Entropy and The Second Law

The Finer Points of Heat

 By 1852, Thomson had come to believe that heat could be both transformed into work, as described by Joule’s theory, and free flowing to produce no work at all, as described by Fourier’s theory. In the latter, heat was simply dissipated, but not lost in accordance with the first law. Moreover, he distinguished between high quality and low quality energy and insisted that the universal tendency for energy is to dissipate as heat, making it unavailable for work. But Thomson wasn’t the only one thinking about the finer points of heat … so was Clausius.
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Entropy, Microstates and Boltzmann

Ludwig Boltzmann‘s Early Career

Ludwig Boltzmann (1844–1906) was born in Vienna and attended the University of Vienna, where he received his doctorate in 1867. Boltzmann was a restless spirit, changing (by choice) from one academic position to another, a total of seven times in his almost forty-year career.

From the early 1870s on, Boltzmann was a scientific superstar and very much in demand. To get Boltzmann to accept a professorship of theoretical physics at the University of Vienna in 1894, the Austrian minister of culture had to offer him the highest salary then paid to any Austrian university professor. Boltzmann had already been a professor at the university of Vienna twice before, once from 1867–1869 as an assistant professor, and a second time from 1873–1876 as a professor of mathematics. Nonetheless, in 1900 he left for a third time.

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The Universal Tendency of Energy

William Thomson’s Struggle with Heat and Work

In 1847, when William Thomson (later Lord Kelvin) (1824–1907) learned of Joule’s experiments (on the mechanical equivalent of heat) demonstrating that work could be converted to heat, he immediately recognized the impact of this discovery. Moreover, it was clear, although not explicitly demonstrated by Joule’s experiments (but nonetheless claimed by Joule), that this equivalence meant that one would expect the conversion of heat into work to be possible as well. This caused problems for Thomson, since at that time, he was still a proponent of caloric theory, which stood in direct opposition to Joule’s conclusion.

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Entropy and Atoms

Our understanding of the connection between entropy and the microscopic world of atoms is mostly due to the work of James Clerk Maxwell and Ludwig Boltzmann.

Energy and Entropy

Energy and the first law that governs it can’t explain why certain processes tend in what apparently is a favored direction; for that we need entropy.

Clausius Discovers Entropy

Clausius formulated much of the original ideas of his theory on entropy in 1854. However, it wasn’t until 1865 that he actually named his new property “entropy”.

Energy, Entropy and the Universe

Whereas the universe keeps energy at a constant (energy is conserved), it continues to increase the entropy. Therefore, no process that occurs will ever result in an overall decrease in the entropy of the universe. The universes’ tendency of maximizing entropy is reminiscent of “a universal tendency to the dissipation of mechanical energy” as stated by Thomson, and Clausius noted the connection.