IN THE Cascade mountains of California, north of Lassen Peak, astronomers are looking for aliens. The Allen Telescope Array (mostly paid for by Paul Allen, co-founder of Microsoft) consists of 42 dish antennas, each six metres across, scattered across the countryside. When the array is complete, it will have 350 dishes that, by acting in concert, will have the power of a single instrument 700 metres across. The Allen telescope is looking for aliens the traditional way: by searching for radio signals that have either been sent out deliberately, or leaked into space accidentally, as human radio signals are. The search for extraterrestrial intelligence, or SETI, is a 50-year-old idea. Much progress has been made in locating Earthlike planets (see article) but about 1,000 star systems have also been subject to serious radio scrutiny. The Allen array will increase the number to 1m within a decade.
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