If the Universe Is Teeming With Aliens ... Where Is Everybody? Second Edition: Seventy-Five Solutions to the Fermi Paradox and the Problem of Extraterrestrial Life

Given the fact that there are perhaps 400 billion stars in our galaxy alone, and perhaps 400 billion galaxies in the universe, it stands to reason that somewhere out there, in the fourteen-billion-year-old cosmos, there is or once was a civilization at least as advanced as our own. The sheer enormity of the numbers almost demands that we accept the truth of this hypothesis. Why, then, have we encountered no evidence, no messages, no artifacts of these extraterrestrials?