Like a black hole, Extraterrestrial Civilizations contracts, moving from a billion trillion possibilities to imaginable probabilities as Asimov shows how the origins of life and the conditions that permit it to evolve limit civilization to 540 planets in our galaxy. The information, ranging from early speculation about space to pulsars and red giants, is impressive and is lucidly presented; but the chain of logic leading to the title's assertion is as unstable as a mile-long game of crack-the-whip. While I respect Asimov's resistance to UFOs, a drunk's sighting of a purple saucer is, finally, as credible as Asimov's argument.

Asimov does wonder "where is everybody" from these civilizations. In the last chapters he discusses the presently insurmountable difficulties of interstellar travel and communication. We are not alone, but we might just as well be. Even so, Asimov ends with a Battlestar Galactica vision of the future. A hundred years ago people believed there were holes at the poles. Using Asimov's probabilistic methods, one can believe those holes just haven't been found yet. (pp. 58-9)