Pierre Curie

Pierre Curie: The Quiet Half of the Most Famous Marriage in Science

On 19 April 1906, in rain on the Rue Dauphine near the Quai de Conti, a forty-six-year-old physicist slipped beneath a heavy horse-drawn cart and a wheel crushed his skull. He died instantly. Three years earlier he had shared a Nobel Prize; at some point before that he had deliberately burned his own arm with radium to find out what it would do to living tissue. His notebooks are still radioactive, kept in lead-lined boxes at the Bibliothèque nationale de France, which is one way of measuring how close he stood to the thing he discovered.

An Education Without a Schoolroom

He was born in Paris on 15 May 1859, the son of Eugène Curie, a physician of Huguenot descent from Alsace, and Sophie-Claire Depouilly. The medical and freethinking strain ran deep: his grandfather Paul Curie was a doctor and Malthusian humanist, and through his grandmother Augustine Hofer the family traced descent from the mathematician Jean Bernoulli. Pierre was educated at home by his father rather than sent to a lycée, and showed an early, unusual facility for mathematics and — tellingly for what came later — geometry, the science of symmetry.

He took his licence in physics at the University of Paris Faculty of Sciences in 1878, at nineteen, and then did what brilliant men without patrons did in the Third Republic: he worked as a laboratory demonstrator, until 1882, when he took charge of practical work at the School of Physics and Industrial Chemistry. He did not submit his doctorate until 1895, aged thirty-six. For most of his twenties and thirties, in other words, he was a technician who happened to be doing first-rate physics.

The Crystals

In 1880 Pierre and his older brother Jacques demonstrated that squeezing certain crystals generates an electrical potential. They called it piezoelectricity. In 1881 they showed the converse: apply an electric field and the crystal deforms. To measure the effect they built a piezoelectric quartz electrometer, an instrument of exceptional delicacy that would later prove indispensable in a way neither brother could have anticipated.

This is not an obscure curiosity. The piezoelectric effect is why quartz crystal oscillators keep time in essentially every digital circuit made since. The Curie brothers found it while they were, respectively, twenty-one and twenty-four.

Symmetry and the Curie Point

Pierre's doctoral work turned to magnetism, and here his geometric instincts paid. He designed a torsion balance of extreme sensitivity to measure magnetic coefficients, then worked through ferromagnetism, paramagnetism and diamagnetism systematically. He established that paramagnetic susceptibility varies inversely with temperature — Curie's law, with its associated Curie constant — and, more consequentially, that every ferromagnetic substance has a critical temperature above which its ferromagnetism simply vanishes. That threshold is the Curie temperature, and it is now used to read the magnetic history of the seafloor in plate tectonics, in hyperthermia treatment, in measuring caffeine, and in inferring the magnetic fields of other worlds.

Underneath both results sat a principle he articulated in general form: a physical effect cannot possess a dissymmetry absent from its cause. He illustrated it with sand sorted in a gravitational field, where the directional arrangement of the grains reflects the asymmetry of the field acting on them. It is one of the more durable pieces of physical reasoning of the nineteenth century, and it is pure Pierre — abstract, geometric, and about what nature is not allowed to do.

Marie

He was introduced to Maria Skłodowska by the physicist Józef Wierusz-Kowalski, and took her into his laboratory as a student. His courtship was conducted in the register of a man who had never courted anyone: "It would be a beautiful thing," he wrote to her, "if we could spend our life near each other, hypnotized by our dreams." She refused him at first. They married on 26 July 1895 — the same year he finally took his doctorate.

From 1895 the two worked together on radioactivity, a word they coined. On 26 December 1898, with M. G. Bémont, they announced the discovery of radium and polonium, isolated by the fractionation of pitchblende under laboratory conditions that were, by every account including their own, appalling. The American Chemical Society's History Division would give that paper a Citation for Chemical Breakthrough Award in 2015, a century and change later.

Pierre's specific contributions to the radioactivity work were characteristically instrumental and physical rather than chemical. Using magnetic fields, he showed that the emissions from radioactive material sorted into three classes — positively charged, negatively charged, and neutral, which we now call alpha, beta and gamma. With his student Albert Laborde he found that radium continuously emits heat, the first identification of nuclear energy as a source. And both Curies deliberately burned themselves with radium to characterise its effect on flesh, which is how radiation therapy began and, eventually, how they both got sick.

Late Recognition

In 1903 the Royal Society invited him to present the work in London, with Lord Kelvin in the audience, and awarded the Curies the Davy Medal. That same year Pierre shared the Nobel Prize in Physics with Marie and Henri Becquerel, making the Curies the first married couple to win one — the start of a family that would collect five. He received the Matteucci Medal in 1904 and, posthumously, the Elliott Cresson Medal in 1909. He was promoted to professor in the Faculty of Sciences in 1900, made titular professor in 1904, and elected to the Academy of Sciences in 1905, the year before he died.

He was an atheist who nonetheless investigated the spiritualist experiments of Charles Richet and Camille Flammarion, attending Eusapia Palladino's Paris séance in June 1905 and taking careful notes — not from credulity, but because he thought unexplained phenomena might bear on the unexplained parts of magnetism.

Why Pierre Is Called a Genius

The quality is a rare pairing: abstract symmetry reasoning coupled to world-class instrument-making, in the same head. Most physicists have one or the other. Pierre's dissymmetry principle is high theory — a constraint on what effects nature can produce from a given cause — and it came from the same man who hand-built a torsion balance and a quartz electrometer sensitive enough to detect currents nobody else could measure. The Curie temperature and Curie's law are named after him because he found them, but the instruments are the deeper tell: he could think about what to look for and then make the thing that could see it.

The counter-case is worth stating honestly, and it is mostly about credit. The piezoelectric discovery was shared with his brother Jacques, and the division of intellectual labour between them is not recoverable. The radioactivity work was Marie's programme — the pitchblende fractionation, the sheer chemical grind, was hers, and Pierre joined a line of inquiry she had opened. He was, by temperament, an absent-minded and unworldly man who spent seventeen years as a demonstrator and lab supervisor before bothering with a doctorate, which cost French physics a good deal of his best years. And he died at forty-six, before any late synthesis. What survives is not a system but a handful of results that turned out to be load-bearing: piezoelectricity, the Curie point, the symmetry principle, the three-way sorting of radiation.

Legacy

In April 1995 Pierre and Marie were moved from a family cemetery to the Panthéon. His name is now a unit of temperature, a law, a constant, and half a dynasty — Irène and Frédéric Joliot-Curie, Ève Curie, Hélène Langevin-Joliot, Pierre Joliot. The quartz oscillator in the device you are reading this on is his too.

Achievements

• Matteucci Medal — 1904
• Davy Medal — 1903
• Nobel Prize in Physics — 1903
• Benjamin Franklin Medal
• Notable work: piezoelectricity
• Notable work: radioactivity
• Held posts at University of Paris
• Educated at Science Faculty of Paris, Sorbonne and homeschooling
• Fields of research: chemistry, crystallography, magnetism and physics