No. 21: May-Jun 1982
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 have 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 are soft tissues that are rarely preserved or perhaps because many eyes were jettisoned because the organisms didn't need them, as cave dwellers are wont to do with surprising rapidity.
Some of the letters responding to Tipler questioned whether an intelligent civilization would be stupid enough to build self-reproducing von Neumann machines for galactic exploration. Wouldn't it be far more fun to go in person rather than by proxy? And, some pointed out, von Neumann machines would be ravenous consumers of energy and materials and might turn on man as an unnecessary competitor. Machines are not immutable. Space radiation and other environmental factors might alter computer programs and memories to drastically affect the behavior and objectives of such machines. Actually, as one letter writer observed, the earth has already been invaded by a self-reproducing, energy-hungry machine with exploratory tendencies -- man!
(Anonymous; "Extraterrestrial Intelligence: The Debate Continues," Physics Today, 35:26, March 1982. Also: Ornstein, Leonard; "A Biologist Looks at the Numbers," Physics Today, 35:27, March 1982.)