This article is from the magazine Les Indispensables de Sciences et Avenir n°212 dated January/March 2023.
The photo is historic. In October 1927, in Brussels, twenty-nine scientists posed for posterity. Their list is dizzying: Einstein, Langevin, Planck, Bohr, Dirac, Heisenberg… and only one woman: Marie Curie. All of them have published physics works of capital importance, which have benefited from the extraordinary emulation of the “Solvay councils” organized since 1911… And no less than seventeen will receive the Nobel Prize.
Belgian industrialist Ernest Solvay made his fortune in chemicals. “Self-taught, he is passionate about science, to the point of constructing his own theories, says Franklin Lambert, Emeritus Professor of Mathematical Physics at the Free University of Brussels. However, aware of its lack of fundamental knowledge, he sends memoirs to the Academy of Sciences anonymously, under seal. He even asks for his aid to Marie Curie. Above all, he wishes to support the work of professional physicists.” For this, it will generously grant credits, financing the work of researchers, six of whom will receive a Nobel Prize. But by chance, he will go further.
It all started when, in 1911, he was approached by the German physicist and chemist Walther Nernst who, disturbed by some of his experimental results, wanted to compare his work with that of his peers, in particular Einstein, who worked on his object of study. . “Unlike chemists, physicists were then poorly organized at the international level, emphasizes Franklin Lambert. A meeting had been organized in Paris in 1900, at the time of the Universal Exhibition, but it remained without follow-up.
This article is from the magazine Les Indispensables de Sciences et Avenir n°212 dated January/March 2023.
The photo is historic. In October 1927, in Brussels, twenty-nine scientists posed for posterity. Their list is dizzying: Einstein, Langevin, Planck, Bohr, Dirac, Heisenberg… and only one woman: Marie Curie. All of them have published physics works of capital importance, which have benefited from the extraordinary emulation of the “Solvay councils” organized since 1911… And no less than seventeen will receive the Nobel Prize.
Belgian industrialist Ernest Solvay made his fortune in chemicals. “Self-taught, he is passionate about science, to the point of constructing his own theories, says Franklin Lambert, Emeritus Professor of Mathematical Physics at the Free University of Brussels. However, aware of its lack of fundamental knowledge, he sends memoirs to the Academy of Sciences anonymously, under seal. He even asks for his aid to Marie Curie. Above all, he wishes to support the work of professional physicists.” For this, it will generously grant credits, financing the work of researchers, six of whom will receive a Nobel Prize. But by chance, he will go further.
It all started when, in 1911, he was approached by the German physicist and chemist Walther Nernst who, disturbed by some of his experimental results, wanted to compare his work with that of his peers, in particular Einstein, who worked on his object of study. . “Unlike chemists, physicists were then poorly organized at the international level, emphasizes Franklin Lambert. A meeting had been organized in Paris in 1900, at the time of the Universal Exhibition, but it remained without follow-up.
The quantum revolution begins
Solvay agrees to Nernst’s request: it creates a “council” of around twenty scientists, chaired by the Dutch physicist Hendrik Lorentz. This private meeting, accessible only by invitation, brings together a small number of leading scientists. It is organized with a lot of diplomacy because the tensions between France and Germany are already palpable. Solvay invites French and British in large numbers and chooses Brussels, neutral ground. Polyglot, Lorentz will take care of the translation and will summarize the interventions of each, while the French Maurice de Broglie will transcribe the debates.
As will become the rule, the advice relates to a precise theme, in this case the kinetic theory, which explains the temperature and the pressure of a gas by the movement of the particles which compose it. “The physics is then in crisis, continues the Belgian historian. The quantum hypothesis does it call into question this kinetic theory, and more generally all of physics, or can it be integrated into the general framework? At the end of this first council, the question is not settled. But back in Paris, one of the participants, the physicist and mathematician Henri Poincaré, published a article demonstrating that the quantum hypothesis is unavoidable.” The quantum revolution has just begun…
The second council, in 1913, will also give rise to a high-level confrontation: the New Zealander Ernest Rutherford (1871-1937) exhibits there his innovative model of the atom, consisting, according to him, of a nucleus containing the positive charges around which the negatively charged electrons revolve. This, against the advice of Joseph John Thomson (1856-1940), discoverer of the electron and… his former teacher! The latter sees the atom as a “pudding”, a paste of positive matter in which electrons move…
The scene of famous controversies, the councils are also an opportunity to forge links and set up networks. A community of physicists is forming. It will survive the First World War, even if the Germans will not be back in Brussels until 1927. This edition focuses on the theme “electrons and photons”. “It was very fertile. Because it was notably thanks to the stimulating objections of Einstein that the German physicist Werner Heisenberg was able to establish his relation of uncertainty”, emphasizes Franklin Lambert. This stipulates that at the microscopic scale, it is not possible to accurately measure both the position and the speed of a particle.
