Einstein's Fridge - Paul Sen ****

In Einstein's Fridge (interesting factoid: this is at least the third popular science book to be named after Einstein's not particularly exciting refrigerator), Paul Sen has taken on a scary challenge. As Jim Al-Khalili made clear in his excellent The World According to Physics, our physical understanding of reality rests on three pillars: relativity, quantum theory and thermodynamics. But there is no doubt that the third of these, the topic of Sen's book, is a hard sell.

While it's true that these are the three pillars of physics, from the point of view of making interesting popular science, the first two might be considered pillars of gold and platinum, while the third is a pillar of salt. Relativity and quantum theory are very much of the twentieth century. They are exciting and sometimes downright weird and wonderful. Thermodynamics, by contrast, has a very Victorian feel and, well, is uninspiring. Luckily, though, thermodynamics is important enough, lying behind everything from engines and life to the arrow of time, decay and the future of the universe that in the right hands it can still be made interesting, and Sen does this well by hanging his narrative on the lives of the key characters in the history of our understanding of thermodynamics.

Some historians of science (and some scientists) get distinctly sniffy about the 'heroes of science' approach, pointing out how much every scientist builds on the work of others, and (particularly these days) science is hugely collaborative, so picking out individuals can be historically inaccurate. But to complain about this is to fail to understand how storytelling works. We need characters that we can get our heads around. Namecheck everyone and you end up with a bureaucratic document, not an engaging narrative. A good science writer like Sen can focus in on key characters without overdoing the lone genius concept.

Inevitably, we find out a lot about heat and the development of ideas on this, but by far the most interesting aspect of thermodynamics is entropy, and the book is good at explaining this and putting it into context. I think Sen stretches the thermodynamics label more than a little - applying it, for example, to Einstein's short paper extending the special theory of relativity to bring in his famous E=mc² equation, but this is forgivable.

I have a couple of issues. One is the title. Einstein's fridge is very much a bit part player here. Dragging Einstein into the title does a disservice to the greats of thermodynamics. (The word 'thermodynamics' doesn't even appear on the cover.) I also felt at one point that Sen's narrative structure was pushed too far from reality to try to establish a neat storyline. At the end of the chapter on the wonderful James Clerk Maxwell's work on statistical mechanics, Sen claims that despite his work, Maxwell and his contemporaries 'could say why a cup of tea felt hot, but not why, when left to its own devices, it cooled down'. He does this to then be able to introduce Boltzmann's work. But in taking this line Sen assigns a naivety to Maxwell that is unfair. Sen even resorts to breaking his timeline to move Maxwell's demon later in the book, even though it would have been impossible for Maxwell to develop the concept without having a perfectly good idea of how heat is transferred from hot to cold bodies.

This may have caused me a raised eyebrow, but it didn't stop me enjoying the book. Sen has given thermodynamics the importance it deserves, along the way introducing us to some fascinating people and detail of their lives and work. Hot stuff, even if it will eventually cool to ambient temperature.

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Review by Brian Clegg