** 4th book of 2021: Somewhere between zero and infinity **
In modernity, we accept that evidence and experimentation can lead us to answering some of life’s most important questions. By applying Bayesian reasoning, we can use priors and the accumulated body of evidence to evaluate new and sometimes deeply strange hypotheses like quantum physics. Yet for SETI, the priors point in opposite directions, creating Fermi’s Paradox: the one solar system we are close enough to investigate thoroughly has intelligent life. Every other part of the universe we have the tools to investigate reveals nothing, only an eerie silence.
How to proceed from this contradictory starting point is more philosophy than science, and even things like Drake’s Equation are more logical extrapolations than observations. As such, most of the book discusses the types of evidence that could be sufficient to prove alien life, and most of them come from just looking for weirdness: reverse chirality life, life with strange chemistry, space probes in our solar system, or intergalactic pollution. Strolling through hypotheses was a fun ride, learning what astrobiologists consider to be interesting such as whether life originated on mars or whether there have been multiple events of abiogenesis (https://en.wikipedia.org/wiki/Abiogenesis).