Astrobiology (general)

False Positives And The Challenge Of Testing The Alien Hypothesis

By Keith Cowing
Status Report
November 22, 2023
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False Positives And The Challenge Of Testing The Alien Hypothesis
The complex problem of detecting biospheres is simplified to the analogous situation of determining whether a coin is fair or biased. If instead of testing the hypothesis “I have the biased coin,” we want to test the hypothesis that “this planet has a biosphere,” we can formulate it using a similar approach. Again, it depends on the probability a nonliving planet produces an observable, P(Obs|NL) (top right), and the prior confidence we have that the planet hosts a biosphere, P(Life) (bottom right). In both graphs we have assumed that P(Obs|Life) = 1.0 such that our observation is expected to be produced by all biospheres. P(Obs|NL) is the false positive rate— how often do abiotic worlds produce the observable. If P(Obs|NL) is low (on a logarithmic scale) we do not need a strong prior for the emergence of life in that environment to have significant confidence in our life detection claims. — astro-ph.EP

The origin of life and the detection of alien life have historically been treated as separate scientific research problems. However, they are not strictly independent. Here, we discuss the need for a better integration of the sciences of life detection and origins of life.

Framing these dual problems within the formalism of Bayesian hypothesis testing, we show via simple examples how high confidence in life detection claims require either

(1) a strong prior hypothesis about the existence of life in a particular alien environment, or conversely,
(2) signatures of life that are not susceptible to false positives.

As a case study, we discuss the role of priors and hypothesis testing in recent results reporting potential detection of life in the Venusian atmosphere and in the icy plumes of Enceladus. While many current leading biosignature candidates are subject to false positives because they are not definitive of life, our analyses demonstrate why it is necessary to shift focus to candidate signatures that are definitive. This indicates a necessity to develop methods that lack false positives, by using observables for life that rely on prior hypotheses with strong theoretical and empirical support in identifying defining features of life.

Abstract theories developed in pursuit of understanding universal features of life are more likely to be definitive and to apply to life-as-we-don’t-know-it. In the absence of alien examples these are best validated in origin of life experiments, substantiating the need for better integration between origins of life and biosignature science research communities.

Searra Foote, Pritvik Sinhadc, Cole Mathis, Sara Imari Walker

Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Popular Physics (physics.pop-ph); Populations and Evolution (q-bio.PE)
Cite as: arXiv:2207.00634 [astro-ph.EP] (or arXiv:2207.00634v1 [astro-ph.EP] for this version)
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Submission history
From: Cole Mathis
[v1] Fri, 1 Jul 2022 19:19:08 UTC (719 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) 🖖🏻