The assumption behind SETI is that life—and intelligent life—is so prevalent that there must be millions if not billions of radio-capable civilizations in the universe (or at least within our light sphere, which refers to radio-broadcasting civilizations that were sending out radio waves early enough to reach Earth by today). Not a single one of them, however, has made itself noticeable to our SETI efforts thus far. So let’s consider the basic SETI assumption regarding the number of radio-capable civilizations from the perspective of the law of accelerating returns.
