Critical Mass: How One Thing Leads to Another

  • Philip Ball
William Heinemann: 2004. 644 pp. £25 To be published by Farrar, Straus and Giroux in the US 0374281254 0434011355 | ISBN: 0-374-28125-4

Psychohistory is a remarkably accurate theory of humans' collective behaviour. It predicts the rise and fall of political movements and empires, and even the sweep of civilization itself. Like the calculations at the root of the insurance industry, it is a fundamentally statistical science, valid only for groups large enough for the vagaries of individuals to average out.

Of course, this theory is the stuff of science fiction, as readers of Isaac Asimov's Foundation series will recognize. But in the past decade or two, the dream of psychohistory — although admittedly in a much more modest form — has seduced a motley crew of physicists, complex-systems theorists and social scientists. Borrowing the tools of statistical mechanics and nonlinear dynamics, and armed with unprecedented computer power and huge data sets, they have re-examined some classic puzzles about human group behaviour and its social, economic and political ramifications. These include the causes of boom–bust cycles in the economy; the long-tailed distribution of wealth; the stampedes of panicked crowds; how altruism can emerge in a group of selfish individuals; and the infuriating waves of congestion that can clog traffic on an otherwise open highway. The goal, in short, is to develop a physics of society.

In his fascinating new book Critical Mass, Philip Ball tells the story of this research in a comprehensive and often captivating way. But what I liked best about the book is that Ball delves far beyond today's headlines. In particular, I was surprised to learn that this intellectual thread has a long history that is the exact reverse of what is generally supposed. Statistical physics did not spawn social physics; it was the other way around.

In the 1870s, when James Clerk Maxwell was developing the kinetic theory of gases, he knew it would be impossible to track the motion of countless particles ricocheting in a hot gas. But he drew hope from an earlier generation of social statisticians, who had demonstrated that enormous populations of people — who were individually every bit as capricious as gas molecules — could nevertheless display precise regularities. After reading Henry Thomas Buckle's History of Civilization in England, which espoused this statistical point of view, Maxwell wrote: “Those uniformities which we observe in our experiments with quantities of matter containing millions and millions of molecules are uniformities of the same kind as those explained by Laplace and wondered at by Buckle arising from the slumping together of multitudes of causes each of which is by no means uniform with the others.”

Even the term ‘statistics’ originated in this movement to quantify social phenomena. In 1749, the German scholar Gottfried Achenwall suggested it as a name for the numerical study of the states of society, which were just beginning to be summarized in terms of death rates, birth rates and other population measures.

Critical Mass is full of historical tidbits like this. Ball particularly enjoys setting the record straight on matters of nomenclature, priority and the like. Thus we learn that Adam Smith argued that a hidden hand, not an invisible one, ruled free markets, and that Maxwell's demon was so named by William Thomson, much to the chagrin of the devoutly religious Maxwell. Maxwell had described his hypothetical creature more lovingly, as “a very observant and neat-figured being”.

This book is impressively clear and breathtaking in scope. Ball explains the basics of every subject he treats, from the political upheavals in seventeenth-century England that gave rise to Thomas Hobbes' vision of utopia, to van der Waals' theory of phase transitions between liquids and gases. Furthermore, unlike so many recent books about complexity theory, this one sets everything in proper historical context, and does not oversell its ideas. Ball even draws on pop literature. For example, to illustrate the abruptness and long-range character of phase transitions, he invokes Kurt Vonnegut's Grand Ah-Whoom from Cat's Cradle, in which a shard of ice-nine seeds the freezing of all the world's oceans.

On the other hand, I did find Ball's treatment of the discovery process a bit disembodied. Or to say that more positively, this is a book about ideas, not about scientists and their struggles. You won't learn much about how the pioneers in this field made their breakthroughs, or about what drove them, or what they were like. But perhaps that would be asking too much. The book is already massive, and its heft made me wonder if its title were a pun.

Speaking of which, the title Critical Mass: How One Thing Leads to Another struck me as uncannily (or perhaps intentionally?) close to the title of Malcolm Gladwell's recent bestseller, The Tipping Point: How Little Things Can Make a Big Difference. Both books deal with collective phenomena in society, or what Gladwell calls social epidemics, but the resemblance ends there. Gladwell's book is fluffy and full of entertaining anecdotes, but is often unconvincing. Ball's is substantial, impeccably researched and generally more persuasive. For anyone who would like to learn about the intellectual ferment at the surprising junction of physics and social science, Critical Mass is the place to start.