LOS ANGELES — Not content to just listen for aliens, a group of California scientists has begun looking for them, too.
For years, the search for extraterrestrial intelligence — commonly known as SETI — has focused on sifting through the radio or microwave transmissions that stream toward Earth from all quarters of the universe. By crunching the data, scientists hope to detect signals generated by alien civilizations.
Now, scientists at the SETI Institute, the University of California's Berkeley and Santa Cruz campuses and the Lick Observatory have expanded their search to include a hunt for fleeting flashes of laser light. Using a 40-inch telescope at Lick, they are hunting for pulses as brief as one-billionth of a second that emanate from star systems hundreds of light-years away.
"It's a very long shot, but it's very inexpensive to do," said Frank Drake, the SETI Institute's board chairman.
The optical hunt requires use of an existing telescope and about $10,000 worth of equipment. In contrast, the group is building a $26 million array to enhance its search for radio signals.
If the optical project does detect a pulse, it's not clear what meaningful two-way communication could ensue. Laser pulses, traveling at the speed of light, can take hundreds if not thousands of years to travel between the stars.
"If you do get in touch, the conversation is going to be tedious," said Seth Shostak, a SETI Institute astronomer.
The idea of hunting for alien laser pulses has been around for 40 years, or nearly as long as the laser itself. In the United States, teams based at Harvard University, Princeton University, Berkeley and in Columbus, Ohio, are conducting optical searches.
Unlike radio-focused efforts, a successful optical hunt would require catching an alien civilization deliberately targeting Earth with a laser beacon or pulse.
If radio SETI is listening for a shout from an individual in a crowd, its optical counterpart is looking for a subtle wink.
"With radio, generally speaking, signals tend to spread out more — you don't have to target your receiver. With optical receivers, you have to know where the guy is on the other end," Shostak said.
The system installed at the Lick observatory uses three light detectors, called photomultipliers, hooked up to its Nickel Telescope.
The telescope is pointed at each candidate star for 10 minutes. The light it gathers is then split and shuttled to each detector. While light from the star itself can also trigger the detectors, the number of photons, or light particles, from a laser pulse would outnumber them 1,000-to-1, Drake said.
So far, the search has examined about 300 stars, as well as a few star clusters. No alien laser pulses have been detected, but the hunt will continue for at least the next year, hitting 1,000 stars.
On the Net: SETI Institute: www.seti.org