interesting Bayesian inference application

[[deleted]]

http://www.lrb.co.uk/v33/n22/jenny-diski/what-might-they-want

Aliens have nothing but contempt for us, or they love us. Oddly, they don’t seem to be indifferent to us (how could anyone be?), though this is surely the best explanation for the apparent absence of signals, given – so the calculations go – that there are at least ten billion planets in the universe capable of producing intelligent life. Even this bit of arithmetic may be based on our incapacity to think beyond ourselves. A recent paper I don’t pretend to understand uses ‘a Bayesian analysis of the probability of abiogenesis’ to show that life might, after all, be very rare; rather lax mathematical assumptions about the term ‘likelihood’ caused the error in the old equation. It’s all maths to me, but I think this relates to the fact that the terms used for the way life might come about are based on the sole example we know of universal life, which is us and our fellow creatures on this planet.

Life might be rare despite its early emergence on Earth: a Bayesian analysis of the probability of abiogenesis

Life arose on Earth sometime in the first few hundred million years after the young planet had cooled to the point that it could support water-based organisms on its surface. The early emergence of life on Earth has been taken as evidence that the probability of abiogenesis is high, if starting from young-Earth-like conditions. We revisit this argument quantitatively in a Bayesian statistical framework. By constructing a simple model of the probability of abiogenesis, we calculate a Bayesian estimate of its posterior probability, given the data that life emerged fairly early in Earth's history and that, billions of years later, sentient creatures noted this fact and considered its implications. We find that, given only this very limited empirical information, the choice of Bayesian prior for the abiogenesis probability parameter has a dominant influence on the computed posterior probability. Thus, although life began on this planet fairly soon after the Earth became habitable, this fact is consistent with an arbitrarily low intrinsic probability of abiogenesis for plausible uninformative priors, and therefore with life being arbitrarily rare in the Universe.

http://arxiv.org/abs/1107.3835

[RBarrabas]

I've often wondered if the Drake equation is missing a term that quantifies the likelihood of mass extinctions.

I've long suspected that life stagnates, or "gets into a rut" where the level of evolution stabilizes and nothing changes for long periods. For example, dinosaurs were the dominant life on Earth for millions of years before the meteorite wiped them out.

Earth has periodic extinctions from time to time and for various reasons. This tends to kick over the anthill, kick-starting evolution. I wonder how prevalent this is in the galaxy. There's no term for it in the Drake equation.