Instead of listening for extraterrestrial intelligence, scientists are now looking for it. Indeed, a group of California astronomers has designed special equipment to look for powerful light pulses reaching Earth from other star systems. "This is perhaps the most sensitive optical SETI [search for extraterrestrial intelligence] search yet undertaken," says Frank Drake, chairman of the board of the SETI Institute and co-investigator on the project. "We are looking for very brief but powerful pulses of laser light from other planetary systems, rather than the steady whine of a radio transmitter."

Drake started the modern hunt for alien intelligence in the 1960s by launching radio SETI, which uses large antennas and multimillion-channel receivers to scan the sky for narrow-band signals, the signature of a purposely built transmitter, according to the SETI Institute. Scientists tried an optical SETI before, but the effort was prone to frequent false alarms from sources as varied as muon showers and radioactive decay within the sensors themselves. They expect the new system, though, to cut down the number of false alarms to approximately one per year, thanks to the short time frameone billionth of a secondin which photons must simultaneously hit all three detectors in the equipment.

The team has outfitted the 40-inch Nickel Telescope at the University of Californias Lick Observatory (see image) with three photomultiplier tubes and software designed to allow the setup to run automatically. The system is able to detect optical beacons hundreds of light-years away. So far the astronomers have examined hundreds of individual star systems, as well as some star clusters. They plan to continue their search on a weekly basis throughout the next year.

There's one caveat concerning optical SETI, as compared with its radio counterpart: for us to find extraterrestrial civilizations, they must be deliberately signaling to us in precisely our direction.