Famously, this equation takes pride of place on his tombstone.īoltzmann's ideas were inadequately recognised in his lifetime, and he took his own life. S = k B ln W implies that entropy quantifies disorder at the molecular level. On first encounter, it seems surprising - and wonderful - that the two definitions are equivalent, given the very different ideas and language involved. Boltzmann's microscopic definition of entropy is S = k B ln W, where k Bis Boltzmann's constant and W is the number of different possible configurations of a system. Statistical mechanics applies Newton's laws and quantum mechanics to molecular interactions. The increase of entropy in a closed system gives time a direction: S 2 > S 1 ⇔ t 2 > t 1.Ī molecular interpretation comes from statistical mechanics, the meta-theory to thermodynamics. Entropy can decrease, and does so in a refrigerator when you turn it on, but that is not a closed system: the fridge motor compresses the refrigerant gas, raising its temperature enough to allow heat to flow out, a process which exports more entropy into the kitchen than that lost by the cooling interior the heat is not 'of itself' passing from cold (inside) to hotter. The Second Law of Thermodynamics says that entropy cannot decrease in a closed system, which is also correctly expressed by comic songsters Flanders and Swann as 'heat cannot of itself pass from one body to a hotter body'. Originally, entropy had no specific relation to order and it had units of energy over temperature, such as J.K −1. This definition comes from thermodynamics, a classical, macroscopic theory, part of whose great power comes from the fact that it is developed without specifying the molecular nature of heat and temperature. But the original definition of entropy is macroscopic, it is the heat transferred in a reversible process divided by the temperature at which the transfer occurs. ![]() Do life or evolution violate the second law of thermodynamics?Īt the molecular level, entropy is related to disorder.Macroscopic disorder has negligible entropy.
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