Numbers that predict revolutions

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http://www.newscientist.com/article/mg21528781.800-calculated-violence-numbers-that-predict-revolutions.html?full=true

PETER TURCHIN thinks he can see the future. Unlike the fortune teller you might find at a seaside carnival, he needs no crystal ball. Instead, the tools of his trade are mathematics and testable theories. Armed with these, his goal is nothing less than to revolutionise the study of history, turning it from a mass of anecdotes into a rigorous, predictive science.

Reasoning that the fate of an empire rests ultimately on social cohesion, he has used historical records to track the prevalence of what he calls collective violence - deaths due to political assassinations, riots and civil wars, but not international wars or ordinary crimes - in three major civilisations, the Roman Republic, medieval Europe and Tsarist Russia. Applying mathematical tools borrowed from population biology, he has found that in each case deaths from collective violence follow two superimposed cycles, one spanning two to three centuries and the other about 50 years (Secular Cycles, Princeton University Press, 2009). What's more, he thinks his data provide enough leverage to understand what drives the longer cycle.

The likeliest explanation, he says, is an idea known as demographic-structural theory, proposed two decades ago by Jack Goldstone at George Mason University in Arlington, Virginia. This argues that in a prosperous culture, population growth or advancing technology eventually leads to an oversupply of labour. That is good news for an expanding upper class who can more easily exploit an increasingly desperate labour force. Eventually, though, the society becomes so top-heavy that even some members of the elite can no longer afford the good life. Factionalism sets in as the upper classes fight among themselves, social cohesion declines, and the state begins to lose control of its citizens. Then, and only then, does widespread violence break out. Anarchy reigns until enough people fall out of the elite classes, at which point growth and prosperity can return.