Professor of Physics Paul Horowitz's laboratory recently installed the experiment at the Harvard-Smithsonian Oak Ridge Observatory in Harvard, Mass. The optical SETI (or OSETI) experiment has occasionally registered a signal similar to what one would expect if another civilization's laser were aimed at us.

None of those signals has shown the regular repetitions that could indicate an intelligent hand behind them; but then, the researchers have just begun looking. Though such searches for laser lights from beyond our solar system have been done before, in an isolated and sporadic way, the Harvard experiment is the first broad-based and systematic search.

Horowitz has had his ears to the skies for interstellar radio messages for the past 20 years. He directs Harvard's BETA project, which for the past three years has searched 600 million channels for radio signals broadcast by an intelligent civilization. Before BETA there was META, an 8.4 million-channel searching device that went on-line in 1985 and was supported in part by funds from E.T. director Steven Spielberg.

While BETA continues its radio-wave search in full force, collecting the equivalent of a compact disc's worth of data every two seconds, none of the radio signals collected has yet been shown to be of intelligent origin. "After 20 years, maybe it's time to try something else," Horowitz says.

The idea of analyzing light flashes from distant parts of the galaxy is not a new one, Horowitz explains. Charles Townes, who shared the Nobel Prize in Physics in 1964 for his work on masers and lasers, first raised the idea in a paper co-authored with R.N. Schwartz, "Interstellar and Interplanetary Communication by Optical Masers," that was published in the journal Nature in April 1961. But technology developed just within the past five years finally made it a viable project. "This is very much an experiment of the '90s," Horowitz says.

The beauty of the new experiment, Horowitz explains, is that flashes of concentrated light are easy to detect and show up as distinct from other sources of illumination. If, for instance, Earthlings aim a high-intensity pulsed laser at a distant star, anyone watching from that star with a moderate-sized telescope will suddenly see a flash 1,000 times brighter than the light of our Sun -- "an efficient interstellar beacon."

And since the brightness of starlight and laser light both decrease at the same rate, that particular high-intensity laser beam shot from Earth would always be 1,000 times brighter than the light from our Sun, no matter how far it travels.

Reversing the direction, any extraterrestrial flash pointed the way of Earth would be easily distinguishable from the light of a distant star. That could make pulsed light the preferred method for communicating across galactic distances instead of radio waves.

If you remember childhood games involving walkie-talkies and messages communicated by flashlight beams, you'll recall that flashlight beams were much more reliable than static-filled walkie-talkie transmissions, if not as dramatic.

Horowitz, who has long been an optimist regarding the idea of extraterrestrial civilizations, cautions, however, that, "Maybe they're using 'zeta rays' to communicate, and the problem is we haven't discovered zeta rays yet."

Still, the elegance and simplicity of the new laser-detection experiment is appealing. BETA took four years to build (at a cost of hundreds of thousands of dollars), involves enough high-end computer equipment to fill a large truck, and uses an 84-foot radio telescope.

The OSETI equipment, funded by the Planetary Society, the SETI Institute, and the Bosack-Kruger Charitable Foundation, was put together in three months by Horowitz and fellow researchers Jonathan Wolff, Chip Coldwell, and Costas Papaliolios at a cost of less than $10,000.

"It fit in the back seat of my Corolla," Horowitz says, describing the monitoring device as being as big as a box "for a large loaf of bread." It uses leftover light from a 61-inch telescope that already was engaged in a survey of 2,500 nearby solar-type stars, an experiment run by researchers Joe Caruso, David Latham, Robert Stefanik, and Joe Zajac.

The simplicity of the new OSETI equipment means the experiment could easily be duplicated elsewhere. Researchers at the University of California at Berkeley, who have done some preliminary looking, are setting up an optical SETI experiment along the same lines, and their experiment will be operational soon.

A more detailed description of Harvard's optical SETI experiment is available on-line, and contains a call for the SETI research community "to consider alternative OSETI strategies -- choice of wavelength, pulse widths and repetition rates, revisit times, etc. -- in an attempt to identify a particularly compelling a priori strategy, involving both sender and receiver, that could be the basis for major Earth-based OSETI receiving efforts in the near term."

Optical SETI is an added tool for searching the heavens that has emerged just as the more traditional searches of radio frequencies are getting tougher.

Darren Leigh, a recent Harvard Ph.D. in applied physics who oversees the BETA project, says that cellular phones in particular have made it harder to hear signals from outer space. As satellite transmissions increase, Leigh says, we are confronted by the possibility that our interest in talking with each other might mean less chance of hearing a call from extraterrestrials.

Horowitz is optimistic about the optical SETI project, but 20 years of waiting have made him cautious. "I'll be excited when we get results," he says.