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I Love Lucy and Laser Beams

All SETI researchers seek signals that couldn't be produced by natural phenomenon. Historically, the search has focused on radio signals confined to one or a few channels, like those broadcast by a radio station, which which would be unlikely to occur naturally–the processes that create natural radiation spread it out across tens to millions of frequencies. These "narrowband" radio signals are more likely to come from accidental or non-directional communications–for example, the broadcasts of our own I Love Lucy episodes that leaked into space 60 years ago, or radio broadcasts from the turn of the 20th century.



But even humans are moving beyond beaming such transmissions in all directions, at least when it comes to TV. And so some SETI researchers think such radio communications might be old-hat for advanced civilizations attempting to contact us, who are likely to be much more advanced. That's why some researchers search the heavens for laser-beam signals, which can efficiently transmit much more information from point to point than can radio waves.



"If you wanted to send the Encyclopedia Galactica across space, you'd do it with lasers, not radio waves," Stuart Kingsley says.



The downside is that laser communications are brief and must be precisely aimed at specific planetary systems (though it's conceivable that advanced civilizations could have invented things we can't even fathom, such as lasers that shoot in all directions). Searches for laser beams, or "optical SETI" programs, have grown in recent years, and Kingsley is part of the reason. A fiberoptics engineer by day, his passion for optical SETI led him to help lobby the field to adopt the approach in the 1990s.



Harvard astronomer Paul Horowitz leads one such optical SETI program, which uses an optical telescope in Boston with an array of 1024 tiny detectors, each capable of measuring and recording an interstellar laser beam. The telescope surveys 1 degree of sky at a time and takes about one year to cover the Northern sky. "We're looking for something that's aimed at us, and designed to create attention," he says. It could work: If humans shined our strongest laser at a nearby star in our galaxy, the laser light would appear 10,000 times brighter than the sun–albeit for several brief nanoseconds, Horowitz says. Aliens could conceivably send even stronger signals. Both Horowitz and Werthimer say they'd like to search for infrared lasers, which would be able to shine through interstellar dust clouds better than visible light. But this technology remains prohibitively expensive to monitor for now.