SOCIAL PHYSICS

Quetelet, who was born in Ghent in 1796, made a major mathematical contribution to society that most Americans today are uncomfortably familiar with, although few people know to blame Quetelet. He invented the Quetelet index for assessing obesity, a measure better known now as the Body Mass Index, or BMI. But he had much greater vision for applying science to society than merely telling people how to know when they were overweight.

As a youth, Quetelet dabbled in painting, poetry, and opera, but his special talent was math, and he earned a math doctorate in 1819 at the University of Ghent. He got a job teaching math in Brussels, where he was soon elected to the Belgian academy of sciences. During the 1820s, Quetelet expanded his interest from math into physics, and in 1823 he traveled to Paris to study astronomy, part of a plan to establish an observatory in Brussels.

Quetelet later wrote some widely read popularizations of astronomy and physics for the general reader. And he often delivered public lectures on science attended by all segments of the public. Quetelet was highly regarded as a teacher and as a person by those who knew him—he was described as amiable and considerate, tactful and modest, but still a rigorous thinker who expressed his views strongly.7

During his stay in Paris, Quetelet took in more than just astronomy. He also learned probability theory from Laplace and met his colleagues Poisson and Fourier, who also had an interest in the statistics of society. Quetelet was himself strongly attracted to the social sciences, and he soon realized that Laplace’s uses of the bell curve to describe social numbers could be dramatically expanded.

Quetelet began to publish papers on the statistical description of society, and in 1835 authored a detailed treatise on what he called social physics8 (or social mechanics), introducing the idea of an “average man” for analyzing social issues. He knew that there is no one average man, but by averaging various aspects of a great many men, much could be learned about society. “In giving to my work the title of Social Physics, I have had no other aim than to



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