Ettore Majorana was an Italian theoretical physicist. He was known for his work on neutrino masses.
Background
Ettore Majorana was born on August 5, 1906, in Catania, Sicilia, Italy. He was the fourth of the five children of Fabio Massimo Majorana, an engineer and inspector general of the Italian ministry of communications, and Dorina Corso. At the age of four, he revealed the first signs of a gift for arithmetic. His uncle Quirino Majorana was also a physicist.
Education
After schooling at home, Ettore Majorana entered the Jesuit Massimiliano Massimo Institute in Rome and completed his secondary school education at the Liceo Torquato Tasso, passing his maturità classica in the summer of 1923. That fall he entered the School of Engineering of the University of Rome, where his fellow students included his older brother Luciano, Emilio Segrè, and Enrico Volterra, later professor of civil engineering at the University of Houston. Majorana was persuaded by Segré to take up physics at the beginning of 1928. His lively mind, insight, and the range of his interests immediately impressed the new circle of physicists that had formed around Fermi. He was nicknamed “the Grand Inquisitor” for his exceptionally penetrating and inexorable capacity for scientific criticism, even of his own person and work. He received the doctorate in physics on 6 July 1929 with a thesis on the mechanics of radioactive nuclei sponsored by Fermi.
Fermi convinced Ettore Majorana to go abroad financed by a grant from the Consiglio Nazionale delle Ricerche; and Majorana began his journey at the end of January 1933, traveling first to Leipzig and then to Copenhagen. In Leipzig, Heisenberg persuaded Majorana to publish his paper on nuclear forces. He returned to Rome in the autumn of 1933 in poor health aggravated by gastritis, which he had developed in Germany and which was attributed by some to nervous exhaustion. He attended the Istituto di Fisica at intervals but stopped after a few months, despite his friends’ attempts to lead him back to a normal life.
Appointed professor of theoretical physics at Naples in November 1937, Majorana soon discovered that his course was too advanced for the majority of students. On 25 March 1938 he wrote from Palermo to his colleague and friend Antonio Carrelli that he found life in general, and his own in particular, useless and had decided to commit suicide. A few hours later he sent a telegram to Carrelli asking him to disregard the letter and boarded a steamer for Naples that evening. Although he was seen at daybreak as the ship entered the Bay of Naples, no trace was ever found of him, despite an inquiry continued for several months and repeated appeals of his family published in the Italian press.
Majorana’s total scientific production consists of nine papers, which can be divided into two parts: six papers on problems of atomic and molecular physics, and three on nuclear physics or the properties of elementary particles. The first group of papers deals with the splitting of Roentgen terms of heavy elements induced by electron spin, the interpretation of recently observed spectral lines in terms of atomic states with two excited electrons, the formation of the molecular ion of helium, the binding of molecular hydrogen through a mechanism different from that of Walter Heitler and Heinz London, and the probability of reversing the magnetic moment of the atoms in a beam of polarized vapor moving through a rapidly varying magnetic field. The last paper remains a classic on nonadiabatic moment-inversion processes. Often quoted, it provides the basis for interpreting the experimental method of flipping neutron spin with a radio-frequency field. The other papers of this period (1928-1932) reveal a thorough knowledge of experimental data and ease - particularly unusual at the time - in using the symmetry properties of the states to simplify problems or to choose the most suitable approximation for solving each problem quantitatively. The latter ability was at least partly due to Majorana’s exceptional gift for calculation.
Majorana was an enthusiastic and devout Catholic. The hypothesis shared by his family and others who had the privilege of knowing him (Enrico Fermi’s wife Laura was one of the few) is that he withdrew to a monastery after his mysterious disappearance.
