kukacos#139
A zárt rendszer azért zárt rendszer, hogy hő sem szabadulhat ki belőle. Valamiért a hőt nem tekinted energiának, pedig pontosan ugyanolyan mozgási energia, mint az eldobott kavicsé, csak rendezetlen. Az entrópia növekedéséből következik az, hogy a válogatásod több energiát fog elemészteni, mint amit nyerhetsz a seprűzéssel. Lásd bővebben a Maxwell-démont:
http://en.wikipedia.org/wiki/Maxwell%27s_daemon
Maxwell imagines two containers, A and B, filled with the same gas at equal temperatures, placed next to each other. A little "demon" guards a trapdoor between the two containers, observing the molecules on both sides. When a faster-than-average molecule from A flies towards the trapdoor, the demon opens it, and the molecule will fly from A to B. Thus, the average speed of the molecules in B will have increased, while the molecules in A will have slowed down on average. However, since average molecular speed corresponds to temperature, the temperature in A will have decreased and in B will have increased; this is contrary to the second law of thermodynamics.
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Several physicists have presented calculations that show that the second law of thermodynamics will not actually be violated, if a more complete analysis is made of the whole system including the demon. The essence of the physical arguments is to show by calculation that any demon must "generate" more entropy segregating the molecules than it could ever eliminate by the method described. That is, it would take more effort to gauge the speed of the molecules and allow them to selectively pass through the opening between A and B than the amount of energy saved by the difference of temperature caused by this.