Majorana equation, Majorana forces, Majorana transformation, Majorana algebra, Majorana neutrino, Majorana fermions, Majorana sphere… Fundamental physics seems to be in an advanced “majoranization” phase. But who was the one whose name is today associated with so many concepts?
Born in 1906 in Catania, Sicily, Ettore Majorana was a pure theoretician, a dazzling researcher, a productive physicist until he vanished one evening in March 1938, exactly eighty-six years ago. From the 1960s, some of his ideas, which had long remained in the shadows, even in the cemetery of oblivion, ended up becoming alive: they first took a new look at the properties of the neutrino, this elementary particle discovered in 1956; then they opened new avenues regarding certain fundamental problems, such as that of hypothetical dark matter, this invisible matter, of still unknown nature, which seems much more abundant in the universe than ordinary matter; and more recently, they have infused even the field of quantum computers, where they also suggest small revolutions.
However, Ettore Majorana’s career only lasted barely ten years. It began in earnest in 1928, when Enrico Fermi welcomed this thin young man, with dark, incandescent eyes, into his laboratory in Rome. The Italian mentor very quickly realized that he was facing an authentic genius, of the same caliber as Galileo and Newton: “Majorana has gifts that he is the only one to possess in our time”, he wrote. But in addition to this portrait, Fermi added that Majorana lacked what is common to find in other men: simple “common sense”, that is to say a kind of ordinary pragmatism without which Daily life can easily turn into a disaster. Majorana indeed struggled to live serenely among his peers, and it was the pessimistic and tormented inclination of his soul which, undoubtedly, ended up determining his choice to disappear for good, or to go elsewhere. He announced it through an enigmatic letter that he sent on March 25, 1938 to the director of the Institute of Physics in Naples, where he taught.
Majorana, the equivalent of a quantum particle
“I have made a decision which is now inevitable,” he wrote. “There is not a drop of selfishness in it, but I realize that my impromptu disappearance risks being a source of trouble for you as for the students. This is why I ask you to forgive me, especially for having disappointed your trust and the sympathy you showed towards me. I ask you to remind me of the good memories of those I learned to know and appreciate in your Institute. Of all of them, I will keep a happy memory at least until eleven o’clock this evening, and, if possible, even after.”
The same evening he boarded a mail ship traveling from Naples to Palermo, then disappeared. Many hypotheses were put forward, but no one knows what really happened to him. Majorana therefore appears retrospectively as the equivalent of a quantum particle whose destiny superimposes a multitude of possible trajectories, without any of them being considered more real than the others.
A certain idea of modernity equates it with the rapid promotion of innovation. Each of Majorana’s articles, on the contrary, seems to tell us, like a Sleeping Beauty: “I’m waiting quietly, you see, friends, because I have plenty of time.” His most prophetic article was published in 1938. It concerns antiparticles, which he describes by inventing a very original mathematical formalism. According to his equations, neutral particles, that is to say those which are devoid of electrical charge, are necessarily identical to their own antiparticles (more precisely, electrically neutral particles must have as antiparticles their own image in a mirror ). Such particles, called “Majorana” particles, are still only hypothetical, but intense research is now being carried out to try to detect them, because their properties suggest that they could well be constituents of dark matter.
Ettore Majorana was an evanescent being, but his work may soon make the news. Like thunder, some physicists only make their rumble heard a long time later.
Etienne Klein is a physicist, research director at the CEA and philosopher of science
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