Entropy (thermodynamics)

"The most common way to describe entropy is as disorder... associated with things becoming more mixed, random and less ordered, but... the best way to think about entropy is as the tendency of energy to spread out. ...Most of the laws of physics work... the same... forwards or backwards in time. ...So how does this clear time dependence arise? ...[T]his is where Ludwig Boltzmann made an important insight. Heat flowing from cold to hot is not impossible, its just improbable. ...In everyday solids there are about 100 trillion trillion atoms and even more energy packets, so heat flowing from cold to hot is just so unlikely that it never happens. ...[I]f the ...tendency is to spread out and for things to get messier, then how is it possible to have ...air conditioning, where the cold interior gets cooler and the hot exterior gets hotter? Energy is going from cold to hot, decreasing the entropy of the house. ...[T]his ...is only possible by increasing the entropy a greater amount ...at a power plant ...heating up the environment ...and creating waste heat in the fans and compressor [of the air conditioner]. ...How is there any structure left on earth? ...[I]f the earth were a the energy would spread out completely, meaning all life would cease, everything would decay and mix, and ...reach the same temperature. But luckily the earth is not a closed system, because we have the sun."

"Because entropy is not really a classical quantity, we must build quantum mechanics into the definition. ... It suffices to define entropy as the logarithm of the number of quantum states accessible to a system."

"He sat in the window thinking. Man has a for order. Keys in one pocket, change in another. Mandolins are tuned G D A E. The physical world has a tropism for disorder, entropy. Man against Nature . . . the battle of the centuries. Keys yearn to mix with change. Mandolins strive to get out of tune. Every order has within it the germ of destruction. All order is doomed, yet the battle is worth while."

"Entropy is the price of structure."

"Investigations of the entropy of substances at low temperatures have produced very important information regarding the structure of crystals, the work of Giauque and his collaborators being particularly noteworthy. For example, the observed entropy of crystalline hydrogen shows that even at very low temperatures the molecules of orthohydrogen in the crystal are rotating about as freely as in the gas; ... subsequent to this discovery the phenomenon of rotation of molecules in crystals was found to be not uncommon."

"Is the random element... the only feature of the physical world which can furnish time with an arrow? ...Nothing in the statistics of an assemblage can distinguish a direction of time when entropy fails to distinguish one. ...[T]his law was only discovered in the last few years ...It is accepted as fundamental in ...atoms and radiation and had proved to be one of the most powerful weapons of progress in such researches. It does not seem to be... deducible from the second law..."

"Suppose we claim... heat flowing in the wrong direction, such as... ice forming in a glass of water... in an oven. ...Energy left the cool... water as heat, so the entropy went down. Because the temperature is low... in the denominator... that decrease in entropy is large. The same energy enters the hot region (...oven), so the entropy of that region increases. However... its temperature is high, [so] that increase in entropy is small. The net effect... a net decrease overall. ...[But] entropy never decreases, so heat cannot flow spontaneously... hot to cold..."

"Entropy was not in the same category as the other physical quantities ...and the extension ...was in a very dangerous direction. ...But entropy had secured a firm place in physics before it was discovered that it was a measure of the random element in arrangement. It was in great favour with the engineers. ...[A]t that time it was the general assumption that the Creation was the work of an engineer (not of a mathematician, as is the fashion nowadays)."

"I cannot read any significance into a physical world that is held... upside down. For that reason I am interested in entropy not only because it shortens calculations which can be made by other methods, but because it determines an orientation which cannot be found by other methods. ...[T]ime makes a dual entry and thus forms an intermediate link between the internal and the external. This is shadowed partially by the scientific world of primary physics (which excludes times arrow), but fully when we... include entropy. ...[It] has generally been assumed that the object of the quest is to find out all that really exists. There is another quest... to find out all that really becomes."

"In the limiting case, [entropy] stays the same. If it increases.., the process is irreversible. If it remains the same.., the process is reversible... [i.e.,] you can let it run backwards."

"The discrimination between cause and effect depends on times arrow and can only be settled by reference to entropy."

"Lets talk some energy transfer principles. ...My Grandpappy always used to say "hot goes to cold." ...Things of a higher energy intensity state tend to equalize with things at a lower intensity energy state. ...Where theres differences, things tend towards equilibrium... You put a ball on top of a hill and you give it a chance to roll down the hill, thats whats going to happen... If you leave a big pile of sand outside long enough, its going to flatten out. ...You take an ice cube and hold it in your hand ...heat goes out of your hand and melts the ice cube until that water becomes the same temperature as your hand. ...[V]oltage tends toward equilibrium ...If you have this ...high voltage [or current] ...stored in a battery ...[T]ake a wire and hook it from one side to the other ...Its going to equalize ...and the batterys going to be dead ..."