Two big ideas often come up in discussions about the search for extraterrestrial intelligence, or SETI. One is the Drake Equation, which estimates the number of civilizations in our Galaxy whose signals we might be able to detect--potentially thousands, according to plausible estimates. The other is the so-called Fermi paradox, which claims that we should see intelligent aliens here if they exist anywhere, because they would inevitably colonize the Galaxy by star travel--and since we don't see any obvious signs of aliens here, searching for their signals is pointless. The Drake Equation is perfectly genuine: it was created by astronomer...