... Science Frontiers ONLINE No. 21: May-Jun 1982 Issue Contents Other pages Home Page Science Frontiers Online All Issues This Issue Sourcebook Project Sourcebook Subjects Don't build von neumann machines Back in April 1981, Frank J. Tipler published a comment in Physics Today entitled, "Extraterrestrial Beings Do Not Exist." A key element of his argument was that the first intelligent civilization would inevitably colonize the entire universe with themselves or their self-reproducing (von Neumann) machines. Since we can detect neither kind of colonist ... we must be the first and only intelligent civilization. Essentially Tipler was criticizing the prevailing notion that, from a statistical point of view, there must be many other civilizations among the numberless stars and galaxies. Tipler's thoughts evoked a richly provocative group of letters, some of which were published in the March 1982 issue of Physics Today along with a closely related article by Ornstein. Ornstein tackled the problem of estimating the probability that intelligent life would evolve on other planets from a biologist's perspective. Whereas some physical scientists ... set this probability at about 1.0 , Ornstein inclines toward 10-9 , believing that intelligent life is probably unique to the earth. But concludes Ornstein, the 15 separate developments of eyes among disparate terrestrial organisms may infer some unrecognized directing factor in evolution that would force him to revise his estimate upwards drastically. On the other hand, those 15 eyes might indicate a common, but still undiscovered, eye-possessing ancestor far back along evolution's track. The fossil record might be mute on this matter because eyes ...