Q. In searching for extra-terrestrial life, should we be sending light into space and looking for those same transmissions coming back, instead of listening for radio or electric signals?

H.K.

Chelsea

A. As a matter of fact, scientists started looking for bursts of laser light from out there just last October. And they're looking for signals from far away from a spot pretty close by, at the 61-inch optical telescope in Harvard, Mass.

Physicist Paul Horowitz is the principal investigator. For years he's run a search for extra terrestrial intelligence, one of several such SETI projects, listening for radio signals from outer space. The thinking is that any intelligent life that wants everybody to know they are out there would use radio waves to make themselves known, because they spread across the universe in all directions.

But American physicist Charles Townes, who shared the 1964 Nobel Prize in Physics for discoveries that led to the laser, has persuaded SETI scientists to use light as well, by showing them how bright it can be. A laser at the US Department of Energy's Lawrence Livermore Lab at Los Alamos can put out a nanosecond (one billionth of a second) burst that outshines our sun by 3,000 times.

If we have something like that, Townes reasons, civilizations on planets that are billions of years older than ours, which would presumably be more advanced, would have even more powerful light sources. Since light energy isn't absorbed by interstellar gas and dust the way radio waves are, Townes and the SETI folks reason that advanced civilizations might use light instead of radio waves to advertise their existence. And those civilizations might be advanced enough to know which planets in other galaxies have conditions that are right to support life, and could precisely aim their narrow beams of light at whomever they want to contact.

So Horowitz built a device to look for E.T.'s lasers. Since October, it has detected three dozen events whose electrical signatures are the same as a flash of light.

Is that a sign of extraterrestrial intelligence? Astronomer Robert Stefanik, who runs the observatory doing the work, says, ``We don't know of any natural phenomenon that creates pulses like this.''

Horowitz is skeptical, saying ``they're probably just artifacts of the detector, radioactive decay particles or something like that.''

They have trained the telescope back at the same spots but did not see a second signal, which might indicate a pattern and intelligent life.

The search for extraterrestrial intelligence continues. And now we're not just listening. We're looking, too.