Einstein’s Fridge: How the Difference Between Hot and Cold Explains the Universe

Einstein’s Fridge: How the Difference Between Hot and Cold Explains the Universe by Paul Sen

At some point in your schooling you learned the Laws of Thermodynamics. And then, at some point shortly thereafter (or at least, shortly after the test on them), you promptly forgot them. And even if you later in life you kept up with reading about science, well, there was always something sexier to read about: black holes, new particles, rovers zipping around on Mars. But in Einstein’s Fridge: How the Difference Between Hot and Cold Explains the Universe (2021), Paul Sen is here to argue thermodynamics deserves both your attention and your respect, seeing as how it lies at the foundation of just about all our technological advancement. And darn if he doesn’t make the case.

On the one hand, the Laws (Sen really focuses mainly on the first two), are pretty simple to formulate: energy can never be created or destroyed but is always conserved and the entropy of the universe is always increasing. But while the words are simple, learning why those things are true was fiendishly difficult. And explaining it so non-scientists understand it (as any high school physics teacher will attest) isn’t much better. But while it took a host of curious and brilliant people (including well known luminaries like Maxwell, Einstein, Turing, and Hawking) centuries to do the former, Sen takes just over 200 pages to do the latter and do it supremely well.

Sen begins in Britain in the early 1800s with Sadi Carnot, who despite dying tragically at age 36, is known as “the founding father of the science of thermodynamics.” From there, Sen methodically and clearly marches through time and science as one discovery after another furthers human knowledge of heat, entropy, and the basic underpinnings of the universe. It’s also a walk through technological progress, from steam engines to internal combustion engines to that titular home appliance (and yes, Einstein did form a business to design better and safer refrigerators) to the transistor and the silicon computer chip. One of the more interesting aspects of Einstein’s Fridge is how the technological advancements often came prior to understanding the underlying scientific fundamentals, and often raised the questions that provoked study of the basic science that allowed for the technology to work.

The narrative is never anything but crystal clear, with Sen lucidly and carefully laying out the science, aided by a number of greatly appreciated illustrations. He also makes frequent use of analogies to make the unfamiliar and esoteric more familiar and grounded in something easier to understand, a typical tool in popular science books. Here, though, things are a bit of a mixed bag. While many of the analogies helped illuminate their subjects, a few I thought were actually a bit muddy, leaving me wondering if that made things more complicated than simpler. Meanwhile, the thumbnail sketches of the many important figures such as the aforementioned household names, along with others such as Kelvin, Joule, Helmholtz and others are concise but engaging and at times even moving, as with the tragic early death of Carnot, or the suicides of Bernoulli and Turing.

Einstein’s Fridge is wonderfully clear, winningly concise, peppered with interesting personal stories, and leaves you knowing more about its topic than you did going in. Not that you should feel too bad about how little you knew at the start, given that Sen closes with a story of how even Stephen Hawking got thermodynamics wrong. So maybe the rest of us can be forgiven for needing just the book Sen provides us.