a giant’s box kite ­waiting for a stiff breeze. Beneath the shroud of plastic are a largish mirrored disk, a second smaller mirror, and some cables and electronics.

Suddenly, the roof begins to glide backward on steel tracks, revealing the night sky overhead. Even as the contraption tilts slowly into place, its exact angle controlled by a computer in the next room, the true purpose of this unassuming apparatus might be unclear to the casual observer. But it constitutes the most sophisticated implementation of a concept that a few technologists, including me, have been pushing for more than four decades—a telescope dedicated to answering an age-old question: Is anybody out there?

With the unveiling last April of this new facility, the search for extraterrestrial intelligence, or SETI, entered a new era. Most previous SETI attempts have listened for radio ­signals, but after more than 40 years, none has detected anything of significance. This telescope—designed by Harvard University physics professor Paul Horowitz and his colleagues and constructed at the Oak Ridge Observatory, in Harvard, Mass., about 50 kilometers northwest of Boston—takes a new tack [see photo, “Night Watch”].

Horowitz is hunting for the briefest pulses of visible light that a far-off civilization could be sending toward Earth. His is the first telescope to be specially designed and dedicated to this purpose, and, many experts now agree, it represents the right direction for SETI to take. If E.T. is trying to talk to us, he’s probably beaming light our way, not radio waves.

It’s been said that the most important event in human history will be when someone discovers that we earthlings are not alone in the universe, that there are other beings smart enough to let us know they exist. For most of our history, the technology to look for extraterrestrial life was beyond our means. But the relatively recent advent of large dish antennas and extremely sensitive receivers gave us the tools to listen for radio frequency signals.

Starting in 1960, radio astronomers have mounted dozens of SETI experiments, some lasting only a few weeks or months, others running for years. Most of these searches were targeted at nearby star systems, those thought most likely to harbor life, while others encompassed the entire sky.

The two longest-running SETI projects to date, Phoenix and Serendip, both rely on the 305-meter-diameter Arecibo Radio Telescope, in Puerto Rico. Project Phoenix collects broadband RF signals from the antenna, which computers then digitize and split into narrow frequency channels, measuring the strength in each. Anomalous results—anything that rises above the noise—are compared with a comprehensive database of terrestrial radio sources. If the transmission can’t be identified, it is then checked against data from other radio telescopes to see whether it truly comes from the target star system.

Project Serendip, meanwhile, is tuned in only to 1420 megahertz, the frequency of the neutral hydrogen atom, which is the most abundant substance in the universe and can be readily detected, even by small telescopes.

But neither Phoenix nor Serendip, nor any other search, has turned up signals of extraterrestrial origin.

One reason for that failure is the sheer complexity of the task. Our galaxy contains more than a hundred billion stars, spread across an expanse of almost 100 000 light-years. The recent discoveries of extrasolar planets—which number more than 200 at last count—boost hopes that there is intelligent life out there. And yet, as astrophysicist and SETI pioneer Frank Drake famously postulated in equation form [see sidebar, “The Drake Equation ”], the likelihood that any one of those billions of star systems hosts not only a habitable planet but also one that has evolved beings who are both willing and able to communicate with us is quite low.

Low, but not zero. If you assume, for example, that one in a million stars has a planet bearing intelligent life, that means our galaxy is home to at least 100 000 advanced civilizations. Even if only one in a hundred million stars qualifies, that still leaves more than 1000 civilizations that could be trying to contact us.

To date, though, radio astronomers have heard nothing. It’s too soon to conclude that nobody’s out there: maybe SETI researchers are just looking in the wrong place or in the wrong way. I believe they’ve made the latter mistake. No intelligent society would attempt to communicate with us over hundreds of light-years using radio waves when physics suggests other wavelengths would be the more intelligent choice.