Between the mid-1970s and early 1980s, two physicists, Michael Hart and Frank Tipler, published a controversial series of papers arguing that extraterrestrial intelligence didn't exist. As they argued, the likelihood that extraterrestrial civilizations (ETCs) would have had enough time to develop ad vanced computing, spaceflight and self-replicating machines (Von Neumann probes) means they would have colonized the galaxy, and come to Earth, long ago. Since there was no evidence of this, they reasoned that ETCs must not exist and humanity was alone in the universe. ...read more read less