Page Content (OCR)
275 We are looking for a beacon signal deliberately designed to attract the attention of any interstellar listeners. Finding the subtle variations of any message will demand far more sensitive instruments.” SETI focuses on beacons because that is what our current technological capabilities allow us to do. Horowitz optimized his own searches for pure narrow-band carriers because they are easier to detect, stand out clearly as artificial, are efficient beacons, and can be distinguished from terrestrial interference. However, there is a fundamental problem: The best beacon is the worst message, and the best carrier of information is the worst beacon.” How likely are beacons? The authors of the Project Cyclops report thought that the first civilizations to undertake the search undoubtedly followed their listening phase with long transmission epochs (emphasis added). “Their perseverance,” the report went on, “will be our greatest asset in our beginning listening phase.” Here again, we are assuming the behavior of alien civilizations. The NASA targeted search assumed that there are at least 100,000 beacons in the Galaxy, so that one will be found in the nearest million stars. If there are between 1 and 100,000 beacons in the Galaxy (and if they are using continuous wave transmission), a sky survey is the best strategy. For the sky survey to be useful, the beacon must be on almost constantly and for long periods of time.” A Mirror Image. In order for an extraterrestrial civilization to detect our transmissions, explained Jill Tarter, their instruments must be looking in our direction at the time our signal arrives—and they must have chosen the right instrument. The chances of that happening are zero, unless we commit to transmitting for a long time.” The underlying issue is the motivation for operating beacons. Drake assumed altruism: “Other civilizations may well generate signals intended to benefit others, signals that are strong enough only for the deserving to receive.” Oliver thought that beacons might exist to help young races such as ours o join the galactic community. If we come into contact with a network of civilizations, the first requirement imposed on us might be to erect a beacon to continue that process.” Davies was skeptical about the assumption that the aliens are doing the ransmitting. The enormous asymmetry of effort between the transmitting and receiving ends of the operation means that one has to suspend the Copernican principle (that we are typical) to justify SETI. We have to assume that they are prepared to act in a superhuman way by spending arge sums of money over eons of time sending signals in all directions with ittle hope of a reply. There Will Be Lighthouses in the Cosmic Night