We used to imagine humanity populating the universe. In Isaac Asimov's Foundation (1952), mankind has established a vast multi-planetary empire by the year 47000. “There were nearly twenty-five million inhabited planets in the Galaxy,” Asimov wrote. “The population of Trantor [the imperial capital] … was well in excess of forty billions.”In Liu Cixin’s Three-Body Problem (2006), by contrast, we’re a cosmic rounding error, bracing ourselves for the terrifying Trisolaran invasion. As the trailer f...