# Louis de Broglie

Louis-Victor de Broglie (1929)

Louis-Victor Pierre Raymond de Broglie [ LWI viktɔʀ pjɛːʀ ʀɛmɔ də bʀœj ] listen ? / i (born  August 15, 1892 in Dieppe , Normandy ; † March 19, 1987 in Louveciennes , Yvelines department ) was a French physicist . He belonged to the French aristocratic family of the Broglies and was the 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 dualism ) 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 .

## Life

### Studies and World War I

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 initially dealt with philosophy and history , in particular with legal history and the political history of the Middle Ages . He also read works by Henri Poincaré such as B. Science and Hypothesis and The Value of Science . In 1910 he completed his first degree with a licentiate .

At the suggestion of his brother Maurice , who was seventeen years older than him and a doctor of physics, Louis de Broglie studied mathematics and physics from 1911 . Maurice, who had taken care of the upbringing and development of his younger brother after his father's death in 1906, now provided Louis with the texts for the presentations and discussions at the first Solvay conference , which took place in Brussels in 1911 . Through these notes, Louis de Broglie came into close contact with quantum physics for the first time , which was to shape his later physical work.

Due to the First World War , de Broglie had to interrupt his studies for several years. He became an intelligence officer and spent most of his service time in the Eiffel Tower's radiotelegraphic station . During his military service, de Broglie dealt with electrical engineering and communications, as well as with the training of electrical engineering personnel.

### Scientific career

After his discharge from army service in 1919, de Broglie continued his studies and worked in his brother's private laboratory, where he mainly worked on X-ray spectroscopy and the photo effect . De Broglie's first treatises on wave mechanics appeared at the end of 1923.

In 1924 de Broglie completed his studies with the famous dissertation Recherches sur la théorie des Quanta , in which he assumed that the wave-particle dualism could be applied to all solid matter. This bold idea was recognized by the Institut de France in 1926 and 1927 . In 1929, the coveted Henri Poincaré medal from the Académie des Sciences and the Nobel Prize in Physics followed for the discovery of the wave nature of electrons .

De Broglie was one of the participants in the famous 5th Solvay Conference in Brussels in 1927 and also participated in 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 physical field, de Broglie published some 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 the works published in the USA on telecommunications . 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 commemorative lecture for the French scholar André-Marie Ampère in September 1940:

And that is precisely why a great man like Ampère is a shining example for posterity. - In the current times when everything calls the French to collect, it is salutary for them to ponder such examples. When we turn our minds to them, we suddenly see all the great figures of France's glorious past appear before us, as if calling us to hope for a new spring and to work. "

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

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

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

## Services

### Early research

In his early research, especially while working in his brother Maurice's physical laboratory, de Broglie dealt with the photoelectric effect of X-rays . In 1928 he and his brother published a book on X-ray physics. In the early 20s 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. The quantum character of matter, as it is shown, for example, in the atomic spectra, can only be explained if a frequency is assigned to each mass according to the relationship postulated by Max Planck . According to de Broglie, this frequency, which characterizes the particle, is not limited to the particle volume, but is also present in a large area in the form of a wave accompanying the particle. De Broglie calls this accompanying wave phase wave, because the particle and wave are coupled to each other via the phase at the location of the particle. Under this condition, both the particle and the wave fulfill the transformation laws of the special theory of relativity . ${\ displaystyle E = mc ^ {2}}$${\ displaystyle m}$ ${\ displaystyle E = h \ nu}$${\ displaystyle \ nu = mc ^ {2} / h}$

The wave-particle dualism , which at that time was only known for photons , is, according to de Broglie, a characteristic not only of photons, but also of matter. Even a classic particle - e.g. B. an electron - can thus be attributed wave properties. In the rest system of the particle the wavelength of the phase wave is infinitely large. 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

${\ displaystyle \ lambda = {h \ over p} \,}$

d. H. the wavelength of the particle is equal to the quotient of Planck's constant of action by the momentum of the particle. ${\ displaystyle \ lambda}$ ${\ displaystyle h}$ ${\ displaystyle p = mv}$

The examination board of the Paris Sorbonne, which also included the well-known physicists Jean-Baptiste Perrin and Paul Langevin , was unsure how to respond to this bold and experimentally unconfirmed proposal. De Broglie himself said of Paul Langevin's skepticism that he was “  probablement un peu étonné par la nouveauté de mes idées  ” ( probably a little astonished at 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 that de Broglie's doctoral thesis cast the first faint ray of light on this most tiresome of the physical riddles. Max Planck later reported how unusual he initially felt de Broglie's new thoughts:

The boldness of this idea was so great - I have to honestly say that I shook my head about it myself back then , and I remember very well that Mr. Lorentz said to me in a confidential private conversation at the time: 'These young people are really gaining weight easy to put old physical terms aside! ‛At that time there was talk of Broglie waves, of Heisenberg's uncertainty relation - that seemed to us older people to be very difficult to understand. "

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

### Matter waves

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

${\ displaystyle 2 \ pi r = n \ lambda \ Leftrightarrow 2 \ pi r = {nh \ over p}}$,

d. H. an electron can only move around the atomic nucleus without loss of energy if its orbit circumference is an integral multiple of its wavelength. In 1926 de Broglie set out to formulate a differential equation that described the behavior of electrons. These approaches provided important suggestions for Erwin Schrödinger , who in the same year set up his partial differential equation ( Schrödinger equation ). This could represent the behavior of the 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

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

Through de Broglie's philosophical and problem-historical essays, which stem 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. So went z. B. his idea of ​​matter waves ultimately emerged from the intensive study of the history of light theory .

## literature

• Wolfgang Schreier (Ed.): Biographies of important physicists. A collection of biographies . Verlag Volk und Wissen, Berlin 1988, ISBN 3-06-022505-2
• Henning Sievers: Louis de Broglie and quantum mechanics . July 3, 1998, arxiv : physics / 9807012v2 (very detailed German biography, which also illuminates the relationship to Einstein).
• Emilio Segrè: The great physicists and their discoveries . Special edition, 2nd edition. Piper, Munich / Zurich 1997, ISBN 3-492-03950-2 .