optical_setisearch_000503 It may seem fantastic to assume that advanced alien civilizations are beaming signals across the cosmos, but the possibility has intrigued respected astronomers enough that several have taken up the task of finding those messages.
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Harvard University, Princeton University and the University of California at Berkeley have each developed programs to find a specific kind of signal -- lasers -- penetrating our atmosphere, from extraterrestrials attempting to communicate with humanity.
That three prestigious institutions are involved in this search is testament to the perception of SETI -- the search for extraterrestrial intelligence -- in the scientific community. While SETI opponents say that technologically advanced life is extremely rare in the universe, there is also a popular belief that there are simply too many stars and planets for life to be limited to one planet, Earth. A search, therefore, would be justified.
Optical SETI is a particular branch of the search that involves setting up ground-based telescopes to look for laser signals hitting our planet. The telescopes are set up to look for a continuous, powerful beam or a laser that pulses every billionth of a second.
"Lasers have the advantage that they can send a lot of information. You could send your whole Library of Congress, all your music, poetry, literature, science, medicine."
The search for lasers is only one method in a broader SETI search. Early searches, dating back 40 years, involved scanning the sky for radio signals. Those kind of searches continue to this day, involving some of the world's most powerful radio telescopes.
Radio signals carry less information than laser signals, but searching for them takes advantage of the possibility that even if there has been no attempt by aliens to communicate with us, advanced civilizations might inadvertently broadcast radio signals during the course of their own intraplanetary communication.
The idea is based on the fact that signals from television and radio shows on Earth are traveling at the speed out light through the galaxy; those involved in the radio search hope that earthbound radio telescopes could pick up similar signal leakage from aliens.
Why would aliens, if they exist, send laser signals? For one, lasers can carry immense amounts of information, meaning that aliens interested in communicating with other advanced civilizations might build lasers for the task. Powerful lasers can also be transmitted with relatively inexpensive equipment and can travel from one planet to another -- across the galaxy -- without much interference.
"Lasers have the advantage that they can send a lot of information," said Berkeley researcher Dan Werthimer, who heads up Berkeley's alien-search effort. "You could send your whole Library of Congress, all your music, poetry, literature, science, medicine."
Harvard's 61-inch (1.5-meter) optical telescope
Assuming that one other advanced civilization exists, astronomers say, then the likelihood that there are many, many more is quite high. Given a galaxy filled with advanced civilizations, aliens may be regularly communicating with each other via laser beams. They might also conduct searches for new civilizations that have not yet joined the intergalactic conversation.
All of this, the astronomers admit, sounds fantastical. "It's a longshot," said Prof. David T. Wilkinson of Princeton University, who leads an optical SETI team of students, faculty and community members. "My colleagues' eyebrows go up once in a while when I tell them what I'm doing these days, because I've done some pretty straightforward cosmology."
But Wilkinson has a simple answer for naysayers who ask: "Why in the world should we spend our time looking for laser signals from aliens?"
"Why not?" said Wilkinson, who estimates that there is a one-in-a-million chance of finding a laser signal from aliens. "It's cheap, and easy to do."
Wilkinson's project involves a small optical telescope that will search the sky in tandem with a similar telescope at Harvard University. If both telescopes find a particularly strong light signal, Wilkinson says, it would confirm that they have received an alien signal.
At Berkeley, two different optical SETI searches operate. One project searches for a continuous laser pulses from 1,000 stars. The second uses a 30-inch (0.8-meter) telescope at the Leuschner observatory to search for laser pulses. It has already searched 300 stars, but has so far turned up nothing.
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