Enrico Fermi asked what was (to him) an obvious question: “where is everybody?”

“Fermi realized that any civilization with a modest amount of rocket technology and an immodest amount of imperial incentive could rapidly colonize the entire Galaxy. Within ten million years, every star system could be brought under the wing of empire. Ten million years may sound long, but in fact it's quite short compared with the age of the Galaxy, which is roughly ten thousand million years.”

resolution

• “there aren't any” theory
• “they are amongst us” theory
• “we dont see the zookeeper” theory
• various x-files based theories
• “we cant perceive them” theory