Useful arxiv link: https://arxiv.org/abs/2004.03968 https://arxiv.org/abs/2004.03968 As always, the critical assumption is f_l, the probability that life of an

Useful arxiv link: https://arxiv.org/abs/2004.03968 https://arxiv.org/abs/2004.03968 As always, the critical assumption is f_l, the probability that life of any kind will originate on a "suitable" planet. The authors invoke the "Principle of Mediocrity", which says something like, "We're not special, therefore f_l = 1". This is exact opposite of the Anthropic Principle, which says: "From the observation that life has originated on Earth, we can deduce nothing at all about f_l." If f_l is some other number, like 0.00000000000000000000000000000000000000001, then the expected number of alien civilisations won't be 36, it will be 0.00000000000000000000000000000000000000036. Also 0.00000000000000000000000000000000000000001 could be wildly optimistic. The true value might have so many zeroes after the decimal point that it exceeds the permitted size of Hacker News comments.