“Towards the end of January, 1932, we began to receive the issues of the “Comptes rendues” containing the famous notes by F. Joliot and I. Curie on the penetrating radiation discovered by Bothe and Becker. In the first of these notes it was shown that the penetrating radiation emitted by Be under bombardment with polonium alfa particles could transfer kinetic energies of about 5 millions electron volts to the proton present in small layers of various hydrogenated materials (such as water or cellophane). In order to interpret these observations the Joliot-Curies (1923) at first put forward the hypothesis that the phenomenon was similar to the Compton effect, namely that the incident photon undergoes an elastic collision with a proton; they had calculated, by applying the laws of energy and momentum conservation, that the incident photons should have had an energy of about 50 million electron volts in order to be able to transfer such high energy to a proton. However, they had very soon realized that when Klein and Nishina’s formula was applied to the protons, the cross-section was too small by many orders of magnitude, and had suggested that the effect observed was due to a new type of interaction between gamma rays and protons, different from that responsible for the Compton effect. When Ettore read these notes he said, shaking his head:

“They haven’t understood a thing. They are probably recoil protons produced by a heavy neutral particle”.

A few days later we got, in Rome, the issue of Nature containing the letter to the editor from Chadwick dated 17 February, 1932, entitled “Possible existence of a neutron”, in which he demonstrated the existence of the neutron on the basis of a classical series of experiments, in which recoil nuclei of some light elements (such as nitrogen, for instance), were observed in addition to recoil protons. Amaldi continues: “Soon after Chadwick’s discovery, various authors understood that the neutron must be one of the components of the nucleus and began to propose various models which included alfa particles, protons, electrons and neutrons.

The first to publish the idea that the nucleus consists solely of protons and neutrons was probably Iwanenko (1932). Neither I nor his other friends questioned remember whether Ettore Majorana came to this conclusion independently. What is certain is that before Easter (18 Apr) of that year (1932):

“[Majorana] worked out a theory on light nuclei, assuming that they consisted solely of protons and neutrons (or neutral protons as he then said) and that the former interacted with the latter through exchange forces. He also reached the conclusion that these exchange forces must act only on the space co-ordinates (and not on the spin) if one wanted the alfa particle, and not the deuteron, to be the system saturated with respect to binding energy”.

He talked about this outline of a theory to his friends at the Institute, and Fermi, who had at once realized its interest, advised him to publish his results as soon as possible, even though they were partial. However, Ettore would not hear of this, because he considered his work to be incomplete. Thereupon, Fermi, who had been invited to participate in the Physics conference which was to take place in July of that year in Paris in the wider framework of the Fifth International Conference on Electricity, and who had chosen as his subject the properties of the atomic nucleus, asked Majorana for permission to mention his ideas on nuclear forces. Majorana forbade Fermi to mention them but added that if he really must he should say they were the ideas of a well-known professor of electrical engineering who, among others, was to be present at the Paris conference and whom Majorana considered to be a living example of how not to carry out scientific research.

Thus, on 7 July, Fermi presented his report in Paris on “The Present State of the Physics of the Atomic Nucleus” (1932) without mentioning the type of force which was subsequently called “Majorana force” and which had actually been thought of, although in a crude form, some months earlier. The issue of the “Zeitschirft für Physick” dated 19 July, 1932, contained Heisenberg’s first paper on “Heisenberg’s exchange forces”, namely forces involving the exchange of both the space and spin coordinates.

This paper made a great impression in the scientific world; it was the first attempt to put forward a theory of the nucleus which, although incomplete and imperfect, succeeded in overcoming some theoretical difficulties which had so far seemed insurmountable. Everyone at the Physics Institute of the University of Rome was extremely interested and full of admiration for Heisenberg’s results, but at the same time disappointed that Majorana had neither published nor even allowed Fermi to mention his ideas at an international conference. Heisenberg’s paper tackled the problem from a wider and fuller point of view but Ettore Majorana had completely understood, or so at least it appeared to us, the consequences of the action of the exchange forces in so far as the binding energy of light nuclei was concerned.

Fermi again tried to persuade Majorana to publish something, but all his efforts and those of his friends and colleagues were in vain. Ettore replied that Heisenberg had now said all there was to be said and that, in fact, ha had probably even said too much. Finally, however, Fermi succeeded in persuading him to go abroad, first to Leipzig and then to Copenhagen, and obtained a grant from the National Research Council for his journey, which began at the end of January, 1933 and lasted six or seven months.”

“When he returned to Rome in the autumn of 1933, Ettore was not in good health, because of gastritis which he had developed in Germany. It is not clear what caused this, but the family doctors attributed it to nervous exhaustion.

He began to attend the Institute in the Via Panisperna only at intervals, and after some months no longer came at all: he tended more and more to spend his days at home immerse in study for a quite extraordinary number of hours.

At that time he was more interested in political economy, politics, the fleets of various countries and their respective power, and the constructional characteristics of the ships than in physics. At the same time his interest in philosophy, which had always been great, increased and prompted him to reflect deeply on the works of various philosophers, particularly Schopenhauer. It was probably at this time that he wrote the paper on “The Value of Statistical Laws in Physics and Social Sciences”, which was found among his papers by his brother Luciano, and was published after his disappearance by Giovanni Gentile junior.

