Louis de Broglie

Louis-Victor Pierre Raymond de Broglie [lwiː vikˈtɔʀ pjɛːʀ ʀɛˈmɔ̃ də ˈbʀœj] listen^{? /i} (* 15 August 1892 in Dieppe, Normandy; † 19 March 1987 in Louveciennes, Département Yvelines) was a French physicist. He belonged to the noble French family of the Broglies and was younger brother of the experimental physicist Maurice de Broglie.

De Broglie is considered one of the most important physicists of the 20th century, for his discovery of the wave nature of the electron (wave-particle duality) in his dissertation Recherches sur la théorie des quanta and the resulting theory of matter waves he received the Nobel Prize in Physics in 1929.

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Studies and the First World War

Louis-Victor de Broglie, fourth child of Victor de Broglie, 5th Duke de Broglie and Pauline d'Armaillé, was born in Dieppe in 1892. Louis-Victor attended the Lycée Janson de Sailly in Paris. In 1960, he succeeded his childless brother Maurice as Duke.

During his studies at the Sorbonne in Paris, Louis-Victor first studied philosophy and history, especially the history of law and the political history of the Middle Ages. Along the way he read works by Henri Poincaré such as Science and Hypothesis and The Value of Science. In 1910 he completed his first degree with the licentiate.

At the suggestion of his seventeen year older brother Maurice, a physicist with a doctorate, Louis de Broglie studied mathematics and physics from 1911. Maurice, who had taken care of the education and development of his younger brother after his father's death in 1906, now provided Louis with the texts of the papers and discussions of the first Solvay Conference, which took place in Brussels in 1911. It was through these notes that Louis de Broglie first came into intensive contact with quantum physics, which was to shape his later work in physics.

The First World War forced de Broglie to interrupt his studies for several years. He became an intelligence officer and spent most of his service time in the radio-telegraphic station of the Eiffel Tower. During his military service, de Broglie was involved in electrical engineering and communications, as well as the training of electrical engineering personnel.

Scientific career

After his discharge from the army in 1919, de Broglie continued his studies and became a collaborator in his brother's private laboratory, where he worked primarily on X-ray spectroscopy and the photoelectric effect. At the end of 1923, de Broglie's first papers on wave mechanics appeared.

In 1924, de Broglie graduated with the famous dissertation Recherches sur la théorie des Quanta, in which he suggested that wave-particle duality could be applied to any solid matter. This bold idea was honored by the Institut de France in 1926 and again in 1927. In 1929, the discovery of the wave nature of electrons was followed by the coveted Henri Poincaré Medal of the Académie des sciences and the Nobel Prize in Physics.

De Broglie was one of the participants in the famous 5th Solvay Conference in Brussels in 1927 and also attended the 7th and last conference before the war in 1933. In 1929 he was appointed professor of theoretical physics at the Institut Henri Poincaré in Paris, but in 1932 he moved to the Sorbonne, where he taught until 1962. In 1933 de Broglie became a member of the Académie des sciences.

In addition to his work in the field of physics, de Broglie published several philosophical and problem-historical essays, especially during his time at the Institut Henri Poincaré. In 1938 he received the Max Planck Medal of the German Physical Society.

World War II and after

During the fighting between France and Germany in World War II, de Broglie was entrusted with the documentary collection of work published in the USA on communications transmission. In 1941, he published a book on high frequency technology in this context.

De Broglie's patriotism during the German occupation is expressed in his memorial lecture for the French scholar André-Marie Ampère in September 1940:

In 1944 Louis de Broglie became a member of the Académie française and after the Second World War he became an adviser to the French Atomic Energy Commission.

De Broglie submitted the first official proposal for a European nuclear research laboratory for discussion at the European Cultural Conference in Lausanne in December 1949. A proposal that led to the creation of the European Organization for Nuclear Research (CERN).

Louis-Victor de Broglie died on 19 March 1987 in Louveciennes near Paris.

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Early research

In his early research, especially while working in the physics laboratory of his brother Maurice, de Broglie was concerned with the photoelectric effect of X-rays. In 1928 he published a book on X-ray physics with his brother. In the early 1920s he devoted himself to quantum theory. He succeeded in deriving Max Planck's quantum formula from the particle theory of light.

