On Sunday I quickly read Probability 1 by Amir Aczel. While the book is a solid introduction to basic space-related information that anyone who has watched the Discovery Channel in the past fifteen years already knows, the ending chapters of the book are the crux of Dr. Aczel’s argument.
In brief, he argues that because the existence of life on any given planet is independent of the probability of life on any other given planet, then the probability of intelligent life on another planet is
1 – Probability of Life Not on Any Given Planet ^ # of Planets
Because any fraction taken by itself enough approaches zero, this means the probability of intelligent life approaches one. Therefore, there is intelligent life elsewhere in the universe (and, for that matter, probably the galaxy)
However, Dr. Aczel’s argument is easily disposed of, because the trials are not independent. Indeed, there may not be intelligent life on many planets for the same reason. Analogously, imagine you determine the probability of a driver pulling over at any given minute, and from there attempt to determine the number of individuals who have driven from Nebraska to Pitcairn Island. Statistical sleight of hand along the line of Amir Aczel’s may arrive at any number of answers, with a 100% probability that at least one individual has driven that long. Of course, the trials are not independent in such an example: all drivers would be frustrated by the lack of a bridge across the Pacific.