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

TL;DR

This paper uses Bayesian analysis to explore Fermi's paradox, examining how prior assumptions influence conclusions about the likelihood of extraterrestrial life and humanity's future in the universe.

Contribution

It critically evaluates the impact of prior distributions on Bayesian inferences related to extraterrestrial life and the Great Filter hypothesis.

Findings

Bayesian conclusions depend heavily on prior choices.

Discovery of extraterrestrial life suggests high p but small q.

Prior assumptions significantly influence the interpretation of Fermi's paradox.

Abstract

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.