Views
Majorana’s major scientific contribution is found in the last three papers. “Sulla teoria dei neclie” (1932) concerns the theory of light nuclie under the assumption that they consist solely of protons and neutrons that interact through exchange forces acting only on the space coordinates (and not on the spin), so that the alpha particle - rather than the deuteron - is shown to be, as it is, the system with greatest binding energy per nucleon. The essential work on this paper was completed in the spring of 1932, only two months after the appearance of J. Chadwick’s letter to the editor of Nature announcing the discovery of the neutron. Fermi and his friends tried in vain to persuade Majorana to publish, but he did not consider his work good enough and even forbade Fermi to mention his results at an international conference that was to take place in July 1932 in Paris. The July 1932 issue of Zeitschrift für Physik contains the first of Heisenberg’s three famous papers on the same subject. They are based on Heisenberg’s exchange forces, which differ from Majorana’s forces in that not only the space coordinates but also the spin of the two particles are exchanged.
“Teoria relativistica di particelle con momento intrinseco arbitrario” (1932), the first paper of Majoranan’s second phase, concerns the relativistic theory of particles with arbitrary intrinsic angular momentum. Although in some ways outside the mainstream of the development of elementary particle physics, it represents the first attempt to construct a relativistically invariant theory of arbitrary half-integer or integer-spin particles. Majorana’s mathematically correct theory contains the first recognition, and the simplest development and application, of the infinite-dimensional unitary representations of the Lorentz group. This theory lies outside the mainstream of successive development primarily because, from the outset, Majorana set himself the task of constructing a relativistically invariant linear theory of which the eigenvalues of the mass were all positive. This viewpoint was justified at the time the paper was written (summer 1932), since news of C. D. Anderson’s discovery of the positron had not yet reached Rome.
Majorana’s last paper was written in 1937 on Fermi’s urging, after four years of not publishing because of poor health. It contains a symmetrical theory of the electron and the positron based on the Dirac equation but in which the states of negative energy are avoided and a neutral particle is identical to its antiparticle. The most characteristic point is the discovery of a representation of the Dirac matrices γk (k = 1, 2, 3, 4), in which the first three components are real, the fourth imaginary, like the vector (Majorana representation).
At the present, no neutral particle of the type suggested by Majorana is known, since it has been experimentally established that the neutron, lambda particle, and neutrino differ from their corresponding antiparticles. Nevertheless, Majorana’s neutrino, vM characterized by the equality νM = ν̄M (the bar indicated the antiparticle), has played an important part in the physics of weak interactions, especially since the discovery by T. D. Lee and C. N. Yang of the nonconservation of parity and the development of the two-component theory, of the neutrino. This theory is related to that of Majorana, to which, in certain aspects, it is equivalent. Contrary to the two-component theory, Majorana’s does not require the neutrino to have a mass exactly equal to zero, and a small neutrino mass cannot at present be excluded on the basis of available experimental data.
Membership
Boys from via Pansperna
,
Italy
Personality
Majorana had an extraordinary gift for mathematics, an exceptionally keen analytic mind, and an acute critical sense. It was perhaps the latter, together with a certain lack of balance on the human side, that interfered with his capacity for creative synthesis and prevented him from reaching a level of scientific productivity comparable to that attained at the same age by major contemporary physicists. Yet his choice of problems and his way - especially his mathematical methods - of attacking them showed that he was naturally in advance of his times and, in some cases, almost prophetic.
Quotes from others about the person
"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." - Enrico Fermi.
"I have no hesitation to state to you, and I am not saying this as a hyperbolic statement, that of all Italian and foreign scholars that I have had the opportunity to meet, Majorana is among all of them the one that has most struck with for his deep brilliance." - Enrico Fermi in his letter to Benito Mussolini.
"Oh, he was really a genius, perhaps like Einstein, but Einstein was normal." - Sebastiano Sciuti, Majorana's student.
Connections
Ettore Majorana was not married and had no children, at least before his mysterious disappearance.
Neutrino Man: The Vanishing of Ettore Majorana
Eighty years of speculation have not solved the disappearance of the Italian physicist Ettore Majorana in 1938. Many theories, some insanely wild, have been advanced concerning the disappearance of Majorana, who has become far more famous in death than in life.
Ettore Majorana: Unveiled Genius and Endless Mysteries
This biography sheds new light on the life and work of physicist Ettore Majorana (including unpublished contributions), as well as on his mysterious disappearance in March 1938.