Frank Drake spent many blissful hours as a boy musing about the possibility of intelligent beings out there amid the stars, but he was reluctant to bring the subject up with his parents or teachers because it seemed so far-fetched. The idea nagged at him when he completed his graduate studies in astronomy at Harvard University in 1958 and when he took a job at the newly founded National Radio Astronomy Observatory in Green Bank, West Virginia. If there are other technologically advanced societies in our galaxy, he theorized, they might be using means of communication similar to our own. So in the spring of 1960, he pointed Green Bank's 85-foot antenna toward nearby stars Tau Ceti and Epsilon Eridani, making the first attempt to eavesdrop on radio broadcasts from extraterrestrial civilizations.
The two-month listening program, dubbed Project Ozma, did not turn up any signs of intelligent life, but it did generate a lot of excitement among astronomers by demonstrating that humans had the means to receive signals from hundreds of trillions of miles away. A year later Drake invited a dozen astronomers, engineers, and biologists to Green Bank to try to quantify the likelihood that anybody out there in the Milky Way was transmitting. "It was a very exciting few days for everyone," Drake recalls. "For the first time they were able to discuss a subject that had fascinated them but which until then had seemed completely out of reach."
This month the SETI (Search for Extraterrestrial Intelligence) Institute, which Drake codirects, will begin a round-the-clock search for radio signals in our galaxy with the newly constructed Allen Telescope Array in the Cascade Mountains in Northern California. Underwritten by a $26 million donation by Microsoft cofounder Paul Allen, the array currently consists of 42 dishes, each 20 feet in diameter, which can be used to listen for signals from several stars in many different radio bands simultaneously.
The odds that the array will turn up any signs of intelligent life are expressed by a formula Drake developed to help focus the discussion at the Green Bank conference 45 years ago. Astronomers refer to it simply—and reverentially—as the Drake Equation:
