Extraterrestrial intelligence: the debate continues. A biologist looks at the numbers
DOI: 10.1063/1.2914965
In the Guest Comment in April (page 9), Frank Tipler argues that if extraterrestrial beings existed, our galaxy would be so full of their Von Neumann machine proxies that we could not have missed them. Tipler replaces Michael Hart’s and James Trefil’s humanoid colonizers with machines, to circumvent the costs of humanoid support and humanoid fragility. Francis Crick and Leslie Orgel replace them with cargoes of microorganisms in a revival of Svante Arrhenius’ century‐old “Panspermia” hypothesis.
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More about the authors
Leonard Ornstein, City University of New York, New York City.
