in Natural History (Mar. 1979), P.O. Box 6000, Des Moines, Iowa 50340.
If civilized societies, populated creatures similar to humans, inhabit any of the 2.5 billion planets in the Milky Way now presumed capable of supporting life, it. is not likely that even one of them has achieved the level of technological expertise to broadcast word of its existence to Earth.
Wesson, a political scientist at the University of California, Santa Barbara, speculates that any major civilizations on other planets...