SETI & Technosignatures

Deconstructing Alien Hunting

By Keith Cowing
Status Report
November 17, 2023
Filed under , ,
Deconstructing Alien Hunting
Schematic of the four possible branches resulting from an experiment of a randomly selected target, where the experiment seeks to detect a phenomenon which occurs within a fraction f of the targets under consideration, and the experiment has a confounding positive probability of CPP and a true positive probability of TPP. — astro-ph.IM

The search for extraterrestrial (alien) life is one of the greatest scientific quests yet raises fundamental questions about just what we should be looking for and how.

We approach alien hunting from the perspective of an experimenter engaging in binary classification with some true and confounding positive probability (TPP and CPP). We derive the Bayes factor in such a framework between two competing hypotheses, which we use to classify experiments as either impotent, imperfect or ideal. Similarly, the experimenter can be classified as dogmatic, biased or agnostic. We show how the unbounded explanatory and evasion capability of aliens poses fundamental problems to experiments directly seeking aliens.

Instead, we advocate framing the experiments as looking for that outside of known processes, which means the hypotheses we test do not directly concern aliens per se. To connect back to aliens requires a second level of model selection, for which we derive the final odds ratio in a Bayesian framework. This reveals that it is fundamentally impossible to ever establish alien life at some threshold odds ratio, crit, unless we deem the prior probability that some as-yet-undiscovered natural process could explain the event is less than (1+crit)−1.

This elucidates how alien hunters need to carefully consider the challenging problem of how probable unknown unknowns are, such as new physics or chemistry, and how it is arguably most fruitful to focus on experiments for which our domain knowledge is thought to be asymptotically complete.

David Kipping, Jason Wright

Comments: Accepted for publication in The Astronomical Journal
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM)
Cite as: arXiv:2311.08476 [astro-ph.IM] (or arXiv:2311.08476v1 [astro-ph.IM] for this version)
Submission history
From: David Kipping
[v1] Tue, 14 Nov 2023 19:08:25 UTC (759 KB)

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