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Equation 4 · Part 5 · Comparing the Main Approaches to Origins of Life and Astrobiology

=

P(Hbio∣D)=P(D∣Hbio) P(Hbio)P(D∣Hbio) P(Hbio)+P(D∣Hab) P(Hab)P(H_{bio} \mid D) = \frac{P(D \mid H_{bio})\, P(H_{bio})}{P(D \mid H_{bio})\, P(H_{bio}) + P(D \mid H_{ab})\, P(H_{ab})}
=

What this part means

The expressions on both sides represent the same quantity under the stated assumptions.

Its job in the formula

The equals sign connects the complete expression on the left with the complete expression on the right. Both sides must have compatible units.

The passage around this formula

What lets these three very different kinds of evidence be compared at all is a shared logical structure that the Astrobiology community has tried to formalize explicitly rather than leave implicit. David Catling and coauthors proposed treating a biosignature detection as a Bayesian inference problem: a prior probability that a given planet or sample harbors life, updated by the likelihood of the observed data under a “life” hypothesis versus under one or more specific abiotic alternative hypotheses, yields a posterior probability rather than a binary yes-or-no verdict [ 7 ] . Written compactly, for a single candidate abiotic alternative HabH_{ab} competing with a life hypothesis HbioH_{bio} given…

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Learn the underlying idea

An equals sign says that the expression on its left and the expression on its right have the same value under the stated definitions and assumptions.

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Sources cited in the surrounding passage

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