COSMIC EVOLUTION: The Rise of Complexity in Nature. By Eric Chaisson. Harvard Univ. Press. 274 pp. $27.95

If you want to patent a perpetual motion machine, be sure you have a working model. The U.S. Patent Office, flooded with doodlings by hopeful inventors, has long since decided that it won’t examine claims for a perpetuum mobile without the article in hand.

Which, of course, rules out a patent, because a perpetual motion machine falls afoul of that ultimate trump card, the Second Law of Thermodynamics. "If your theory is found to be against the Second Law of Thermodynamics," Sir Arthur Eddington once mused, "I can give you no hope; there is nothing for it but to collapse in deepest humiliation."

Roughly speaking, the Second Law states that the disorder in the universe—its entropy—is always increasing. An ordered state, such as a box with hot air on one side and cold air on the other, will quickly deteriorate and become lukewarm throughout. But how can a universe slouching toward disorder have such orderly structures as galaxies, stars, bacteria, and people? To Harvard University astrophysicist Chaisson, this interplay between order and disorder, between energy and entropy, holds the answer to the age-old question, "What is life?"

As Chaisson describes in Cosmic Evolution, the Second Law has a little loophole—not really an exception, but a means for eking out an existence in a universe that’s inexorably falling apart. Energy lets us make order out of disorder. An air conditioner, plugged into a wall socket, can turn a zone of lukewarm air into one with hot air on one side and cold air on the other, reversing the disorder, at least locally. Organisms do this too, taking in energy in the form of food, which keeps their bodies from literally disintegrating. So Chaisson defines life as an "open, coherent, space-time structure maintained far from thermodynamic equilibrium by a flow of energy through it." This definition covers not only bacteria and people, but stars, galaxies, and planets as well. To Chaisson, the Earth is a living object that differs only in degree from an ostrich or an aardvark.

The problem with such a broad definition of life is that it becomes meaningless; cosmic evolution parallels biological evolution only in the most general sense. Still, Chaisson does give the theory some numerical muscle. He analyzes the flows of energy through various objects and shows how these flows seem to be related to the complexity of the objects. The greater the energy flow, the greater the complexity. Though following the nuances of the argument requires a basic grounding in physics, Chaisson’s approach leaves one wondering, perhaps absurdly: Are hummingbirds "higher" than humans on the evolutionary ladder? Are jet engines "alive?" In this creative, thought-provoking book, Chaisson shows how difficult even the most basic scientific questions can turn out to be.

—Charles Seife