This November 25 marks the centenary of the presentation of Louis de Broglie’s doctoral thesis, which earned him a Nobel Prize for “his discovery of the wave nature of electrons”. This work has had a lasting impact on physics and constitutes one of the pioneering contributions to quantum physics.
An important development of this work led to the so-called “pilot wave” model, which constitutes an alternative to the standard formulation of quantum mechanics, and whose influence still persists today… but which Louis de Broglie quickly disowned . For what reasons?
Difficulties in interpreting quantum mechanics
The theory of quantum mechanics describes the behavior of matter at small scales, for example that of atoms or electrons. Its discovery dates from the beginning of the 20th century.e century, but many questions remain debated even today. This situation is due, in large part, to the confusing features of the theory.
For example, quantum objects seem to behave sometimes like particles, sometimes like waves. The Copenhagen interpretation, developed at the beginning of the 20the century, concludes that the quantum world cannot be analyzed according to classical concepts. This reading of quantum mechanics encountered significant objections, and a causal and mechanical representation of the quantum world remained sought by a whole section of the research community (including by Albert Einstein).
Louis de Broglie, a French physicist, shared this ambition, and proposed his “pilot wave theory” in 1927. According to this model, matter is composed of particles, whose movement is guided by a “quantum wave”. This theory would thus explain the reasons for the wave behavior of particles.
However, a few years after this discovery, he gave up his theory. Why this change of heart by Louis de Broglie himself, and what was the impact of his work on the rest of the scientific community?
The strangeness persists
The causes of the renunciation of the pilot wave theory are multiple. However, two features of the model made it particularly suspect. On the one hand, it suggests that the movement of a particle can depend on that of another, even if their distance, according to Einstein’s relativity, should prohibit any interaction.
On the other hand, the pilot wave does not have a clear physical meaning. Unlike conventional waves, such as ocean waves or electromagnetic waves, it is not a wave that evolves in our three-dimensional physical space. Rather, it is a wave that unfolds in an abstract mathematical space with a large number of dimensions, making its interpretation difficult.
These aspects of his pilot wave were very disturbing to Louis de Broglie, who explicitly abandoned his theory in his later writings. His deeper ambition was to develop a somewhat different approach, called “double solution theory”.
This alternative model would have had the advantage of being much more intuitive and easier to understand. Its main object would have been a less abstract wave, which would unfold within the space familiar to our perception.
However, the mathematical complexity of this approach was considerable. Louis de Broglie worked on it until the end of his life, despite the project’s poor reception among his fellow physicists. Indeed, despite its defects highlighted by de Broglie, it is the pilot wave theory which has attracted the attention of the vast majority of researchers, leading to the gradual forgetting of its research program on the double theory. solution.
Rediscovery of theory
Despite everything, Louis de Broglie’s work profoundly influenced the scientific community.
Thus, the American physicist David Bohm, who made important contributions to quantum physics, independently rediscovered the pilot wave theory in 1952. Rather than rejecting the model because of its strangeness, the challenge was his give meaning. Questions regarding the content and exact meaning of the theory are still debated today.
On the other hand, Louis de Broglie’s theory of the double solution was not completely abandoned. Some contemporary physicists are still working on its formulation. It may be that this approach could one day help us better understand our world on a small scale, with reduced impact on our classical intuitions.
This article benefited from discussions with Aurélien Drezet, from the Néel Institute in Grenoble, whom the author would like to thank.
