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Ettore Majorana

Ettore Majorana (English pronunciation: /ˈmaɪ.ɔrɑːnə/ my-or-ah-nə; 5 August 1906 – 27 March 1938 (presumed dead)) was an Italian theoretical physicist who began promising work on neutrino masses. He disappeared suddenly in mysterious circumstances. He is noted for the eponymous Majorana equation.

Life and work

Gifted in mathematics

Majorana was born in Catania, Sicily. Mathematically extremely gifted, he was very young when he joined Enrico Fermi's team in Rome as one of the "Via Panisperna boys", who took their name from the street address of their laboratory.

His uncle Quirino Majorana was also a physicist.

He began his university studies in engineering in 1923 but switched to physics in 1928 at the urging of Emilio Segrè.[1] His first papers dealt with problems in atomic spectroscopy.

First published academic papers

His first paper, published in 1928, was written when he was an undergraduate and was coauthored by Giovanni Gentile Jr., a junior professor in the Institute of Physics in Rome. This work was an early quantitative application to atomic spectroscopy of Fermi's statistical model of atomic structure (now known as the Thomas-Fermi model, due to its contemporaneous description by Llewellyn Thomas).

In this paper, Majorana and Gentile performed first-principles calculations within the context of this model that gave a good account of experimentally observed core electron energies of gadolinium and uranium, and of the fine structure splitting of caesium lines observed in optical spectra. In 1931, Majorana published the first paper describing the phenomenon of autoionization in atomic spectra, designated by him as "spontaneous ionization"; an independent paper in the same year, published by Allen Shenstone of Princeton University, designated the phenomenon as "auto-ionization", a name first used by Pierre Auger. This name has since become conventional, without the hyphen.

Majorana earned his undergraduate degree in engineering and completed his physics doctorate, both at the University of Rome La Sapienza.[1]

In 1932 he published a paper in the field of atomic spectroscopy concerning the behaviour of aligned atoms in time-varying magnetic fields. This problem, which was also studied by I.I. Rabi and others, led to an important sub-branch of atomic physics, that of radio-frequency spectroscopy. In the same year Majorana published his paper on a relativistic theory of particles with arbitrary intrinsic momentum, in which he developed and applied infinite dimensional representations of the Lorentz group, and gave a theoretical basis for the mass spectrum of elementary particles. Like most of Majorana's papers in Italian, it languished in relative obscurity for several decades. (It is discussed in detail by D. M. Fradkin, Amer. J. Phys., vol. 34, pp. 314–318 (1966)).

He was the first to propose the hypothesis that the unknown particle involved in the experiment of Irène Curie and Frédéric Joliot should not only be neutral but have a mass about the same as the proton: he was inventing the neutron. When he explained this to Fermi, Fermi told him to write an article about this, but Majorana didn't bother, and the credit for this interpretation was given to James Chadwick (who was awarded the Nobel Prize for this discovery).[2]

Majorana was known for not seeking credit for his discoveries, considering his work to be banal.

Work with Heisenberg, illness, isolation

"At Fermi's urging, Majorana left Italy early in 1933 on a grant from the National Research Council. In Leipzig, Germany, he met Werner Heisenberg, another Nobel Prize winner. In the letters he subsequently wrote to Heisenberg, Majorana revealed that he had found in him not only a scientific colleague but a warm personal friend."[3] Majorana also travelled to Copenhagen, where he worked with Niels Bohr, another Nobel Prize winner, and friend and mentor of Heisenberg.

The Nazis had come to power in Germany as Majorana arrived there. He studied with Werner Heisenberg in Leipzig, and worked on a theory of the nucleus (published in German in 1933) which, in its treatment of exchange forces, represented a further development of Heisenberg's theory of the nucleus. Majorana's last-published paper, in 1937, this time in Italian, was an elaboration of a symmetrical theory of electrons and positrons.

"In the fall of 1933, Majorana returned to Rome in poor health, having developed acute gastritis in Germany and apparently suffering from nervous exhaustion. Put on a strict diet, he grew reclusive and became harsh in his dealings with his family. To his mother, with whom he had previously shared a warm relationship, he had written from Germany that he would not accompany her on their customary summer vacation by the sea. Appearing at the institute less frequently, he soon was scarcely leaving his home; the promising young physicist had become a hermit. For nearly four years he shut himself off from friends and stopped publishing."[3]

During these years, in which he published few articles, Majorana wrote many small works on several topics: from Geophysics, to Electrical Engineering, from Mathematics to the Relativity. These unpublished papers, preserved in Domus Galileiana in Pisa, have been recently edited by Erasmo Recami and Salvatore Esposito.

He became a full professor of theoretical physics at the University of Naples in 1937, without needing to take an examination because, as certified by official documents, the competition board suggested that they appoint Majorana as full professor of Theoretical Physics in a University of the Italian kingdom because of his "high fame of singular expertise reached in the field of theoretical physics",[4] independently of the competition rules.

The competition board's suggestion was accepted and Majorana obtained the chair of Theoretical Physics in Naples. After a few months of teaching, however, his tenure of the post ended with his well-known disappearance.

Work on neutrino masses

Majorana did prescient theoretical work on neutrino masses, a currently active subject of research. He also worked on an idea that mass may exert a small shielding effect on gravitational waves, which did not gain much traction.

