My friend and colleague Stuart Armstrong gave a talk titled von Neumann probes, Dyson spheres, exploratory engineering and the Fermi paradox to the physics department yesterday.
It is based on a paper we are writing together that analyses how much harder the Fermi question (because it is not really a paradox, just a question with answers we tend to dislike/disagree on) becomes once you take modern ideas about self replication and exploratory engineering into account. The main finding is that intergalactic expansion is likely doable using local resources and a very high branching factor, and that makes the solar neighbourhood accessible to at least millions of times more potential alien civilizations. So either alien civilizations have to be even rarer than we think, they have to approach some non-visible behavioural attractor with very high fidelity, or they are here and hiding efficiently (in this case likely because the first expanding civilization used its probes to enforce some set of rules for everybody else).
My friends who happen to be members of the Enceladus Protection Society will be happy to know that no moons of Saturn were harmed in this analysis.
Posted by Anders3 at February 1, 2012 03:27 PM