The brilliant Solvay Congress of 1927. From left to right, third row: Auguste Piccard, Émile Henriot, Paul Ehrenfest, Édouard Herzen, Théophile de Donder, Erwin Schrödinger, Jules-Émile Verschaffelt, Wolfgang Pauli, Werner Heisenberg, Ralph H. Fowler , Leon Brillouin. Second row: Peter Debye, Martin Knudsen, William Lawrence Bragg, Hendrik Anthony Kramers, Paul Dirac, Arthur Compton, Louis de Broglie, Max Born, Niels Bohr. Front row: Irving Langmuir, Max Planck, Marie Curie, Hendrik Lorentz, Albert Einstein, Paul Langevin, Charles-Eugène Guye, Charles Thomson Rees Wilson, Owen Willans Richardson. Credit: DARCHIVIO/OPALE.PHOTO
“Of the very heated discussions
The 1927 council will also be the scene of a daunting confrontation, destined to last for years, between Albert Einstein and the Danish physicist Niels Bohr. At the heart of the discord: this famous principle of uncertainty which gives a “statistical” character to quantum objects. Einstein does not question the quantum theory, but thinks that there are laws allowing to describe all the properties of each object. Bohr argues that such laws are unnecessary. “The testimonies of Heisenberg, Ehrenfest and Bohr, published in the 1960s, make account of very heated discussions, says Franklin Lambert. Many took place informally, at the hotel, the morning or evening! History will prove Einstein wrong. …”
The 1927 congress saw Niels Bohr and Albert Einstein clash theatrically over a crucial question: could we be able to define both the position and the speed of a particle? The discussions between the two men will continue for years, often informally. Credit: SPL/SUCRÉ SALÉ
After the atom, physicists are tackling the study of its nucleus. In 1932, the Briton James Chadwick discovered one of its components, the neutron. The council of 1933 relates in particular to the nature of this one. Its neutral character means that it can be used as a projectile on other atoms, of which it bursts the nuclei with a significant emission of energy. This is fission, which will soon be implemented in all nuclear reactors. That same year, three women who had played a major role in nuclear physics were present in Brussels: Marie Curie, her daughter Irène Joliot-Curie (who would discover artificial radioactivity with her husband Frédéric), and the Austrian Lise Meitner (1878- 1968), forgotten by the Nobel Prize despite the importance of her work – she will discover fission with the German chemist Otto Hahn, without being associated with this discovery because in 1938, a Jewish researcher could not publish her work in a German journal.
In fact, from 1933, with the rise of Nazism in Germany, the clouds were gathering over Europe and the Solvay councils. The Frenchman Paul Langevin, who took over from Lorentz, could not join that of 1936 for health reasons. Three years later, a council devoted to nuclear physics, to which American physicists were invited, will not take place either. The war breaks out, the Americans get involved in the Manhattan project, while their German colleagues – Heisenberg at their head – put themselves at the service of the Third Reich. We know the rest. From 1948, the councils resume, but the golden age has passed. “The center of gravity of physics research has shifted to the United States”emphasizes Franklin Lambert.
Since then, the councils, crowned with their prestige, have never ceased. Still in a select committee, they take place according to a three-year plan: physics the first year, chemistry the third, with a blank year in between. “Inasmuch as young guest researcher, in 1991, I had the opportunity to meet the big names in the field”remembers the physicist Jean Dalibard. “Solvay advice does not probably play more a role as important as beginning of the 20th century, but they bring a different perspective, and often with more hindsight on a given area”emphasizes Antoine Browaeys, researcher at the Institute of Optics at the University of Paris-Saclay.
The choice of theme reflects the spirit of the times: the 2022 edition was devoted to “the physics of quantum information”. “It’s a new way of looking at problems such as condensed matter, the physics of high energies and cosmology. The discussions also focused of course black holes than quantum computers”, specifies the physicist. A few months later, the Nobel Prize was awarded to three physicists at the cutting edge of quantum information: the American John Clauser, the Austrian Anton Zeilinger… and the Frenchman Alain Aspect.
