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Critical Mass: How One Thing Leads to Another

Philip Ball

posted on 16 July 2007

reviewed by Joseph Wakeling

What does physics have to say about the workings of society? Quite a lot, most readers of Econophysics Forum will probably agree, but I suspect even here most will be surprised at how much Philip Ball has squeezed into the pages of a paperback book. From multi-agent modelling, crowd and traffic dynamics, financial markets and networks to the development and growth of firms, war, crime, politics and the spread of culture, Critical Mass is a remarkable survey of an ever-growing field, that mixes fine storytelling and a deft feel for interesting social phenomena with elegant descriptions of the various theories proposed to explain them.

While clearly aimed at a popular audience, professionals will still find much to treasure. Interdisciplinary scientists inevitably need friendly introductions to their colleagues’ fields and the particular delight of this book is that it serves the needs of both sides. Physicists, who can sometimes have quite a narrow sense of the social and economic literature, will appreciate the window opened onto the rich tapestry of thought that informs these fields. Ball rightly recognises the importance of creative and questioning study even as he critiques methodology, rigour or conclusions — crediting Marx, for example, for his observation of the endogenous nature of market fluctuations, or Gary Becker for his recognition of the economic and self-interested aspects of social conventions such as marriage and family life. He does not shy away, where appropriate, from criticising the aspects of econophysical culture that help keep the field on the outskirts of economics, criticisms that — like the recent article on “Worrying trends in econophysics” — should be carefully considered by the community.

For readers coming from social or economic backgrounds, Ball provides an excellent introduction to physics-based concepts and techniques, conveying a strong sense of the theories and phenomena described — statistical mechanics, phase transitions, symmetry breaking — without recourse to complicated or unfamiliar mathematics (a point I suspect physicists will themselves appreciate). The development of many of these ideas alongside corresponding social phenomena — diffusion-limited aggregation compared to city growth, spin-glasses and energy landscapes compared to the formation of social or national coalitions — means that members of both communities gain a sense of the potential and actual points of collaboration between their disciplines.

There are inevitably some niggles. Specialists in any given area will probably wish there had been just a few more details on the finer points of their topic (inevitable, given that whole books can be written on subjects Ball addresses in a chapter or two); physicists may also wish that more attention was paid to the difference between models whose behaviour can be rigorously understood, such as the Ising model or the Minority Game, and looser multi-agent simulations where the range of parameters may mean it is difficult to precisely understand what influences what. Ball repeats the unfortunate fallacy it is relevant that self-organized criticality is not observed in real sandpiles when Bak, Tang and Wiesenfeld never claimed it would be, and I felt rather sorry for Serge Galam who, despite a considerable amount of effort to try to bring physics techniques to sociology, is mentioned only in passing in a footnote. It would have been nice, as well, to have some more extended discussion of the internal conflicts and contradictions in neoclassical economic theory which necessitate alternative theoretical approaches (see e.g. Hahn, “The next hundred years”), although to be fair this is amply discussed in other books (Ormerod, Keen) and at this point in time Ball's more conciliatory approach may be more important to bring to the attention of both economists and physicists alike.

Ball never shies away from the limitations of our understanding, both past and present, but ultimately Critical Mass is a book full of hope and encouragement, giving a sense of what has been achieved as well as a feeling of excitement at the unconquered territory that lies ahead — and perhaps its most hopeful message is in the opening chapters, in the history that precedes us. Physics, Ball reveals, has been an influence on social and political thought from its earliest days — Thomas Hobbes, whose Leviathan (1651) has been a reference point for virtually all political philosophy since, was strongly influenced by the emerging field and even travelled to Italy to meet the ageing Galileo. But the influence has spread the other way too. It was economic and political research, gathering figures on socioeconomic activity, that discovered striking regularities in the data whose study led to the mathematical field of statistics. Maxwell and Boltzmann’s later application of these methods to thermodynamic phenomena was inspired in no small part by their successful use in social science. It is a beautiful moment. Econophysicists have long claimed that not only can they can do good social and economic science but that studying society will lead to the discovery of new physics as well. Ball's book shows that not only is this possible but that it has already happened at a deep and fundamental level.

Fribourg, 16.07.2007