Nick Bostrom, Max Tegmark | How Unlikely is a Doomsday Catastrophe?

Max Tegmark (1) & Nick Bostrom (2)

1. Department of Physics, Massachusetts Institute of Technology,
Cambridge, MA02139, USA
2. Future of Humanity Institute, Faculty of Philosophy,
Oxford University, OX14JJ, Oxford, UK

(Dated: December 18, 2005. This paper is an extended version of the Brief Communication published in Nature, 438, 754[1].)

Numerous Earth-destroying doomsday scenarios have recently been analyzed, including breakdown of a metastable vacuum state and planetary destruction triggered by a "strangelet'' or microscopic black hole. (Tegmark/Bostrom) point out that many previous bounds on their frequency give a false sense of security: one cannot infer that such events are rare from the the fact that Earth has survived for so long, because observers are by definition in places lucky enough to have avoided destruction. (Tegmark/Bostrom) derive a new upper bound of one per 10^9 years (99.9% c.l.) on the exogenous terminal catastrophe rate that is free of such selection bias, using planetary age distributions and the relatively late formation time of Earth.

FIG. 1: The left panel shows the probability distribution for observed planet formation time assuming catastrophe timescales τ of ∞ (shaded), 10, 9, 8, 7, 6, 5, 4, 3, 2 and 1 Gyr, respectively (from right to left). The right panel shows the probability of observing a formation time ≥9.1 Gyr (that for Earth), i.e., the area to the right of the dotted line in the left panel.

Hence (their) result closes the logical loophole of selection bias and gives reassurance that the risk of accelerator-triggered doomsday is extremely small, so long as events equivalent to those in our experiments occur more frequently in the natural environment.