Book contents
- Frontmatter
- Contents
- Preface to the Second Edition
- Preface to the First Edition
- 1 An Explanation for the Absence of Extraterrestrials on Earth
- 2 One Attempt to Find Where They Are: NASA's High Resolution Microwave Survey
- 3 An Examination of Claims that Extraterrestrial Visitors to Earth Are Being Observed
- 4 The Likelihood of Interstellar Colonization, and the Absence of Its Evidence
- 5 Pre-emption of the Galaxy by the First Advanced Civilization
- 6 Stellar Evolution: Motivation for Mass Interstellar Migrations
- 7 Interstellar Propulsion Systems
- 8 Interstellar Travel: A Review
- 9 Settlements in Space, and Interstellar Travel
- 10 Terraforming
- 11 Estimates of Expansion Timescales
- 12 A Search for Tritium Sources in Our Solar System May Reveal the Presence of Space Probes from Other Stellar Systems
- 13 Primordial Organic Cosmochemistry
- 14 Chance and the Origin of Life
- 15 The RNA World: Life before DNA and Protein
- 16 The Search for Extraterrestrial Intelligence
- 17 Alone in a Crowded Universe
- 18 Possible Forms of Life in Environments Very Different from the Earth
- 19 Cosmological SETI Frequency Standards
- 20 Galactic Chemical Evolution: Implications for the Existence of Habitable Planets
- 21 The Frequency of Planetary Systems in the Galaxy
- 22 Atmospheric Evolution, the Drake Equation and DNA: Sparse Life in an Infinite Universe
- About the Editors and Contributors
- Author Index
- Subject Index
1 - An Explanation for the Absence of Extraterrestrials on Earth
Published online by Cambridge University Press: 20 October 2009
- Frontmatter
- Contents
- Preface to the Second Edition
- Preface to the First Edition
- 1 An Explanation for the Absence of Extraterrestrials on Earth
- 2 One Attempt to Find Where They Are: NASA's High Resolution Microwave Survey
- 3 An Examination of Claims that Extraterrestrial Visitors to Earth Are Being Observed
- 4 The Likelihood of Interstellar Colonization, and the Absence of Its Evidence
- 5 Pre-emption of the Galaxy by the First Advanced Civilization
- 6 Stellar Evolution: Motivation for Mass Interstellar Migrations
- 7 Interstellar Propulsion Systems
- 8 Interstellar Travel: A Review
- 9 Settlements in Space, and Interstellar Travel
- 10 Terraforming
- 11 Estimates of Expansion Timescales
- 12 A Search for Tritium Sources in Our Solar System May Reveal the Presence of Space Probes from Other Stellar Systems
- 13 Primordial Organic Cosmochemistry
- 14 Chance and the Origin of Life
- 15 The RNA World: Life before DNA and Protein
- 16 The Search for Extraterrestrial Intelligence
- 17 Alone in a Crowded Universe
- 18 Possible Forms of Life in Environments Very Different from the Earth
- 19 Cosmological SETI Frequency Standards
- 20 Galactic Chemical Evolution: Implications for the Existence of Habitable Planets
- 21 The Frequency of Planetary Systems in the Galaxy
- 22 Atmospheric Evolution, the Drake Equation and DNA: Sparse Life in an Infinite Universe
- About the Editors and Contributors
- Author Index
- Subject Index
Summary
Are there intelligent beings elsewhere in our Galaxy? This is the question which astronomers are most frequently asked by laymen. The question is not a foolish one; indeed, it is perhaps the most significant of all questions in astronomy. In investigating the problem, we must therefore do our best to include all relevant observational data.
Because of their training, most scientists have a tendency to disregard all information which is not the result of measurements. This is, in most matters, a sensible precaution against the intrusion of metaphysical arguments. In the present matter, however, that policy has caused many of us to disregard a clearly empirical fact of great importance, to wit: There are no intelligent beings from outer space on Earth now. (There may have been visitors in the past, but none of them have remained to settle or colonize here.) Since frequent reference will be made to the foregoing piece of data, in what follows we shall refer to it as ‘Fact A’.
Fact A, like all facts, requires an explanation. Once this is recognized, an argument is suggested which indicates an answer to our original question. If, the argument goes, there were intelligent beings elsewhere in our Galaxy, then they would eventually have achieved space travel, and would have explored and colonized the Galaxy, as we have explored and colonized the Earth. However, (Fact A), they are not here; therefore they do not exist.
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- Information
- ExtraterrestrialsWhere Are They?, pp. 1 - 8Publisher: Cambridge University PressPrint publication year: 1995
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