The story goes like this: Sometime in the 1940s, Enrico Fermi was talking about the possibility of extraterrestrial intelligence with some other physicists. They were impressed that life had evolved quickly and progressively on Earth. They figured our galaxy holds about 100 billion stars, and that an intelligent, exponentially-reproducing species could colonize the galaxy in just a few million years. They reasoned that extraterrestrial intelligence should be common by now. Fermi listened patiently, then asked, simply, "So, where is everybody?" That is, if extraterrestrial intelligence is common, why haven't we met any bright aliens yet? This conundrum became known as Fermi's Paradox.