Thursday, October 11, 2007

Second Law of Thermodynamics and Complex Systems

I found this rather good explanation of why the creationists favourite 'evidence' against evolution, that the second law of thermodynamics is incompatible with the formation of complex systems, is simply wrong.

Complex systems

It is occasionally claimed that the second law is incompatible with autonomous self-organisation, or even the coming into existence of complex systems. This is a common creationist argument against evolution.[9] The entry self-organisation explains how this claim is a misconception.
In fact, as hot systems cool down in accordance with the second law, it is not unusual for them to undergo spontaneous symmetry breaking, i.e. for structure to spontaneously appear as the temperature drops below a critical threshold. Complex structures, such as Bénard cells, also spontaneously appear where there is a steady flow of energy from a high temperature input source to a low temperature external sink. It is conjectured that such systems tend to evolve into complex, structured, critically unstable "edge of chaos" arrangements, which very nearly maximise the rate of energy degradation (the rate of entropy production).[10]
Furthermore, the concept of entropy in thermodynamics is not identical to the common notion of "disorder". For example, a thermodynamically closed system of certain solutions will eventually transform from a cloudy liquid to a clear solution containing large "orderly" crystals. Most people would characterize the former state as having "more disorder" than the latter state. However, in a purely thermodynamic sense, the entropy has increased in this system, not decreased. The units of measure of entropy in thermodynamics are "units of energy per unit of temperature". Whether a human perceives one state of a system as "more orderly" than another has no bearing on the calculation of this quantity. The common notion that entropy in thermodynamics is equivalent to a popular conception of "disorder" has caused many non-physicists to completely misinterpret what the second law of thermodynamics is really about.

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