Do SETI Optimists Have a Fine-Tuning Problem?

In ecological systems, be it a garden or a galaxy, populations evolve from some initial value (say zero) up to a steady state equilibrium, when the mean number of births and deaths per unit time are equal.

This equilibrium point is a function of the birth and death rates, as well as the carrying capacity of the ecological system itself. The growth curve is S-shaped, saturating at the carrying capacity for large birth-to-death rate ratios and tending to zero at the other end.

We argue that our astronomical observations appear inconsistent with a cosmos saturated with ETIs, and thus SETI optimists are left presuming that the true population is somewhere along the transitional part of this S-curve. Since the birth and death rates are a-priori unbounded, we argue that this presents a fine-tuning problem.

Further, we show that if the birth-to-death rate ratio is assumed to have a log-uniform prior distribution, then the probability distribution of the ecological filling fraction is bi-modal – peaking at zero and unity. Indeed, the resulting distribution is formally the classic Haldane prior, conceived to describe the prior expectation of a Bernoulli experiment, such as a technological intelligence developing (or not) on a given world.

Our results formally connect the Drake Equation to the birth-death formalism, the treatment of ecological carrying capacity and their connection to the Haldane perspective.

David Kipping, Geraint Lewis

Comments: Submitted to IJA
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM); Earth and Planetary Astrophysics (astro-ph.EP); Popular Physics (physics.pop-ph); Populations and Evolution (q-bio.PE)
Cite as: arXiv:2407.07097 [astro-ph.IM] (or arXiv:2407.07097v1 [astro-ph.IM] for this version)
https://doi.org/10.48550/arXiv.2407.07097
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Submission history
From: David Kipping
[v1] Fri, 14 Jun 2024 13:21:48 UTC (1,423 KB)
https://arxiv.org/abs/2407.07097

Astrobiology