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No. 2101:

Today, least action and a flattened Earth. The University of Houston's College of Engineering presents this series about the machines that make our civilization run, and the people whose ingenuity created them.

Pierre-Louis de Maupertuis was a puzzle -- so pure a creature of the Age of Enlightenment that he almost mocks himself. Born in 1698, doted upon by his mother, he went to school in Paris. After studying both music and mathematics, he settled on math.

Maupertuis was brilliant, social, combative, and he ran with all the major early 18th century thinkers. At thirty, he visited London and came back, an ardent Newtonian. His writings on Newton attracted Voltaire's attention -- and that of Voltaire's mistress Emilie du Châtelet who translated the Principia into French. Through them, Maupertuis helped to sell the French on Newton.

Maupertuis was fascinated with one of Newton's ideas in particular, that Earth is not a perfect sphere but slightly flattened at its poles. In 1735, France sent one expedition to Peru and another (that included Maupertuis) to Lapland. The two crews made delicate measurements that correctly suggested Newton was right. 

But Maupertuis became increasingly aggressive as other philosophers attacked the idea that Earth wasn't perfectly round. Voltaire was one of his few supporters, and even Voltaire tended to ridicule his excessive rhetoric. And Maupertuis' grandest rhetoric was yet to come: 1746 found him working on "metaphysical mechanics" in Berlin. There he formulated his Principle of Least Action. It doesn't sound very excessive on the face of it: 

In all changes that take place in the universe, the sum of products of the speed of each body and the distance it moves is the least possible.

That meant, for example, that if you throw a rock, it'll find the most economical path back to earth -- that you can calculate its path by applying his principle. In fact, his Principle of Least Action actually gave the same result as Newton's mechanics. Like other revolutionary ideas, it was more than it first seemed. 

But Maupertuis never doubted that he was on to something big. He titled his paper, The laws of motion and rest deduced from the attributes of God. Then, in an odd inversion of that notion, he claimed to've constructed a proof for the existence of God. 

As anti-Newton German philosophers turned on him, his anger and disillusion led to one alienation after another. He spent the rest of his years trying to apply the Principle of Least Action to explain biology, and life itself. He finally died -- sick, old beyond his years, and separated from home by the Seven Years War.

On some levels, his Principle was almost too basic. The idea that the simplest explanation is the truest, is one we constantly rediscover. But when the Principle was used in straightforward calculations, it solved real problems. Maupertuis had even used an early version to explain refraction by showing that light finds its most rapid path. And, his final vindication came in the 20th century, when DeBroglie used it to show, not the existence of God, but the quantum wavelength of a particle.

I'm John Lienhard, at the University of Houston, where we're interested in the way inventive minds work.

(Theme music)

B. Glass, Maupertuis, Pierre Louis Moreau de, C. C. Gillispie, ed., Dictionary of Scientific Biography, Vol. 9 (New York: Charles Scribner's Sons, 1974).

M. Terrall, The Man Who Flattened the Earth: Maupertuis and the Sciences of the Enlightenment. (Chicago: The University of Chicago Press, 2002).

C. L. Tien and J. H. Lienhard, Statistical Thermodynamics. Revised Printing (Washington, DC: Hemisphere Publishing Corp. 1971/1979): pg. 97.

Maupertuis's Lapland adventure has been celebrated in both French and Finnish stamps:

French Maupertuis stamp

Finnish Maupertuis Stamp