Tuesday, 16 October 2007

More on thermodynamics

I've stumbled onto an extract from this page, dealing with misconceptions about thermodynamics relating to evolution. I thought it might make a good supplement to my own writings on the subject; here's the relevant part:

This shows more a misconception about thermodynamics than about evolution. The second law of thermodynamics says, "No process is possible in which the sole result is the transfer of energy from a cooler to a hotter body." [Atkins, 1984, The Second Law, pg. 25] Now you may be scratching your head wondering what this has to do with evolution. The confusion arises when the 2nd law is phrased in another equivalent way, "The entropy of a closed system cannot decrease." Entropy is an indication of unusable energy and often (but not always!) corresponds to intuitive notions of disorder or randomness. Creationists thus misinterpret the 2nd law to say that things invariably progress from order to disorder.

However, they neglect the fact that life is not a closed system. The sun provides more than enough energy to drive things. If a mature tomato plant can have more usable energy than the seed it grew from, why should anyone expect that the next generation of tomatoes can't have more usable energy still? Creationists sometimes try to get around this by claiming that the information carried by living things lets them create order. However, not only is life irrelevant to the 2nd law, but order from disorder is common in nonliving systems, too. Snowflakes, sand dunes, tornadoes, stalactites, graded river beds, and lightning are just a few examples of order coming from disorder in nature; none require an intelligent program to achieve that order. In any nontrivial system with lots of energy flowing through it, you are almost certain to find order arising somewhere in the system. If order from disorder is supposed to violate the 2nd law of thermodynamics, why is it ubiquitous in nature?

The thermodynamics argument against evolution displays a misconception about evolution as well as about thermodynamics, since a clear understanding of how evolution works should reveal major flaws in the argument. Evolution says that organisms reproduce with only small changes between generations (after their own kind, so to speak). For example, animals might have appendages which are longer or shorter, thicker or flatter, lighter or darker than their parents. Occasionally, a change might be on the order of having four or six fingers instead of five. Once the differences appear, the theory of evolution calls for differential reproductive success. For example, maybe the animals with longer appendages survive to have more offspring than short-appendaged ones. All of these processes can be observed today. They obviously don't violate any physical laws.


There are two main objections that this author has to creationist claims. Firstly, entropy is not entirely synonymous with disorder as used in everyday language (although if you're careful with your physicist's definition, it's still perfectly usable). This wasn't a point I emphasised, since I thought it would be confusing. But it is worth remembering, and the distinction helps explain why, say, ice ("ordered") forms from water ("disordered") in very cold conditions. The entropy here goes up, but not the "disorder".

The second objection noted is the one I spent most of my time on in my own posts. Specifically, since our bodies are open systems, the restrictions imposed on closed systems by the first two thermodynamic laws simply don't apply. To my mind, this counterargument is absolutely fatal to this creationist objection.

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