Disappearance at sea and theories

Majorana disappeared in unknown circumstances during a return boat trip from Palermo to Naples. Despite several investigations, the truth about his fate is still uncertain. His body has not been found. He had apparently withdrawn his salary money from his bank account, prior to making a trip to Palermo.[4] He may have travelled to Palermo hoping to visit his friend Emilio Segrè, a professor at the university there. But Segrè was in California at that time, September 1938, and as a Jew, was barred from returning to Italy under a 1938 law passed by Benito Mussolini's government. On March 25, 1938 Majorana wrote a note to Antonio Carrelli, Director of the Naples Physics Institute, asking to be remembered to his colleagues and saying that he had made an unavoidable decision and apologising for the inconvenience that his disappearance would cause. This was followed rapidly by another rescinding his earlier plans. He apparently bought a ticket from Palermo to Naples and was never seen again.[4]

Several possible explanations for his disappearance have been proposed, including:

Hypothesis of suicide, by his colleagues Amaldi, Segrè and others
Hypothesis of escape to Argentina, by Erasmo Recami and Carlo Artemi (who has developed a detailed if hypothetical reconstruction of Majorana's possible escape and life in Argentina)
Hypothesis of escape to a monastery, by Sciascia
Hypothesis of kidnapping or killing, to avoid his participation in the construction of an atomic weapon, by Bella, Bartocci and others
Hypothesis of escape to become a beggar ("omu cani" hypothesis), by Bascone

The Sciascia hypothesis

The Italian writer Leonardo Sciascia has summarized some of the results of these investigations and these hypotheses in his passionate book La Scomparsa di Majorana (Einaudi, 1975 - English translation: The Moro Affair and The Mystery of Majorana, Carcanet, 1987, ISBN 0-85635-700-6). However, some of Sciascia's conclusions were refuted by certain of Majorana's former colleagues, including E. Amaldi and E. Segrè. The various hypotheses on Majorana's disappearance have been extensively discussed by Erasmo Recami in his book "Il caso Majorana: Lettere, testimonianze, documenti" (Di Renzo Editore, Roma, 2000), and in a journal article (E. Recami, "I nuovi documenti sulla scomparsa del fisico Ettore Majorana", Scientia, vol. 110, pp. 577–588 (1975); English version titled "New Evidence on the Disappearance of the Physicist Ettore Majorana", Scientia, vol. 110, p. 589 ff. (1975)). In the above-mentioned book and article, Recami discusses critically the various rival explanations concerning Majorana's disappearance, including those advanced by Sciascia in his short book, and presents highly suggestive evidence to the effect that Majorana absconded to Argentina, where he may have earned his living as an engineer.

Reopening of the case

On March, 2011, Italian media say Rome Attorney's office announced to have started an inquiry later on the statement made by a witness about the meeting with Majorana in Buenos Aires in the years after World War II.[5][6]

Commemoration of Majorana's centenary

The year 2006 marked Majorana's centenary.

The International Conference on "Ettore Majorana's legacy and the Physics of the XXI century" EMC2006 was held in commemoration of the centennial of Majorana's birth in Catania October 5–6, 2006. The conference Proceedings with articles of high ranked international scientists A. Bianconi, D. Brink, N. Cabibbo, R. Casalbuoni, G. Dragoni, S. Esposito, E. Fiorini, M. Inguscio, R.W. Jackiw, L. Maiani, R. Mantegna, E. Migneco, R. Petronzio, B. Preziosi, R. Pucci, E. Recami, and A. Zichichi have been published by POS Proceedings of Science of SISSA Edited by Andrea Rapisarda (chairman), Paolo Castorina, Francesco Catara, Salvatore Lo Nigro, Emilio Migneco, Francesco Porto and Emanuele Rimini.

A commemorative book "Ettore Majorana Scientific Papers on the occasion of the centenary of the birth" of his (nine) collected papers, with commentary and English translations, was published by the Italian Physical Society.

To commemorate the centenary Electronic Journal of Theoretical Physics' (EJTP) also published a special issue of 20 articles dedicated to the modern development of Majorana’s legacy.

The Electronic Journal of Theoretical Physics also established a prize in his memory to mark the centenary. The "Majorana Medal" or Majorana Prize is an annual prize for researchers who have shown peculiar creativity, critical sense and mathematical rigour in theoretical physics — in its broadest sense. The recipients of the 2006 Majorana Prize were Erasmo Recami (University of Bergamo and INFN) and George Sudarshan (University of Texas); of the 2007 Majorana Prize: Lee Smolin (Perimeter Institute for Theoretical Physics, Canada), Eliano Pessa (Centro Interdipartimentale di Scienze Cognitive, Università di Pavia and Dipartimento di Psicologia, Università di Pavia Piazza Botta, Italy) and Marcello Cini (Dipartimento di Fisica, Università La Sapienza, Roma, Italy).
[edit] Quote

The following quote is reported to Giuseppe Cocconi, and attributed to Enrico Fermi.[7]
“ There are many categories of scientists, people of second and third rank, who do their best, but do not go very far. There are also people of first class, who make great discoveries, which are of capital importance for the development of science. But then there are the geniuses, like Galileo and Newton. Well, Ettore was one of these. Majorana had greater gifts than anyone else in the world; unfortunately he lacked one quality which other men generally have: plain common sense. ”