Ed Turner (Princeton) spent the day at NYU; we spoke about many things, from statistics to reductionism. He gave a nice seminar about abiogenesis—the emergence of life on the lifeless early Earth—which happened very early after the last surface-melting impacts. This implies, at some level, that abiogenesis at Earth conditions ought to be fairly likely. But that is complicated by anthropic-like issues and the single-number statistics involved. He applies Bayes' theorem and some uninformative priors to show that the data (or datum, really) does imply, weakly, a high rate of abiogenesis at Earth conditions. Turner's talk was followed by discussions with Bovy and Foreman-Mackey about projects.


  1. I tried to do this calculation once, and even wrote a (bad, not accepted) paper on it. The gist of my conclusion, if it is correct (I'm not convinced) is that the likelihood function does peak at short abiogenesis timescales, but asymptotes to a constant nonzero value at large timescales.

    So if we start out very sceptical about life in the universe, with an improper prior about the abiogenesis timescale, we don't learn enough to cancel out the impropriety.

  2. Brendon: I think Turner used essentially the same model as you did and came to the same conclusions. His criticism of L&D was also quite similar, if I remember correctly.