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Galactic civilizations - Population dynamics and interstellar diffusionA model is developed of the interstellar diffusion of galactic civilizations which takes into account the population dynamics of such civilizations. The problem is formulated in terms of potential theory, with a family of nonlinear partial differential and difference equations specifying population growth and diffusion for an organism with advantageous genes that undergoes random dispersal while increasing in population locally, and a population at zero population growth. In the case of nonlinear diffusion with growth and saturation, it is found that the colonization wavefront from the nearest independently arisen galactic civilization can have reached the earth only if its lifetime exceeds 2.6 million years, or 20 million years if discretization can be neglected. For zero population growth, the corresponding lifetime is 13 billion years. It is concluded that the earth is uncolonized not because interstellar spacefaring civilizations are rare, but because there are too many worlds to be colonized in the plausible colonization lifetime of nearby civilizations, and that there exist no very old galactic civilizations with a consistent policy of the conquest of inhabited worlds.
Document ID
19810061288
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
Authors
Newman, W. I.
(Institute for Advanced Study Princeton, NJ, United States)
Sagan, C.
(Cornell University Ithaca, NY, United States)
Date Acquired
August 11, 2013
Publication Date
June 1, 1981
Publication Information
Publication: Icarus
Volume: 46
Subject Category
Space Sciences (General)
Accession Number
81A45692
Funding Number(s)
CONTRACT_GRANT: NSF AST-75-21153
CONTRACT_GRANT: NSF PHY-77-20612
CONTRACT_GRANT: NGR-33-010-101
Distribution Limits
Public
Copyright
Other

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