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einstein's fridge

27 july 2021

Einstein's Fridge maybe isn't the ideal title for a book about thermodynamics. Alternative titles for Paul Sen's new book probably got blocked by Marketing, though. Boltzmann's Fridge sounds like a magical-realist epic. Kelvin's Fridge looks like a typo for Kevin's Fridge, a rom-com about a lonely young guy in Manhattan. And Clausius' Fridge is unpronounceable. No, a popular-science book with Fridge in the title has to be either Einstein's Fridge or Darwin's Fridge.

Einstein won out; as Sen observes, Einstein became "the public face of science" (159) when he was quite young, and still is, long after his death. But Darwin makes an appearance earlier in the book. Neither of them could avoid thermodynamics. Thermodynamics, after all, is the Law.

Einstein also developed an actual fridge. Collaborating with the indomitable Leo Szilard, Albert Einstein took out several refrigerator patents in the 1920s. At one point the pair thought they could revolutionize home fridges by having them run on constantly flowing methanol, flushed out of the system with tap water. Apparently Einstein & Szilard's fridge worked pretty well if you had access to unlimited methanol and vigorous, unstinting water pressure. Most people in the 1920s did not.

Such Gyro Gearloose stuff seems incidental to the famous laws of thermodynamics, though, the first two of which are the simplest and scariest: "the energy of the universe is constant"; "the entropy of the universe tends to increase" (257). But refrigerators come up often in thinking about thermodynamics, because they reverse the process of entropy. Leave cold beer out at room temperature and it will always come to room temperature; that's entropy. Room-temperature beer will never get cold unless you put it in the fridge; that's the Law. The fridge doesn't break the Law; it gets around it, using an external source of energy in the service of cold beer.

For such giants as Lord Kelvin, refrigerators were abstract things, but Sen shows that a great deal of the theoretical physics of the 19th century arose from engineering problems that were extremely mundane. Beer was a factor. James Joule, who established the link between heat and work that we now think of abstractly as energy itself, was a professional brewer with a practical interest in improving his company's machines. Kelvin himself, back when he was plain William Thomson, collaborated with his brother James, who worked refining ship engines.

Thermodynamics and associated principles – the impossibility of perpetual motion, the arrow of time – are quite intuitive ideas. They sound obvious now, but Sen conveys very sharply the degree of controversy that insights into thermodynamics met with in the 19th century. Ludwig Boltzmann conceived of a universe that tends toward the disorder and featurelessness of entropy, because so many states of featureless disorder exist compared to neatly-organized ones and the odds are always in favor of the disordered ones. In Boltzmann's lifetime critics as illustrious as Ernst Mach and Max Planck attacked his ideas, in part because Boltzmann grounded his work in statistics and inferred the existence of atoms and molecules that nobody could see. Boltzmann ended up hanging himself. Of course, he might have hanged himself if he'd been a brewer instead of a theoretical physicist. But his peers' constant carping about his theories can't have fostered his mental health.

Einstein's Fridge is a series of miniature narratives of genius, strung on the thread of thermodynamics. The more interesting stories, to me, are the earlier ones – possibly just because I knew so much less about them than even the very little I know about 20th-century developments. Figures like Sadi Carnot and Josiah Gibbs aren't the public face of science, for sure, but Sen does good work here recuperating their significance for the lay reader.

After the century turns we get quite a bit about relativity and gravity (this being an Einstein book after all); about Claude Shannon and information; about Alan Turing (though less about Turing's codebreaking and computing, though they're included than about Turing's ideas on how entropy can reverse itself as embryos develop, building highly-organized structures out of blobs); about Stephen Hawking (and Jacob Bekenstein) and black holes.

At times Sen's descriptions of thought (and real) experiments defeat me. That's truly on me. I am slow to visualize the terms of word problems and easily defeated by inverting a drawing. When discussing steam engines (3, 13), for instance, Sen reverses the direction of a piston between diagrams, deliberately mentioning the reversal as if this were a bagatelle for the reader to deal with; but he lost me permanently on page 13 by not keeping his ideal machines running in the same direction.

Sen, Paul. Einstein's Fridge: How the difference between hot and cold explains the universe. New York: Scribner [Simon & Schuster], 2021.