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"A Fresh Take on Disorder, or Disorderly Science?", by Adrian Cho. Science, 23 August 2002, pages 1268-9.
The title refers to a new definition of entropy, its proponents and opponents. The definition formulated by Ludwig Boltzmann, and accepted for almost a century, is that entropy is k(ln W), where k is constant and W is the number of "equivalent microscopic arrangements" of a system. Constantinos Tsallis of the Brazilian Center for Research in Physics has proposed that entropy be defined as k(W(1-q)-1)/(1-q) where q is a parameter (whose definition isn't entirely clear). A quick application of L'Hôpital's Rule shows that as q approaches 1, the limit of the proposed expression for entropy equals the standard expression. Tsallis says that the old formula for entropy applies when a system is in equilibrium, but his formula becomes relevant when a system is far from equilibrium. The article presents viewpoints from both sides as to the desirability of adopting Tsallis' formula.
--- Mike Breen
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