I hadn’t seen the Lineweaver and Davis paper before, thanks for pointing it out! I’m sceptical of the methodology, though. They start out with a uniform prior between 0 and 1 of the probability that life emerges in a ~0.5B year time window. This is pretty much assuming their conclusion already, as it assigns <0.1% probability to life emerging with less than 0.1% probability (I much prefer log-uniform priors). The exact timing of abiogenesis is then used to get a very modest bayesian update (less than 2:1 in favor of “life always happens as soon as possible” vs any other probability of life emerging) which yields the 95% credible interval with 13% at the bottom. Note that even before they updated on any evidence, they had already assumed a 95% credible interval with 2.5% at the bottom!

As an aside, I do mostly agree that alien life is likely to be common outside our galaxy (or at least that we should assume that it is). However, this is because I’m sympathetic to another account of anthropics, which leads to large numbers of aliens almost regardless of our prior, as I explain here.

I hadn’t seen the Lineweaver and Davis paper before, thanks for pointing it out! I’m sceptical of the methodology, though. They start out with a uniform prior between 0 and 1 of the probability that life emerges in a ~0.5B year time window. This is pretty much assuming their conclusion already, as it assigns <0.1% probability to life emerging with less than 0.1% probability (I much prefer

log-uniform priors). The exact timing of abiogenesis is then used to get a very modest bayesian update (less than 2:1 in favor of “life always happens as soon as possible” vsanyother probability of life emerging) which yields the 95% credible interval with 13% at the bottom. Note that evenbeforethey updated on any evidence, they had already assumed a 95% credible interval with 2.5% at the bottom!As an aside, I do mostly agree that alien life is likely to be common outside our galaxy (or at least that we should assume that it is). However, this is because I’m sympathetic to another account of anthropics, which leads to large numbers of aliens almost regardless of our prior, as I explain here.