Louis de Broglie

Louis Victor de Broglie, a theoretical physicist and member of the French nobility, is best known as the father of wave mechanics, a far-reaching achievement that significantly changed modern physics. For this groundbreaking work, de Broglie was awarded the 1929 Nobel Prize for physics.

Louis Victor Pierre Raymond de Broglie was born on August 15, 1892, in Dieppe, France, to Duc Victor and Pauline d'Armaille Broglie. His father's family was of noble Piedmontese origin and had served French monarchs for centuries, for which it was awarded the hereditary title Ducfrom King Louis XIV in 1740, a title that could be held only by the head of the family. A later de Broglie assisted the Austrian side during the Seven Years War and was awarded the title Prinz for his contribution. This title was subsequently borne by all members of the family. Another of de Broglie's famous ancestors was his great-great-grandmother, the writer Madame de Stael.

The youngest of five children, de Broglie inherited a familial distinction for formidable scholarship. His early education was obtained at home, as befitted a great French family of the time. After the death of his father when de Broglie was fourteen, his eldest brother Maurice arranged for him to obtain his secondary education at the Lycée Janson de Sailly in Paris.

After graduating from the Sorbonne in 1909 with baccalaureates in philosophy and mathematics, de Broglie entered the University of Paris. He studied ancient history, paleography, and law before finding his niche in science, influenced by the writings of French theoretical physicist Jules Henri Poincaré. The work of his brother Maurice, who was then engaged in important, independent experimental research in X rays and radioactivity, also helped to spark de Broglie's interest in theoretical physics, particularly in basic atomic theory. In 1913, he obtained his Licenciéès Sciences from the University of Paris's Faculté des Sciences.

De Broglie's studies were interrupted by the outbreak of World War I, during which he served in the French army. Yet even the war did not take the young scientist away from the country where he would spend his entire life; for its duration, de Broglie served with the French Engineers at the wireless station under the Eiffel Tower. In 1919, after what he considered to be six wasted years in uniform, de Broglie returned to his scientific studies at his brother's laboratory. Here he began his investigations into the nature of matter, inspired by a conundrum that had long been troubling the scientific community: the apparent physical irreconcilability of the experimentally proven dual nature of light. Radiant energy or light had been demonstrated to exhibit properties associated with particles as well as their well-documented wave-like characteristics. De Broglie was inspired to consider whether matter might not also exhibit dual properties. In his brother's laboratory, where the study of very high frequency radiation using spectroscopes was underway, de Broglie was able to bring the problem into sharper focus. In 1924, de Broglie, with over two dozen research papers on electrons, atomic structure, and X rays already to his credit, presented his conclusions in his doctoral thesis at the Sorbonne. Entitled "Investigations into the Quantum Theory," it consolidated three shorter papers he had published the previous year.

In his thesis, de Broglie postulated that all matter—including electrons, the negatively charged particles that orbit an atom's nucleus—behaves as both a particle and a wave. Wave characteristics, however, are detectable only at the atomic level, whereas the classical, ballistic properties of matter are apparent at larger scales. Therefore, rather than the wave and particle characteristics of light and matter being at odds with one another, de Broglie postulated that they were essentially the same behavior observed from different perspectives. Wave mechanics could then explain the behavior of all matter, even at the atomic scale, whereas classical Newtonian mechanics, which continued to accurately account for the behavior of observable matter, merely described a special, general case. Although, according to de Broglie, all objects have "matter waves," these waves are so small in relation to large objects that their effects are not observable and no departure from classical physics is detected. At the atomic level, however, matter waves are relatively larger and their effects become more obvious. De Broglie devised a mathematical formula, the matter wave relation, to summarize his findings.

American physicist Albert Einstein appreciated the significant of de Broglie's theory; de Broglie sent Einstein a copy of his thesis on the advice of his professors at the Sorbonne, who believed themselves not fully qualified to judge it. Einstein immediately pronounced that de Broglie had illuminated one of the secrets of the universe. Austrian physicist Erwin Schrödinger also grasped the implications of de Broglie's work and used it to develop his own theory of wave mechanics, which has since become the foundation of modern physics. Still, many physicists could not make the intellectual leap required to understand what de Broglie was describing.

