Last week my former PhD supervisor Geraint Lewis visited us here in Auckland. The main reasons were to work on gravitational lens modelling with myself and my PhD student David Huijser, and also to attend a cosmology conference. Those things went well, but as per usual we also drifted off into many conversations about more crazy ideas to do with life, the universe and everything.
Years ago a paper came out by Charlie Lineweaver and Tamara Davis, about the formation of life on Earth. There is a popular argument that goes, “We know life formed pretty early on in terms of Earth’s history. Therefore abiogenesis is easy and life is common in the universe”. The Lineweaver and Davis paper made this argument quantitative, so we could say exactly how strong the evidence is in this direction. Unfortunately the paper also contained an unintentional highly informative prior that made the argument much stronger than it should have been. So I wrote up my response which was rejected by two journals. The basic conclusion is that the early formation of life does provide some evidence that life is “easy to form”, but not enough to convince a skeptic who thinks life is extremely rare. Some other authors independently came to the same conclusion.
Geraint is interested in generalisations and more realistic versions of this argument. But I’m not confident in any model that I write down until I understand the anthropic complications surrounding the argument (we couldn’t find ourselves on a planet where life didn’t form, etc). So I’ve given myself the task of reading and understanding Radford Neal’s tour de force on the subject before I deign to try anything.