At one level, PROBABILITY ONE surveys recent findings about the existence of planets orbiting other sun-like stars, such as 51 Pegasi, discovered in 1995, Tau Bootis and others. Amir Aczel asks What is life? as well as: What is intelligent life? He examines the theories about how life evolved on earth from basic molecules, such as ammonia, into more complex organic compounds leading to DNA. The existence of similar molecules on other planets in our solar systems, as well as in meteorites that land on earth every year, are used in an argument for the evolution of such compounds - the building blocks of life - outside Earth. However, Aczel approaches his subject in a completely novel way, using the full power of modern probability theory. The laws of large numbers applied to the immense size of the known universe with its billions of galaxies, each containing many billions of stars, are used to argue the probability that there is life elsewhere. Aczel weaves the probability arguments seamlessly throughout a fascinating - and accessible - book.