De Broglie's wave matter theory remained unproven until two separate experiments conclusively demonstrated the wave properties of electrons—their ability to diffract or bend, for example. American physicists Clinton Davisson and Lester Germer and English physicist George Paget Thomson all proved that de Broglie had been correct. Later experiments would demonstrate that de Broglie's theory also explained the behavior of protons, atoms, and even molecules. These properties later found practical applications in the development of magnetic lenses, the basis for the electron microscope.

De Broglie devoted the rest of his career to teaching and to developing his theory of wave mechanics. In 1927, he attended the seventh Solvay Conference, a gathering of the most eminent minds in physics, where wave mechanics was further debated. Theorists such as German physicist Werner Karl Heisenberg, Danish physicist Niels Bohr, and English physicist Max Born favored the uncertainty or probabilistic interpretation, which proposed that the wave associated with a particle of matter provides merely statistical information on the position of that particle and does not describe its exact position. This interpretation was too radical for Schrödinger, Einstein, and de Broglie; the latter postulated the "double solution," claiming that particles of matter are transported and guided by continuous "pilot waves" and that their movement is essentially deterministic. De Broglie could not reconcile his pilot wave theory with some basic objections raised at the conference, however, and he abandoned it.

The disagreement about the manner in which matter behaves described two profoundly different ways of looking at the world. Part of the reason that de Broglie, Einstein, and others did not concur with the probabilistic view was that they could not philosophically accept that matter, and thus the world, behaves in a random way. De Broglie wished to believe in a deterministic atomic physics, where matter behaves according to certain identifiable patterns. Nonetheless, he reluctantly accepted that his pilot wave theory was flawed and throughout his teaching career instructed his students in probabilistic theory, though he never quite abandoned his belief that "God does not play dice," as Einstein had suggested.

In 1928, de Broglie was appointed professor of theoretical physics at the University of Paris's Faculty of Science. De Broglie was a thorough lecturer who addressed all aspects of wave mechanics. Perhaps because he was not inclined to encourage an interactive atmosphere in his lectures, he had no noted record of guiding young research students.

In 1929, at the age of thirty-seven, de Broglie was awarded the Nobel Prize for physics in recognition of his contribution to wave mechanics. In 1933, he accepted the specially created chair of theoretical physics at the Henri Poincaré Institute—a position he would hold for the next twenty-nine years—where he established a center for the study of modern physical theories. That same year, he was elected to the Académie des Sciences, becoming its Life Secretary in 1942; he used his influence to urge the Académie to consider the harmful effects of nuclear explosions as well as to explore the philosophical implications of his and other modern theories.

In 1943, anxious to forge stronger links between industry and science and to put modern physics, especially quantum mechanics, to practical use, de Broglie established a center within the Henri Poincaré Institute dedicated to applied mechanics. He was elected to the prestigious Academie Francaise in 1944 and, in the following year, was appointed a counsellor to the French High Commission of Atomic Energy with his brother Maurice in recognition of their work promoting the peaceful development of nuclear energy and their efforts to bridge the gap between science and industry. Three years later, de Broglie was elected to the National Academy of the United States as a foreign member.

During his long career, de Broglie published over twenty books and numerous research papers. His preoccupation with the practical side of physics is demonstrated in his works dealing with cybernetics, atomic energy, particle accelerators, and wave-guides. His writings also include works on X rays, gamma rays, atomic particles, optics, and a history of the development of contemporary physics. He served as honorary president of the French Association of Science Writers and, in 1952, was awarded first prize for excellence in science writing by the Kalinga Foundation. In 1953, de Broglie was elected to London's Royal Society as a foreign member and, in 1958, to the French Academy of Arts and Sciences in recognition of his formidable output. With the death of his older brother Maurice two years later, de Broglie inherited the joint titles of French duke and German prince. De Broglie died of natural causes on March 19, 1987, at the age of ninety-five, having never fully resolved the controversy surrounding his theories of wave mechanics.

Further Reading on Louis de Broglie

Cline, Barbara Lovett, Men Who Made a New Physics, University of Chicago Press, 1987.

Guillemin, Victor, The Story of Quantum Mechanics, Scribner, 1968.

Heathcote, Niels H., Nobel Prize Winners in Physics, 1901-1950, Books for Libraries Press, 1953.

Modern Men of Science, Volume II, McGraw-Hill, 1968.

Weber, Robert L., Pioneers of Science: Nobel Prize Winners in Physics, Institute of Physics, 1980.

Proceedings of the Royal Society, Volume 34, 1988.