Second law of thermodynamics

The second law of thermodynamics is a law of thermodynamics that states that all work tends towards the production of greater entropy over time. Another way of saying this (known as the Clausius formulation) is that it is impossible to construct a perfect refrigerator. (This is why refrigerators always require an external power source.) An equivalent statement, known as the Kelvin-Planck formulation, is that "It is impossible for any cyclic process to occur whose sole effect is the extraction of heat from a reservoir and the perfromance of an equivalent amount of work." (If the reader is aware of the concept of heat engines, please understand that heat engines work by allowing two heat reservoirs of different temperatures to come in equilibrium with each other, and as such they do not violate the 2nd law.)

Evolution, creation, and the second law

Creationists often use the second law of thermodynamics to argue against evolution, both on a cosmological and biological scale. In modern physics, the universe as a whole is taken to be a thermodynamically isolated system. The second law says that the entropy of an isolated system inevitably increases, and thus creationists argue that cosmological models involving the universe becoming more ordered are therefore false. Most scientists believe that current cosmological models are compatible with the second law, since the universe goes from something small and hot to a larger and colder arrangement--all in accord with the second law and an overall increase in entropy despite some localized decreases.

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Popular misunderstandings of creationist claims

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Creationists have also attempted to use the second law against biological evolution. However, while many creationists have claimed that the second law poses a nasty problem for evolution, how the law poses a problem is often misunderstood. The typical argument seems to be that the second law implies a general tendency of order towards disorder, and evolution lacks the means to overcome this tendency. Anticreationists have sometimes misunderstood the argument at hand, confusing ?tendency? to mean ?invariability,? thus resulting in anticreationists refuting the ?entropy never decreases? claim. Local decreases in entropy such as crystallization, where there is a localized increase in order (at the expense of a net increase in entropy for the universe as a whole) effectively refute the ?entropy never decreases? claim. However, this does not attack the actual mainstream creationist position since they have argued tendency, not invariability. Some critics claim that this misunderstanding is at least partly the fault of the creationists, who have not always made their positions clear.

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A related argument that involves misunderstanding of the creationist position is the ?open system argument.? The second law says that entropy cannot decrease in an isolated system. What the open system argument points out is that the earth is not an isolated system because the sun's energy constantly bathes the planet. Therefore entropy can decrease (and ?order? can increase) for evolution to work. This response, however, does not attack the actual creationist position. When it comes to the second law itself making a truly direct contradiction against evolution, creationists have in mind the cosmological evolution model (to which many anticreationists have mistakenly taken this claim to apply to biological evolution), which is applied to an isolated system (the universe as a whole). As indicated earlier, the scientific response to this is that in terms of thermodynamics, the universe was at its most "ordered" (i.e. lowest total entropy) at the time of the Big Bang, and the total entropy has been increasing ever since.

Related Topics:
Entropy - Big Bang

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Notably, even some creationists have misunderstood their own proponents and claimed a ?direct contradiction? between the second law and biological evolution. When it comes to biological evolution, the second law argument is usually applied differently. Creationists claim that certain criteria in addition to an open system are needed for order (at least the sort of order evolution requires to increase in organisms) to increase and overcome the general tendency towards disorder that the second law implies, furthermore claiming that evolution does not meet all of these criteria.

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Nonetheless, the vast majority of scientists believe such creationist claims to be false and that the second law poses no real problem for biological evolution. Among scientists whose formal training includes thermodynamics, this view is virtually (albeit not totally) universal.

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