Abstract

Abstract. The presumptuous philosopher (PP) thought experiment lends more credence to the hypothesis which postulates the existence of a larger number of observers than other hypothesis. The PP was suggested as a purely speculative endeavor. However, there is a class of real world observer-selection effects where it could be applied, and one of them is the possibility of interstellar panspermia (IP). There are two types of anthropic reasoning: SIA and SSA. SIA implies that my existence is an argument that larger total number of observers exists; SSA implies that I should find myself in a region with larger number of observers. However, as S. Armstrong showed, SIA can’t distinguish between different ways how larger number of observers appeared, so it can’t favor IP compared with other ways to get many observers. SSA application here is less controversial as it tells only about relation between regions size: e.g. I am more likely to live in a larger country than in a small one, conditioning that the total number of small countries is also small. Anthropic considerations suggest that the universes in the multiverse with interstellar panspermia will have orders of magnitude more civilizations than universes without IP, and thus we are likely to be in such a universe. This is a strong counterargument against a variant of the Rare Earth hypothesis based on the difficulty of abiogenesis: even if abiogenesis is difficult, IP will disseminate life over billions of planets, meaning we are likely to find ourselves in a universe where IP has happened. This implies that there should be many planets with life in our galaxy, and renders the Fermi paradox even sharper. Either the Great Filter is ahead of us and there are high risks of anthropogenic extinction, or there are many alien civilizations nearby and of the same age as ours—which is itself a global catastrophic risk, as in that case the wave of alien colonization could arrive between 25-500 ky from now.