They Exist, But We Have Yet to See or Hear from Them

Abstract

The position many scientists take on the question of extraterrestrial life is the following. The Galaxy contains billions of habitable, Earth-like planets. Some of those planets, perhaps tens of thousands of them, are home to life. And on some of those planets ETCs exist that are technologically far in advance of our own. This conclusion seems to follow from the Principle of Mediocrity —the notion that Earth is a typical planet orbiting a common type of star in an ordinary part of the Galaxy. The principle has served science well since the time of Copernicus. Scientists who take this position, however, have to answer Fermi’s question. If ETCs exist, then why aren’t they here? At the very least, why haven’t we heard from them?