They found that вЂњin any process in which a thermally isolated system goes from one macrostate to another, the entropy tends to increase (Reif 1965, 122).вЂќ It measures the вЂњdisorderвЂќ of a system in terms of the number of microstates-arrangements of molecules-accessible to a system in a given macrostate-having a particular temperature, pressure, and volume. That explanation led them to posit a strange quantity, one not directly observable: entropy.

Given its well behaved sibling, the first law of thermodynamics (that energy is always conserved, neither created nor destroyed), researchers sought a means of quantifying and explaining this energy transaction fee. So if we changed money back and forth, we would eventually go broke even with a fixed exchange rate. Whenever we exchange money, say from dollars to Euros, the bank charges a transaction fee.

Scientists and engineers discovered that, when trying to convert one form of energy, e.g., heat, into another form of energy, e.g., motion, we were never able to make the transfer complete, there was always some energy lost. The second law is best known as the principle that rules out perpetual motion, something resulting from its origin in the question вЂњhow efficient can we make steam engines?вЂќ-a strangely pragmatic starting point for such an esoteric principle. This is a common misunderstanding of one of the more baffling principles in physics, which has a long and contentious history, having been formulated in different ways by Sadi Carnot, Rudolf Clausius, William Thomson (Lord Kelvin), Ludwig Boltzmann, and Max Planck. The anti-evolutionistsвЂ™ argument is based on an understanding of the second law of thermodynamics, according to which disorder always increases.

Law of entropy