Opinion – Marcelo Viana: D’Alembert, mathematician and Enlightenment thinker

Frenchman Jean Le Rond d’Alembert (1717–1783) is one of the most brilliant thinkers of the Enlightenment. Mathematician, physicist and philosopher, he also made important contributions to astronomy: he was the first to explain the phenomenon of the precession of the equinoxes from Newton’s laws through precise calculations. One of the craters on the Moon is named after him.

His interest in music led him to discover the wave equation, the mathematical formula that describes vibrating bodies, like guitar strings. This discovery created a new area of ​​mathematics, the theory of partial differential equations, one of the most important until today.

Another very important contribution is D’Alembert’s Theorem, also called Fundamental Theorem of Algebra: every polynomial equation of degree N has exactly N solutions in the set of complex numbers. Calculus students are also familiar with D’Alembert’s criterion for the convergence of infinite series.

In physics, in addition to the development of wave theory, his main contribution was the publication of the “Treatise on Dynamics”, a fundamental step in the mathematical formalization of Newton’s ideas, precursor of the works of Lagrange and Laplace. At the base is the so-called d’Alembert Equilibrium Principle, also well known to graduate students.

Outside the scientific world d’Alembert is best known for having been, with Denis Diderot, co-editor of the “Encyclopedia”, an ambitious initiative to collect the knowledge of the time and make it accessible to all. D’Alembert brought this great project, a symbol of the Enlightenment, to life from the beginning until 1757, when he fell out with Diderot.

And yet, the beginning of his life could not have been less promising. Born from a temporary relationship between his mother, Claudine de Tencin, and an aristocrat, possibly the knight Louis-Camus Destouches, he was abandoned the day after giving birth on the stairs of the chapel Saint-Jean-le-Rond (after whom he was named). .

Recovered by the father, it was handed over to the Hospice for Found Children and, later, to an adoption family. Destouches left him a small annual income in his will, which ensured his survival and allowed him to carry out his studies.

In 1772, D’Alembert became perpetual secretary of the French Academy of Sciences. Nowadays, it is a position with fixed mandates –the current holder is the mathematician Étienne Ghys, a great friend of Brazil–, but at the time the name was taken seriously: D’Alembert stayed in the position until he died.

As the abbot of Saint-Germain l’Auxerrois refused to bury an avowed atheist in his church, his body was accompanied by a long procession to the Cemetery des Porcherons (later deactivated), where he was buried in a mass grave.