Intergalactically Speaking; July 2000; Scientific American Magazine; by Swenson, Jr.; 3 Page(s)

Among our galaxy's 100 billion or more stars there may be thousands of advanced civilizations, some scientists suspect-a possibility supported by recent evidence indicating that planetary systems are more common in the Milky Way than was previously thought. For four decades, researchers have sporadically scanned the heavens for any radio signals that an advanced civilization may have emitted into the vastness of the galaxy. This search for extraterrestrial intelligence (SETI) is a passive pursuit, based on the use of dish antennas and sensitive radio receivers to pull in signals that, if they are out there, are probably quite weak by the time they get to us.

Essentially all major SETI programs here on Earth have been based on attempts to receive signals that would have been transmitted decades or, in all probability, centuries or millennia ago. For this reason, little has been published on the complementary problem of SETI, which could be phrased as follows: What would it take to build a radio-transmitting system that would have even the slightest chance of being detected by a receiver tens or hundreds of light-years away?