A considerable number of attempts by Giovanni Gentile junior, Emilio Segré and myself to bring him back to living a normal life met with no success. I remember that in 1936 he rarely left the house, not even to go to the barber’s, and his hair was therefore abnormally long; during this period some of his friends who had been to see him sent him a barber, in spite of his protests. However, non of us succeeded in finding out whether he was still doing theoretical physics research; I believe he was, but I have no proof.”

“Ettore was too intelligent. If he has decided to disappear, no one will be able to find him. Nevertheless, we have to consider all possibilities.”

"Half-way through 1937 public examinations held for various professorships, Majorana enters the field, said to have been motivated by Fermi’s international recognition; likewise his friends at the Institute of Physics put "pressure" [social pressure] [peer pressure] on him to apply, but Majorana had doubts. However, they do persuade him to publish an article he has kept in a drawer for five years. He wrote this article in 1932 and in it he qualifies some aspects of Paul Dirac’s well-known thesis on anti-particles, which continues to be (even today) a work of reference. In the end, without consulting or saying anything to anyone, he makes his decision and applies for the professorship in Palermo. This forced the intervention of senator Gentile, however, alarmed by the formidable competition which Majorana represented for his son, Giovanni Gentile junior. In order to avoid such competition, senator Gentile gets Mussolini to appoint Majorana Professor of Theoretical Physics at the University of Naples in November 1937, supposedly, for his outstanding reputation, without even passing an exam?

Majorana takes up his [diverted] professorship on the 13th January, 1938, and carries out his duties punctually, leading a complete normal life, at least in appearance. But on the 25th March of this same year he sends, from Palermo, a letter to Antonio Carrelli, the director of the Naples Institute of Physics, where he works, in which he says “I have taken a decision which after everything is inevitable”, and that he will give up his classes, and that he will keep fond memories of the professors and students of the Institute “at least until eleven o’clock tonight, and possibly even later”… And the next day, 26th March, Majorana sends a telegram, asking him to ignore the letter, and yet another letter (was it sent at the same time as the telegram?) in which he tells Carrelli that “the sea has rejected me”, but that he does not wish to return to the classes."

“There are several categories of scientists in the world; those of second or third rank do their best but never get very far. Then there is the first rank, those who make important discoveries, fundamental to scientific progress. But then there are the geniuses, like Galilei and Newton. Majorana was one of these.”

“I have no hesitation to state to you, and I am not saying this as an hyperbolic statement, that of all Italian and foreign scholars that I have met, Majorana is among all of them the one that has most struck me for his deep sharpness.”

“Feenberg remembers attending one of Heisenberg’s seminars on nuclear forces, in which Heisenberg also mentioned the contribution made by Majorana to this subject; he said that he author was present and invited him to say something about his ideas, but Ettore refused. When he left the seminar, Uhlenbeck told Feenberg how much he admired Majorana’s penetrating ideas which had been mentioned by Heisenberg.”

● p1. Majorana, Ettore. (1928). “Sullo Sdoppiamento dei Termini Roentgen Ottici a Causa dell’eletrone Rotante e Sulla Intensita delle Righe de Cesio” (“Doubling of Terms on the Roentgen Optics Cause of electrons and rotating on the Intensity of the Lines of Cesium”), Rendiconti Accademica Lincei, 8: 229-33; (in collaboration with Giovanni Gentile Jr).
● p2. Majorana, Ettore. (1931). “Sulla Formazione dello ione Molecolare di He” (“On the Formation of the Molecular Ion of He”), Nuovo Cimento, 8: 22-28.
● p3. Majorana, Ettore. (1931). “I Presunti Termini Anomali dell’Elio” (“The Alleged Anomalous helium Terms”), Nuovo Cimento, 8: 78-83.
● p4. Majorana, Ettore. (1931). “Reazione Pseudopolare fra Atomi di Idrogeno” (“Pseudopolar reaction between hydrogen atoms”), Rendiconti Accademia Linceri, 13: 58-61.
● p5. Majorana, Ettore. (1931). “Teoria dei Triplitti P’ Incomplelti” (“Theory of the Triplet P’ Incomplete”), Nuovo Cimento, 8: 107-12.
● p6. Majorana, Ettore. (1932). “Atomi Orientati in Campo magnetic Variable” (“Oriented Atoms in Variable Magnetic Field”), Nuovo Cimento, 9: 43-50.
● p7. Majorana, Ettore. (1932). “Theoria relativistica di Particelle con Momento Intrinseco Arbitrario” (“Theory of Relativistic Particles with Arbitrary Intrinsic Moment”), Nuovo Cimento, 9: 335-44.
● p8. Majorana, Ettore. (1933). “Uber die Kerntheorie” (“On Nuclear Theory”), Zeitschrift fur Physik, 82: 137-45; “Sulla Theoria dei Nuclei” (“On the Theory of the Nucei”), La ricerca Scientifica, 4(1): 559-65.
● p9. Majorana, Ettore. (1937). “Teoria Simmetrica Dell’elettrone e del Positrone” (“Symmetric Theory of the Electron and Positron”), Nuovo Cimento, 14: 171-1984.

“Majorana explicitly considers quantum mechanics as an irreducible statistical theory because the theory is not able to describe the time evolution of a single particle or atom in a precise environment at a deterministic level. This lack of determinism at the level of an elementary physical system motivated him to suggest a formal analogy between statistical laws observed in physics and in the social sciences.”