"the second law"


The second law of thermodynamics is often misquoted - eps. in the
popular press and by physics students - and most especially by
creationists. It does NOT say that entropy always increases. It
says that in a CLOSED system in THERMAL EQUILIBRIUM, the entropy
always increases (or stays the same). Entropy, like temperature,
is defined for a system in thermal equilibrium - or at least that's
the situation in traditional thermodynamics from which the 3 laws
follow. Thermal equilibrium has to do with the way in which energy
is partitioned in the system - and a system if left alone will 
typically tend toward equilibrium. If the system is not in
equilibrium, such as the earth, then there isn't a globally well
defined entropy, so the second law does not apply (although it does
apply to approximately closed subsystems in equilibrium with themselves).

Creationists are either uninformed or dishonest if they use entropy
arguments against evolution. The earth is not a closed system for one
thing, and it isn't in thermal equalib. for another. There is, however,
a developing field of non-equalib. thermodynamics that attempts to
generalize the concept of entropy (amongst other things). You can define
a local entropy density and there are situations in which you can have
spontaneous decrease in entropy in one location at the expense of a
greater entropy increase in another location.
This is the situation of the earth-sun system. Hope this helps.

BTW - thermodynamics/statistical mechanics is not a fundamental
physical theory. It describes the behavior of matter in bulk if
certain conditions are met (i.e. thermal equalim.)

bob singleton
bobs@thnext.mit.edu