Louis de Broglie

French physicist

• Born: August 15, 1892; Dieppe, France
• Died: March 19, 1987; Louveciennes, France

Through his theory of the wave-particle duality of matter, Louis de Broglie introduced a major and necessary component to quantum theory. For his contributions to the field, de Broglie was awarded the Nobel Prize in Physics in 1929.

Primary field: Physics

Specialties: Theoretical physics; quantum physics

Early Life

Louis de Broglie (lwee deh broh-GLEE) was born August 15, 1892, in Dieppe, France. As the head of an aristocratic family, his father held the title of duc (or duke). Both de Broglie and his brother, Maurice, took an active interest in science; Maurice eventually converted a room in the family estate into a laboratory. De Broglie attended the Lycée Janson-de-Sailly in Paris, where he studied history. He continued to pursue this interest in history at the Sorbonne in the University of Paris, from which he earned his bachelor’s degree in 1910.

De Broglie eventually became drawn to both theoretical physics and the philosophy of science. While his brother played a role in this shift of interest, de Broglie also stated that the works of French mathematician Henri Poincaré were decisive in changing his mind. After three years of intensive work, de Broglie earned a science degree from the University of Paris.

Following the outbreak of World War I in 1914, de Broglie was drafted into military service. He was stationed at the Eiffel Tower in Paris, working as a wireless operator. After the war ended in 1918, de Broglie continued his study of physics in his brother’s private laboratory. During this time, Maurice was studying the nature of charged particles in an electric field; he found that small particles became charged when exposed to X-rays. De Broglie and his brother shared an interest in the nature of the atom, and their experimental work would prove beneficial to de Broglie’s later research.

Life’s Work

As a theoretical physicist, de Broglie’s contribution to science was to provide a different way of thinking about physical phenomena. Unlike experimental scientists, who can demonstrate their results, de Broglie analyzed the research and findings of other physicists and provided a new interpretation of the physical world.

By the end of the nineteenth century, classical physics, which explained physical activity as the interaction between discrete particles of matter or as wave activity, seemed to have answered all the significant problems of physics. One problem, which was first posed in 1900, involved the exchange of energy between electrons and the walls of a container that enclosed the radiation. German physicist Max Planck discovered that these exchanges occurred in bursts of energy rather than a continuous flow of energy. This marked the beginning of the theory of quantum mechanics, a theory that states that electromagnetic waves come in discrete units of energy rather than one continuous flow of wave action.

As an idea, quantum theory violates one of the most rigorously established notions of physics: that light, or radiation, as a wave spreads in a continuous and unbroken manner throughout space. This difference marks the dividing line between classical physics and the modern field of quantum mechanics. For the next quarter of a century, there would be vigorous and bitter debate between physicists who held the classical view and those who began to shift to the quantum description of the universe. Even Planck was not convinced that his own discovery was a conceptual break of such magnitude.

Two years after De Broglie’s discharge from the army and return to the family estate, he joined his brother in conducting X-ray research. Their work dealt with the spectrum of electrons released by X-rays at given frequencies and was directly related to the new model of the atom developed by Danish physicist Niels Bohr. By 1924, the brothers became intrigued by a discovery made by American physicist Arthur Holly Compton. When a quantum of light, which Compton called a “photon,” struck an electron, the photon would lose some of its energy and become a light wave of longer wavelength. Thus, the light photon acted more like a particle than a wave. Based on the work of these scientists and others, de Broglie proposed his hypothesis: Waves can act like particles and particles can act like waves, and this wave-particle duality applies to matter as well as light.

In 1924, de Broglie presented this analysis in his doctoral dissertation, entitled Recherches sur la théorie des quanta (Research on the quantum theory). The faculty of the University of Paris viewed his idea with skepticism, as there was no experimental evidence to support his view. With the support and encouragement of German-born physicist Albert Einstein, however, de Broglie was awarded his degree and went on to publish his work. Einstein also actively began to promote this analysis among other physicists. Austrian-born physicist Erwin Schrödinger used this idea of the dual nature of matter to develop a theory of wave mechanics. By the late 1920s, American physicist Clinton Davisson and English physicist Sir George Paget Thomson, working independently, were able to demonstrate that electrons could be bent, focused, and diffracted like waves. As a result of this experimental confirmation and for his contribution to quantum mechanics, de Broglie was awarded the Nobel Prize in Physics in 1929.

For several years, de Broglie continued this line of research while looking for a foundation of quantum mechanics based on classical physics. In 1933, he was elected a member of the French Academy of Sciences, and in 1945 he served with his brother as a counselor to the French High Commission on Atomic Energy. Upon the death of his brother in 1960, he assumed the family title, becoming the seventh duke of Broglie. De Broglie died in Louveciennes, France, on March 19, 1987.

Impact

There were two breakthroughs in physics at the beginning of the twentieth century: the theory of relativity and the theory of quantum mechanics. While the term “relativity” has entered the general vocabulary, quantum mechanics remains obscure to the general public. Yet, many scientists in disciplines such as chemistry, astronomy, and biology regularly use quantum theory in their daily work. De Broglie was able to join a number of perplexing and anomalous experiments and theories into a single insight into the nature of the physical universe. Waves are part of every moving physical object, such as a thrown baseball. The wavelength of a moving baseball is insignificant compared to the size of the ball, yet the wavelength of an electron is significant when compared to its size and results in a wave-particle duality. By bringing together wave and particle, de Broglie helped to produce a fundamental change in the way scientists understood the physical world.

In recognition of his work, de Broglie was awarded a number of prestigious prizes, including the first Henri Poincaré Medal of the French Academy of Sciences (1929) and the Grand Prize of the Society of Engineers of France (1952). He held honorary degrees from a number of universities and was a member of many scientific societies, including the Royal Society of London, the US National Academy of Sciences, and the American Academy of Arts and Sciences.

Bibliography

Broglie, Louis de. Matter and Light: The New Physics. Translated by W. H. Johnston. New York: Dover, 1946. Print. Explains de Broglie’s theories regarding the wave-particle duality of light and matter.

Segrè, Emilio. From X-Rays to Quarks: Modern Physicists and Their Discoveries. Reprint. New York: Dover, 2007. Print. Explores the effects of de Broglie’s discoveries on the development of quantum theory and physics as a whole.

Whitaker, Andrew. The New Quantum Age: From Bell’s Theorem to Quantum Computation and Teleportation. Oxford: Oxford UP, 2012. Print. Discusses the development of the field of quantum mechanics and places de Broglie’s research in historical and scientific context.