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One cannot speak of Emilie’s accomplishments in science and mathematics without speaking of Voltaire. Emilie first met Voltaire when she was a child, as he was one of the many dinner guests at her parent’s home. When Emilie was 27 they met again and developed a strong relationship.

Voltaire had just returned from England and Emilie was one of few women with whom he could discuss his interests in political, philosophical, and most importantly, science. In addition, they both held deep convictions about Newton’s world view, which at that time, was quite unpopular in France. Fleeing a warrant for his arrest (for his anti-French writings), Voltaire took up residence at du Chatelet’s husband’s home– Cirey-sur-Blaise in northeastern France. It was here at Cirey where du Chatelet completed some of her most significant work.

Of this time Voltaire wrote, “found in 1733 a young lady who felt more or less as I did, and who resolved to spend several years in the country to cultivate her mind, far from the tumult of the world. It was the marquise Du Châtelet, the woman who in all France had the greatest disposition for all the sciences. … Seldom has so fine a mind and so much taste been united with so much ardour for learning; but she also loved the world and all the amusements of her age and sex. Nevertheless she left all this to go and bury herself in a dilapidated house on the frontiers of Champagne and Lorraine, where the land was very fertile and very ugly. She beautified the house, to which she added pleasant gardens. I built a gallery, in which I created a very fine collection of scientific instruments. We had a large library.” (L Morland (ed.), Voltaire, Oeuvres complètes (1879) from O’Connor and Robertson Chatelet Biography, para. 14). The library that they created was as well stocked as that of the Academy of Sciences in Paris and they brought in the latest laboratory equipment from England.

By 1736 Voltaire and du Chatelet were jointly working on the book, Eléments de la philosophie de Newton. The book was published in 1738 under Voltaire’s name, but in the preface he makes it clear that the book was a collaborative process with Emilie.

With Voltaire being much older than du Chatelet, one might think that she was simply the female assistant, or young lover, but that was not the case. Emilie was a formidable partner to Voltaire and was challenging some of the days most important scientific assumptions.

One of those assumptions was the understanding of what energy was. At that time, it was commonly held that energy was simply the product of its mass times its velocity (e = mv)—that is to say that if a 10 pound object is going 12 miles per hour it would have 120 units of energy. Even Voltaire himself had popularized this idea, originally from Newton. But, Emilie knew of a different and competing theory on the subject written by the German philosopher and mathematician, Gottfried Leibniz. Then, du Chatelet found compelling evidence in some experiments the Dutch researcher, Willem Gravesande, had been conducting.  “If the simple E = mv was true, then a weight going twice as fast as an earlier one would sink in twice as deeply. One going three times as fast would sink three times as deep. But that’s not what Gravesande found. If a small brass sphere was sent down twice as fast as before, it pushed four times as far into the clay. It if was flung down three times as fast, it sank nine times as far into the clay.” (NOVA site, 2005, para. 9).

What du Chatelet then did was to revisit Leibniz’s theory and take it to the next level with the scientific evidence as provided by Gravesande’s experiments. The conclusion it led her to was that energy was equal to an object’s mass times it’s velocity squared (E = mv²). This discovery was used by numerous physicists as a way to predict an objects energy. Much, much later, a young scientist, named Albert Einstein would use this discovery as one of the keys that would unlock his theory of relativity, E = mc².

Emilie du Chatelet—Female Scientist