Extraterrestrials: Where Are They?

Is it possible that extraterrestrial life forms exist within our Galaxy, the Milky Way? This book offers a critical analysis by leading experts in a range of sciences, of the plausibility that other intelligent lifeforms do exist. Exploration of the Solar System, and observations with telescopes that probe deep space, have come up empty handed in searches for evidence of extraterrestrial life. Many experts in the fields of astronomy, biology, chemistry and physics are now arguing that the evidence points to the conclusion that technological civilisations are rare. After ten billion years, and among hundreds of billions of stars, we may well possess the most advanced brains in the Milky Way Galaxy. This second edition contains many new and updated aspects of extraterrestrial research, especially the biological viewpoint of the question.


• Completely scientific presentation, robustly argued • Contact with an extraterrestrial civilisation would be the most dramatic scientific discovery of all time • Second edition is thoroughly up to date and includes new research

Contents 
1. An explanation for the absence of extraterrestrials on Earth Michael H. Hart; 2. One attempt to find where they are: NASA's high resolution microwave survey Jill Tarter; 3. An examination of claims that extraterrestrial visitors to Earth are being observed Robert Sheaffer; 4. The likelihood of interstellar colonization, and the absence of its evidence Sebastian von Hoerner; 5. Preemption of the galaxy by the first advanced civilization Ronald Bracewell; 6. Stellar evolution: motivation for the mass interstellar migrations Ben Zuckerman; 7. Interstellar propulsion systems Freeman Dyson; 8. Interstellar travel: a review Ian A. Crawford; 9. Settlements in space, and interstellar travel Cliff Singer; 10. Terraforming James Oberg; 11. Estimates of expansion time scales Eric M. Jones; 12. A search for tritium sources in our Solar System may reveal the presence of space-probes from other stellar systems Michael D. Papagiannis; 13. Primordial organic cosmochemistry Cyril Ponnamperuma and Rafael Navarro-Gonzalez; 14. Chance and the origin of life Edward Argyle; 15. The RNA world: life before DNA and protein Gerald F. Joyce; 16. The search for extraterrestrial intelligence Ernst Nayr; 17. Alone in a crowded universe Jared Diamond; 18. Possible forms of life in environments very different from the Earth Robert Shapiro and Gerald Feinberg; 19. Cosmological SETI frequency standards J. Richard Gott, III; 20. Galactic chemical evolution: implications for the existence of habitable planets Virginia Trimble; 21. The frequency of planetary systems in the galaxy Jonathan I. Lunine; 22. Atmospheric evolution, the Drake equation, and DNA: sparse life in an infinite universe Michael H. Hart.