Page Content (OCR)
276 If we would not do that, why would they? Bracewell doubted that an omnidirectional transmitter blindly radiating 1000 megawatts in no par- ticular direction could be justified and sustained for centuries on end.” These considerations may drive technological civilizations toward listen- ing but not transmitting. Extraterrestrials who maintain radio beacons may be a subset—possibly a very small one—of what might be a much larger number of technological societies. Technological civilizations might send beacon signals only after they have detected signs of intelligence, or at least of life. Shostak proposed that extraterrestrials might target their beacons on those remote planets whose atmospheres show signs of biological activity. That would drastically shrink the number of targets, but the search range would be limited to relatively nearby planets—and the beacons would have to be repeated for millions or even billions of years in the hope that a radio-competent society would emerge. Rubin’s List Alan Rubin suggested 10 possible motivations for a civilization to main- tain beacons: (1) to get a response by targeting signals to main-sequence stars that were known to have planets, particularly if there were signs of life and intelligence; (2) hubris—the sending society might view itself as the glory of the universe; (3) to impress themselves or rival groups with their power and status; (4) evangelism—to save the souls of intel- ligent beings throughout the Galaxy; (5) entertainment—extraterrestri- als afflicted with ennui might find it amusing to transmit signals the way bored ship passengers put messages in bottles and toss them into the sea; (6) commerce—entrepreneurial aliens may want to swap informa- tion, using what they learn to produce and sell novelty items; (7) altru- ism and paternalism—an ancient advanced society might feel obligated to help struggling newcomers; (8) paranoia—a fearful civilization may feel it necessary to broadcast threats to intimidate potential unwanted visitors; (9) reproduction—an alien species might broadcast informa- tion about its genotype with instructions for creating members of its own species; (10) pugnacity—an aggressive society might seek to instill fear or to provoke conflicts among rival groups of recipients.” We return to the issue of motivation. Why would other intelligences maintain beacons? Horowitz recognized that assuming the intentions of the transmitting civilization is skating on very thin ice. Brin added that the ale on 2. as classic SETI scenario ignores the many reasons why another civilization might think that sending out messages was unwise.” Before Contact