Heat Death

Simon Schaffer

  • Ludwig Boltzmann: The Man who Trusted Atoms by Carlo Cercignani
    Oxford, 329 pp, £29.50, September 1998, ISBN 0 19 850154 4

The Second Law of Thermodynamics has an oddly talismanic status in the public life of physics. Flanders and Swann wrote a song about it; C.P. Snow lectured on it. Whether it refers to the impossibility in a sealed system of letting heat flow from a cooler to a hotter body, or to the tendency of the universe to run down to more chaotic and disorderly states, it forms a key element in the magnificent edifice of the science of heat and energy constructed in the closing decades of the 19th century. Snow apparently thought it fairly easy to describe, and in a strange version of the humiliation game reckoned that to confess ignorance of the Second Law was like an admission that one had never read Shakespeare. His literary dinner companions’ response was suitably thermodynamic – ‘cold and negative’ – convincing him that they were all fatally and stupidly antiscientific.

This was not a new complaint. Snow’s remarks appeared in the Rede Lecture he gave at Cambridge in 1959: back in 1873, a Rede lecturer had already been warned not ‘to speak familiarly of a second law of thermodynamics, as of a thing known for some years to men of culture, who have never even heard of a first law’. For an unproblematic description of this law is neither easy nor straightforward. Ludwig Boltzmann, the greatest physicist of the Austro-Hungarian Empire, spent most of his career trying to define its meaning and clarify its basis. Now Carlo Cercignani, a mathematical physicist working in Milan, tries to explain the importance of Boltzmann’s search and to link it, somehow, to his extraordinary life. ‘The most important thing in a literary work is to give it the right title,’ Boltzmann told Viennese philosophers in 1905. Cercignani’s subtitle refers to trust, but this biography is not a story in which trust seems to play an important role. Instead, it offers a window onto the remarkable battles between self-confident scientific dogmas which raged across Europe at the end of the 19th century – and which continue today.

When professional scientists write books about past heroes, they often have a contemporary aim in view. Cercignani is no exception. He is an expert in rarefied gas dynamics, a science which describes the behaviour of vast arrays of very small particles moving and interacting relatively freely. He has shown how kinetics and heat theory can be used to understand the way in which space vehicles move, not to mention fashionable environmental concerns such as ozone holes, radioactive emissions, aerosols and carbon fibres. Any picture of such particle systems needs the tools of probability and statistics, since, as physicists of the last century began to realise, if you cannot follow the path of each and every particle, you have to judge the chances of any of a vast number of such particles possessing a given energy, or velocity, or position.

Getting Boltzmann right still matters, because the science he helped develop continues to have immense practical value, and, even more important, because there’s no easy consensus about what this science looks like. Cercignani begins by declaring that ‘a good understanding of the Second Law is related to understanding how life is possible,’ because living beings keep going by preserving their good order, struggling against the universal tendency to dissipation and chaos. It is just this struggle which the Second Law is supposed to describe. On the other hand, Cercignani’s book is also a brave attempt to understand the Law through an understanding of Boltzmann’s life of struggle; and, at the same time, it is an account of the problems which arise whenever a scientist tries to appeal to the general public for support, understanding or attention.

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