Simple Crucial Flaw in Frank and Sullivan’s recent Astrobiology paper

A paper published in Astrobiology, A New Empirical Constraint on the Prevalence of Technological Species in the Universe, has been getting some uncritical press: CBS News, Science Daily, phys.org, MIT Technology Review

It’s crucially flawed. Here’s the problem:

We now turn to the specific question, ‘‘Has even one other technological species ever existed in the observable Universe?’’ We take N* = 2 · 10^22 for the total number of stars in the observable Universe (Silburt et al., 2015) To address our question, A is set to a conservative value ensuring that Earth is the only location in the history of the cosmos where a technological civilization has ever evolved. Adopting A = 0.01 means that in a statistical sense were we to rerun the history of the Universe 100 times, only once would a lone technological species occur. .. This limiting value .. can be considered to define a ‘‘pessimism line’’ in discussions of the prevalence of technological civilizations on a cosmic scale.

Frank and Sullivan assume the observable universe is the whole universe or they are unaware of anthropics. The pessimism line should be based on the whole universe. Since the universe is probably vast (even compared to our observable universe) or infinite, calculating the lower bound this way is useless.

With our approach we have, for the first time, provided a quantitative and empirically constrained limit on what it means to be pessimistic about the likelihood of another technological species ever having arisen in the history of the Universe.

All they did was take [1/stars in the universe] and multiplied it by the recent data about habitability rates! I’m sure others have done this and not considered it worth writing a paper about and also noticed that the stars in the observable universe are not all the stars.

They then preach on unrelated climate change issues for the final page, but I’ll let that slide.