A bold doctoral thesis - electrons with wave properties

In 1924, de Broglie completed his studies with the famous dissertation Recherches sur la théorie des quanta (Investigations into quantum theory). After a thorough analysis of the equivalence of mass and energy found by Albert Einstein, which is expressed in the formula , and the findings of atomic physics, de Broglie comes to the conviction that energy, like mass, is localized in the form of particles in small areas of space. However, the quantum character of matter, as it appears for example in the atomic spectra, can only be explained if a frequencyassigned to each mass according to the relation ν postulated by Max Planck. According to de Broglie, this frequency characterizing the particle is not limited to the particle volume, but is also present in a large spatial domain in the form of a wave accompanying the particle. De Broglie calls this accompanying wave a phase wave, because particle and wave are coupled to each other via the phase at the location of the particle. Under this condition, both particle and wave satisfy the transformation laws of special relativity.

The wave-particle-dualism, which at that time was known only for photons, is according to de Broglie an essential feature not only of photons but also of matter. Thus, even a classical particle - e.g. an electron - can be said to have wave properties. In the rest system of the particle, the wavelength of the phase wave is infinite. If the particle is in motion, the application of the Lorentz transformation results in a modulation of the wave with the so-called De Broglie wavelength

i.e. the wavelength λ of the particle is equal to the quotient of the Planck action quantum by the momentum of the particle.

The examination board of the Paris Sorbonne, which included the well-known physicists Jean-Baptiste Perrin and Paul Langevin, was unsure how to react to this bold and experimentally unconfirmed proposal. De Broglie himself, referring to Paul Langevin's scepticism, said that the latter was " probablement un peu étonné par la nouveauté de mes idées " (probably a little taken aback by the novelty of my ideas).

Langevin asked de Broglie for a second copy of his work and sent it to Albert Einstein, who in turn informed Max Born. Einstein was deeply impressed and later declared that he believed de Broglie's thesis threw the first faint ray of light on this most vexing of physical puzzles. Max Planck later reported how unusual he initially found de Broglie's new thoughts:

The examination board finally accepted de Broglie's thesis. The experiments of Clinton Davisson and Lester Germer in 1927 (Davisson-Germer experiment) and of George Paget Thomson in 1928 confirmed the wave character of electrons also experimentally.

Matter waves

Based on his realization that all particles also possess wave properties, de Broglie worked on improving Bohr-Sommerfeld's atomic model after his doctorate. He assigned a so-called matter wave to each particle of matter, which propagates along Bohr's orbits. In this way, De Broglie showed the relationship between the orbital stability and the orbital circumference of the electrons in the Bohr atomic model:

,

i.e. an electron can only move around the atomic nucleus without losing energy if its orbital circumference is an integer multiple of its wavelength. In 1926, de Broglie set about formulating a differential equation that described the behavior of electrons. These approaches provided important ideas for Erwin Schrödinger, who in the same year formulated his partial differential equation (Schrödinger equation). This was able to represent the behavior of electrons in the stationary energy states.

In further work de Broglie devoted himself to the quantum field theory of elementary particles and wave equations for particles with higher spin.

Philosophical approach

At first, Louis de Broglie tried to explain the wave mechanics of particles deterministically, and thus to represent all processes in an exactly calculable way. After the fifth Solvay Congress in 1927, where he had lively discussions with other famous physicists of the time such as Albert Einstein, Niels Bohr, Max Planck and others, he abandoned the deterministic approach and approached the probability interpretation. It was not until 1951 that de Broglie again approached a causal and concrete interpretation of wave mechanics through the work of David Bohm and Jean-Pierre Vigier. →De Broglie-Bohm theory

Through de Broglie's philosophical and problem-historical essays, which date mainly from his time at the Institut Henri Poincaré in Paris, it becomes clear that de Broglie's preoccupation with fundamental physical problems was often based on his historical interest. For example, his idea of matter waves ultimately emerged from his intensive study of the history of the theory of light.