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Talk:Second Law of Thermodynamics (view source)
Revision as of 04:51, June 14, 2012
, 04:51, June 14, 2012no edit summary
::::::::::: The melting of ice is simply a phase change to reflect the temperature. Refreeze the water and it's back to where it started. Observing water rather than ice is logically the same as observing the temperature on a nearby thermometer. This doesn't illustrate the basic truth that a [[perpetual motion machine]] is impossible. Do you think a perpetual motion machine -- one that that moves forever in a consistent manner without intelligent intervention -- may be possible?--[[User:Aschlafly|Andy Schlafly]] 23:34, 13 June 2012 (EDT)
::::::::::: The melting of ice is simply a phase change to reflect the temperature. Refreeze the water and it's back to where it started. Observing water rather than ice is logically the same as observing the temperature on a nearby thermometer. This doesn't illustrate the basic truth that a [[perpetual motion machine]] is impossible. Do you think a perpetual motion machine -- one that that moves forever in a consistent manner without intelligent intervention -- may be possible?--[[User:Aschlafly|Andy Schlafly]] 23:34, 13 June 2012 (EDT)
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While this isn't really my area a scientific expertise, there are a few things I'd like to say.
1. Perhaps a "layman's dictionary" definition of entropy could get away with just saying it's a measure of disorder, but that really isn't good enough for a web site that prides itself on its articles on science and math. Look at the [[Banach-Tarski Paradox]] for an example of the sophistication we have. By the way, my Webster's New Twentieth Century (yeah, it's out of date) Dictionary is a layman's dictionary, albeit unabridged. It gives its first definition as "a thermodynamic measure of the amount of energy unavailable for work in a system undergoing change." In any case, if you use the hand-wavy "disorder" definition, you can't then talk about thermodynamics and the fact that entropy increases. You'd have to explain how the act of cleaning one's room, or sorting a deck of cards, doesn't violate the second law. Of course we know why it doesn't, but we can't explain that without at least some thermodynamic terms. One needs to understand the connection between decks of cards naturally becoming ordered when we shuffle them, and heat spontaneously flowing from a colder object to a warmer one. It's not simple.
2. The connection between iron and rust, and the connection between wood and ashes, is not one of "disintegration". Iron does not disintegrate when it rusts. (In fact, because of its place on the nuclear binding energy graph, iron is the most indestructible element that there is.) Iron combines with oxygen. That is a chemical reaction, and it can be reversed, though, unfortunately, it doesn't naturally reverse itself when rusty objects are left outside. An understanding of how chemical reactions work, and how they can be reversed, is the result of the hundreds of years of research, first by the alchemists, followed by the more careful research of people like Priestley, Lavoisier, Dalton, Scheele, Gay-Lussac, and many others.
3. The oxidation of wood to make ash (it's more complicated than that, actually) is another chemical reaction, and it is also reversible. Trees burn down all the time. The ash goes into the ground, and, eventually, the forest grows back. The cycle repeats again and again, all over the world. The change in entropy between water and ice also goes in cycles, every year. When water freezes in winter, the entropy goes down. When the ice thaws, it goes up. Repeatedly. The heat budget of the Sun-Earth system (warm in summer, cold in winter) is easily enough to drive the entropy of all of these reactions. The same thing is true of salts going between solution (disorder, and high entropy) and crystals (order, and low entropy.) The energy needed to make these reactions go back and forth is easily available, from, say, a Bunsen burner. Or just leaving something out to dry.
4. The same sort of thing happens in the field of biology. The transition from a bunch of amino acids (disordered system) into, say, a kidney (ordered system) can take place easily, because the necessary energy is available. By the way, the force involved in turning amino acids into kidneys is related to the force turning a salt solution into a crystal. The ribosomes that put an amino acid into place are acting under electrostatic forces, albeit in a much more complex pattern than a positive Sodium ion falling into place next to a negative Chlorine ion.
5. In discussing the second law, one must keep in mind that there are two kinds of hypothetical "perpetual motion machines." A "perpetual motion machine of the first kind" violates the first law of thermodynamics, that is, conservation of energy. It is what people usually think of when they talk about perpetual motion machines. A "perpetual motion machine of the second kind" violates the second law of thermodynamics. It makes a cold thing colder and a hot thing hotter, while conserving energy. That is, it moves heat "uphill" without any external energy source.
6. Biological evolution is, of course, more complicated than all that. Whether the second law makes biological evolution impossible is a complicated question, and I have to defer to scientists who have studied this in much more detail than I.
[[User:JudyJ|JudyJ]] 00:51, 14 June 2012 (EDT)