Dave5

Crawford and Schulze-Makuch ask a blunt question in the title of their paper in Nature Astronomy: ”Is the apparent absence of extraterrestrial technological civilizations down to the zoo hypothesis or nothing?” The zoo hypothesis posits that we are being studied by beings that for reasons of their own avoid contact. David Brin referred in his classic 1983 paper “The Great Silence” (citation below) to this as one variation of a quarantine, with the Solar System something like a nature preserve whose inhabitants have no idea that they are under observation.

Quarantines can come in different flavors, of course. Brin notes the possibility that observers might wait for our species to reach a level of maturity sufficient to join what could be a galactic ‘club’ or network. Or perhaps the notion is simply to let planets early in their intellectual development lie fallow as their species mature. Wilder notions include the idea that we could be quarantined because we represent a danger to the existing order, though it’s hard to imagine a scenario in which this occurs.

But the Crawford / Schulze-Makuch paper is not exactly a defense of the zoo hypothesis.