A seeming exception to the dogma that everything eventually runs down is the phenomenon of life. If spontaneous processes always lead to disorder, how can a highly organized living creature survive?

There is a deceptive fallacy that maintains that life, by remaining superorganized, violates the second law of thermodynamics and therefore stands outside the purely natural order of things. The fallacy lies in applying a version of the second law, which is applicable only to isolated systems, to a living organism, which is very much an open thermodynamic system. In order to survive, all living creatures must have a constant influx of high-free-energy compounds, and must be able to get rid of a steady stream of entropy in the guise of disordered waste products. This continual supply of free energy is mandatory if the high level of organization of a living cell is to be maintained. Turn a living organism into a closed system by sealing it into an airtight steel coffin, and you will see how quickly it runs down.

The presumed paradox can be enlarged by one step. In view of the second law, how could such a highly organized, low-entropy phenomenon as life ever have evolved on Earth?

How can we maintain that the Earth is "running down," when the past three billion years have seen a progression from simple chemical compounds to Homo sapiens and his neighbours? The fallacy is the same.

The Earth is no more an isolated thermodynamic system than is a single individual. The Earth intercepts only a minute fraction of the energy radiated by the sun (approximately one part in two billion), but this energy is enough to keep the entire terrestrial clockwork running. When the sun dies, the Earth dies with it.

For all chemical and physical processes, the ultimate driving force is the same: free energy, G. For localized mechanical processes DS is negligible and DH is all-important. For isolated systems, including our entire universe, DH must be zero by definition and DS is crucial. These, however, are only two extremes of the generally applicable relationship DG = DH - TDS.