Historical context
The term entropy was coined in 1865 by the German physicist Rudolf Clausius (1822–1888), who derived it from the Greek tropé (transformation). Clausius summarised the two laws of thermodynamics in a now-famous sentence: “The energy of the universe is constant; the entropy of the universe tends to a maximum” (Simonyi 2012, ch. 4).
This sentence condenses the whole chapter into a single line: the first law (energy is conserved) and the second law (entropy increases). The phrase “tends to a maximum” already contains the unsettling idea of the heat death of the universe, a final state of maximum entropy in which no useful transformation would be possible any longer.
It was Ludwig Boltzmann (1844–1906) who gave entropy a microscopic meaning with the formula , which today bears his name and is engraved on his tomb in the Zentralfriedhof in Vienna. His probabilistic interpretation — the idea that the laws of thermodynamics are statistical and that entropy counts microstates — was opposed for decades by supporters of energetics (Ernst Mach, Wilhelm Ostwald), who went so far as to reject the very existence of atoms.
At the 1895 Lübeck conference the clash between Boltzmann and Ostwald was described by the young Sommerfeld as a fight between a bull and a nimble matador, but this time the matador was losing (Simonyi 2012, pp. 381–386). Boltzmann, depressed and partly worn down by this opposition, took his own life in 1906 at Duino, near Trieste, just a few years before Jean Perrin’s experiments on Brownian motion (1908) definitively confirmed the existence of atoms (Brandt 2009, ch. 5) — vindicating, too late, the man who had built that theory.
For the works cited see Riferimenti bibliografici.
Links
Topics: Entropy and the second law Concepts: Entropy · Second law of thermodynamics
Related exercises: Worked exercise — the coffee cools down · Hot shower: ΔS of the universe · Heat from hot to cold: proof