Essay:Commentary on Conservapedia's article on the second law of thermodynamics

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This is taken from some material that has been on my (User:SamHB) user page for some time.

There seems to be a good deal of confusion and unclear writing in the article Second Law of Thermodynamics.

The subject of thermodynamics, including the second law, was well established during the 19th century, by such people as Carnot, Gibbs, Clausius, Clapeyron, Maxwell, Helmholtz, and Thompson (Lord Kelvin). This long predates the advent of quantum mechanics. The subject of statistical mechanics, and the "randomness" or "uncertainty" were well understood. It does not depend on the uncertainty (the "Heisenberg uncertainty principle") of quantum mechanics.

There are two generally recognized types of "perpetual motion machine." A "perpetual motion machine of the first kind", which is what people generally mean when they use this term, is one that violates conservation of energy. Since the first law of thermodynamics is just conservation of energy, such a machine would violate the first law.

Such a perpetual motion machine is generally taken to mean one that actively gives out nonzero energy (you can see ads for these things on the internet[1][2][3]), rather than one that simply holds its own, even though a machine that holds its own, that is, never runs down, could obviously be considered a "perpetual motion machine."

Entities that hold their own and never run down actually do exist. Atoms are examples of them. The electrons orbiting the nucleus, if they are in their ground state, never stop. They never lose energy at all. (OK, the fact that they never lose energy depends on quantum mechanics, and I said above that quantum mechanics isn't involved, but the radiation from accelerating charges was unknown when thermodynamics was formulated.) Other things that never stop are quantum-mechanical harmonic oscillators, and gas molecules in their random motion. The latter was central to the kinetic theory that led to the development of thermodynamics. That is, the people developing thermodynamics were aware of the perpetual, never running down, nature of gas molecules. They postulated, correctly, that gas molecule collisions are perfectly elastic and never lose energy. They really are "perpetual motion machines."

The second law of thermodynamics relates to a more obscure fictional device, a "perpetual motion machine of the second kind." This would be something that violates the second law by causing heat to travel, without introduction of energy from an external source, from a colder body to a warmer one. In fact, it can be shown (and was shown in the 19th century), that any heat engine more efficient than that required by Carnot's law is impossible, because it would permit the construction of a machine that moved heat from a colder body to a warmer one.

From looking at the edit history of the article, there seems to be something of an edit war involving an insistence that the impossibility of a perpetual motion machine be described using the word "derail". This is an extremely unhelpful word, suggesting a similarity with a railroad train running off its tracks, and seems to be an attempt to evoke the commonsense notion of macroscopic mechanical devices wearing out due to friction. The second law is actually very clear in what it states and does not state. The article also muddies the thinking by including a folksy and cute, but woefully imprecise, layman's description by a famous science fiction author. While it is true that a person's room will tend to get messy if not attended to, and shuffling a deck of cards leads to more disorder, this is related to statistics, and involves an entropy change that is utterly minuscule compared with what goes on in thermodynamics. The "intelligent intervention" that the article describes (cleaning up the room, or sorting the cards) is statistically infeasible in the thermodynamics case. In fact, the scientists formulating the second law of thermodynamics considered this, in the form of a "Maxwell's demon", and showed that it was impossible.

The claim that the second law of thermodynamics disproves relativity or evolution is too preposterous to reply to.