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Fermi's paradox, extraterrestrial life and the future of humanity: a Bayesian analysis

  • Vilhelm Verendel (a1) and Olle Häggström (a2)


The Great Filter interpretation of Fermi's great silence asserts that Npq is not a very large number, where N is the number of potentially life-supporting planets in the observable universe, p is the probability that a randomly chosen such planet develops intelligent life to the level of present-day human civilization, and q is the conditional probability that it then goes on to develop a technological supercivilization visible all over the observable universe. Evidence suggests that N is huge, which implies that pq is very small. Hanson (1998) and Bostrom (2008) have argued that the discovery of extraterrestrial life would point towards p not being small and therefore a very small q, which can be seen as bad news for humanity's prospects of colonizing the universe. Here we investigate whether a Bayesian analysis supports their argument, and the answer turns out to depend critically on the choice of prior distribution.


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Aldous, D.J. (2012). The great filter, branching histories and unlikely events. Math. Sci. 37(1), 5564.
Armstrong, S. (2011). Anthropic decision theory. arXiv:1110.6437.
Armstrong, S. & Sandberg, A. (2013). Eternity in six hours: intergalactic spreading of intelligent life and sharpening the Fermi paradox. Acta Astronaut. 89, 113.
Bostrom, N. (2002). Anthropic Bias: Observation Selection Effects in Science and Philosophy. Routledge, New York.
Bostrom, N. (2008). Where are they? Why I hope the search for extraterrestrial life finds nothing. MIT Technology Review May/June, 7277.
Bostrom, N. (2014). Superintelligence: Paths, Dangers, Strategies. Oxford University Press, Oxford.
Bostrom, N. & Cirkovic, M.M. (2008). Global Catastrophic Risks. Oxford University Press, Oxford.
Brandt, T.D. & Spiegel, D.S. (2014). Prospects for detecting oxygen, water, and chlorophyll on an exo-earth. Proc. Natl. Acad. Sci. 111(37), 1327813283.
Cassan, A. et al. (2012). One or more bound planets per Milky Way star from microlensing observations. Nature 481(7380), 167169.
Ćirković, M. (2009). Fermi's paradox: the last challenge for copernicanism? Serb. Astron. J. 178, 120.
Cox, D. & Hinkley, D. (1979). Theoretical Statistics. Chapman and Hall, London.
Griffith, R.L., Wright, J.T., Maldonado, J., Povich, M.S., Sigurdsson, S. & Mullan, B. (2015). The ĝ infrared search for extraterrestrial civilizations with large energy supplies. iii. The reddest extended sources in wise. Astrophys. J. Suppl. Ser. 217(2), 25.
Häggström, O. (2007). Uniform distribution is a model assumption.
Häggström, O. (2016). Here Be Dragons: Science, Technology and the Future of Humanity. Oxford University Press, Oxford. To appear.
Hanson, R. (1998). The great filter – are we almost past it?
Hart, M. (1975). Explanation for the absence of extraterrestrials on earth. Q. J. R. Astron. Soc. 16, 128135.
Martin, J. (2006). The Meaning of the 21st Century: A vital Blueprint for Ensuring our Future. Transworld, London.
Pamlin, D. & Armstrong, S. (2015). Global Challenges: 12 Risks that Threaten Human Civilization. Global Challenges Foundation, Stockholm.
Petigura, E.A., Howard, A.W. & Marcy, G.W. (2013). Prevalence of Earth-size planets orbiting sun-like stars. Proc. Natl. Acad. Sci. 110(48), 1927319278.
Quintana, E.V. et al. (2014). An Earth-sized planet in the habitable zone of a cool star. Science 344(6181), 277280.
Rees, M. (2003). Our Final Century: Will the Human Race Survive the Twenty-first Century? William Heinemann, London.
Salsburg, D. (2001). The lady tasting tea: How statistics revolutionized science in the twentieth century.
Tegmark, M. (2014). Our Mathematical Universe: My Quest for the Ultimate Nature of Reality. Allen Lane, London.
Webb, S. (2002). If the Universe is Teeming with Aliens… Where is Everybody?: Fifty Solutions to the Fermi Paradox and the Problem of Extraterrestrial Life. Copernicus Books, New York.
Wolfram, S. (2002). A New Kind of Science. Wolfram media, Champaigne, IL.


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Fermi's paradox, extraterrestrial life and the future of humanity: a Bayesian analysis

  • Vilhelm Verendel (a1) and Olle Häggström (a2)


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