Louis de Broglie

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Louis Victor Pierre Raymond, 7th Duc de Broglie (/də ˈbroʊɡli/,^[1] also US: /də broʊˈɡliː, də ˈbrɔɪ/;^[2][3] French: [də bʁɔj]^[4][5] or [də bʁœj]    ^ⓘ; 15 August 1892 – 19 March 1987)^[6] was a French physicist and aristocrat known for his contributions to quantum theory. In his 1924 PhD thesis, he postulated the wave nature of electrons and suggested that all matter has wave properties. This concept is known as the de Broglie hypothesis, an example of wave-particle duality, and forms a central part of the theory of quantum mechanics.

De Broglie won the Nobel Prize in Physics in 1929, after the wave-like behaviour of matter was first experimentally demonstrated in 1927.

The wave-like behaviour of particles discovered by de Broglie was used by Erwin Schrödinger in his formulation of wave mechanics.^[7]: 270  De Broglie's pilot-wave concept,^[8] was presented at the 1927 Solvay Conferences then abandoned, in favor of the quantum mechanics, until 1952 when it was rediscovered and enhanced by David Bohm.^[9]

Louis de Broglie was the sixteenth member elected to occupy seat 1 of the Académie française in 1944, and served as Perpetual Secretary of the French Academy of Sciences.^[10][11] De Broglie became the first high-level scientist to call for establishment of a multi-national laboratory, a proposal that led to the establishment of the European Organization for Nuclear Research (CERN).^[12]

Louis de Broglie belonged to the famous aristocratic family of Broglie, whose representatives for several centuries occupied important military and political posts in France. The father of the future physicist, Louis-Alphonse-Victor, 5th duc de Broglie, was married to Pauline d’Armaille, the granddaughter of the Napoleonic General Philippe Paul, comte de Ségur and his wife, the biographer, Marie Célestine Amélie d'Armaillé. They had five children; in addition to Louis, these were: Albertina (1872–1946), subsequently the Marquise de Luppé; Maurice (1875–1960), subsequently a famous experimental physicist; Philip (1881–1890), who died two years before the birth of Louis, and Pauline, Comtesse de Pange (1888–1972), subsequently a famous writer.^[13]

Louis was born in Dieppe, Seine-Maritime. As the youngest child in the family, Louis grew up in relative loneliness, read a lot, and was fond of history, especially political. From early childhood, he had a good memory and could accurately read an excerpt from a theatrical production or give a complete list of ministers of the Third Republic of France. For this, he was predicted to become a great statesman in the future.^[14]

De Broglie had intended a career in humanities, and received his first degree (licence ès lettres) in history. Afterwards he turned his attention toward mathematics and physics and received a degree (licence ès sciences) in physics. With the outbreak of the First World War in 1914, he offered his services to the army in the development of radio communications.

After graduation, Louis de Broglie joined the engineering forces to undergo compulsory service. It began at Fort Mont Valérien, but soon, on the initiative of his brother, he was seconded to the Wireless Communications Service and worked on the Eiffel Tower, where the radio transmitter was located. Louis de Broglie remained in military service throughout the First World War, dealing with purely technical issues. In particular, together with Léon Brillouin and brother Maurice, he participated in establishing wireless communications with submarines. Louis de Broglie was demobilized in August 1919 with the rank of adjudant. Later, the scientist regretted that he had to spend about six years away from the fundamental problems of science that interested him.^[14][15]

His 1924 thesis Recherches sur la théorie des quanta^[16] (Research on the Theory of the Quanta) introduced his theory of electron waves. This included the wave–particle duality theory of matter, based on the work of Max Planck and Albert Einstein on light. This research culminated in the de Broglie hypothesis stating that any moving particle or object had an associated wave. De Broglie thus created a new field in physics, the mécanique ondulatoire, or wave mechanics, uniting the physics of energy (wave) and matter (particle). He won the Nobel Prize in Physics in 1929 "for his discovery of the wave nature of electrons".^[17]

In his later career, de Broglie worked to develop a causal explanation of wave mechanics, in opposition to the wholly probabilistic models which dominate quantum mechanical theory; it was refined by David Bohm in the 1950s. The theory has since been known as the De Broglie–Bohm theory.

In addition to strictly scientific work, de Broglie thought and wrote about the philosophy of science, including the value of modern scientific discoveries. In 1930 he founded the book series Actualités scientifiques et industrielles published by Éditions Hermann.^[18]

De Broglie became a member of the Académie des sciences in 1933, and was the academy's perpetual secretary from 1942. He was asked to join Le Conseil de l'Union Catholique des Scientifiques Francais, but declined because he was non-religious.^[19][20] In 1941, he was made a member of the National Council of Vichy France.^[21] On 12 October 1944, he was elected to the Académie Française, replacing mathematician Émile Picard. Because of the deaths and imprisonments of Académie members during the occupation and other effects of the war, the Académie was unable to meet the quorum of twenty members for his election; due to the exceptional circumstances, however, his unanimous election by the seventeen members present was accepted. In an event unique in the history of the Académie, he was received as a member by his own brother Maurice, who had been elected in 1934. UNESCO awarded him the first Kalinga Prize in 1952 for his work in popularizing scientific knowledge, and he was elected a Foreign Member of the Royal Society on 23 April 1953.

Louis became the 7th duc de Broglie in 1960 upon the death without heir of his elder brother, Maurice, 6th duc de Broglie, also a physicist.

In 1961, he received the title of Knight of the Grand Cross in the Légion d'honneur. De Broglie was awarded a post as counselor to the French High Commission of Atomic Energy in 1945 for his efforts to bring industry and science closer together. He established a center for applied mechanics at the Henri Poincaré Institute, where research into optics, cybernetics, and atomic energy were carried out. He inspired the formation of the International Academy of Quantum Molecular Science and was an early member.^[22]

Louis never married. When he died on 19 March 1987 in Louveciennes at the age of 94,^[6] he was succeeded as duke by a distant cousin, Victor-François, 8th duc de Broglie. His funeral was held 23 March 1987 at the Church of Saint-Pierre-de-Neuilly.^[23]