Ettore Majorana ( , ; 5 August 1906 – disappeared 25 March 1938) was an Italian theoretical physicist who worked on neutrino masses.
The Majorana equation, Majorana fermions, and Microsoft's device attempting to create topological qubits, Majorana 1, are named after him. In 2006, the Majorana Prize was established in his memory.
In 1938, Enrico Fermi was quoted as saying about Majorana: "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."
Majorana was a supporter of Italian fascism and a member of the National Fascist Party. Historical context indicates that after 1931, the Italian government required all university professors to swear an oath of loyalty to the Fascist regime to maintain their positions. He disappeared under mysterious circumstances after purchasing a ticket to travel by ship from Palermo to Naples. An investigation concluded in 2015 found evidence suggesting Majorana lived in Valencia, Venezuela, between 1955 and 1959. The case was officially closed with the conclusion that he had emigrated.
Life and work
Early and personal life
Majorana was born in Catania, Sicily. Majorana's uncle Quirino Majorana was also a physicist. Mathematically gifted, Majorana began his university studies in engineering in 1923, but switched to physics in 1928 at the urging of Emilio Segrè. 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.
Majorana was an enthusiastic and devout Catholic.
First published academic papers
thumb|200px|Handwritten notes for the equation in infinite components
Majorana's first papers dealt with problems in atomic spectroscopy. His first paper, published in 1928, was written when he was an undergraduate and it was coauthored by Giovanni Gentile, Jr., a junior professor at 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 on the phenomenon of autoionization in atomic spectra, which he called "spontaneous ionization"; an independent paper in the same year, published by Allen Shenstone of Princeton University, called it "auto-ionization", a name first used by Pierre Auger. This name, without the hyphen, has since become the conventional term for the phenomenon.
Majorana earned his Laurea in physics at the University of Rome La Sapienza in 1929. 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, also studied by I. I. Rabi and others, led to development of 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, written in Italian, it languished in relative obscurity for several decades.
Experiments in 1932 by Irène Joliot-Curie and Frédéric Joliot showed the existence of an unknown particle that they suggested was a gamma ray. Majorana was the first to interpret correctly the experiment as requiring a new particle that had a neutral charge and a mass about the same as the proton; this particle is the neutron. Fermi advised him to write an article on the topic, but Majorana did not. James Chadwick proved the existence of the neutron by experiment later that year, and he was awarded the Nobel Prize for this discovery.
Majorana was known for not seeking credit for his discoveries, considering his work to be trivial. He wrote only nine papers in his lifetime.
Work with Heisenberg and Bohr
"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. In letters he subsequently wrote to Heisenberg, Majorana revealed that he had found in him, not only a scientific colleague, but a warm personal friend."
In another letter from Copenhagen to a member of Enrico Fermi's group Giovannino, he expressed support for Nazi policies and applauded Hitler's sacking of civil servants from local administrations and his replacement of them with nationalist cadre:
Majorana recommended to his mother, who wanted to learn German, a newspaper that "became fascist overnight after Hitler imposed changes in the editorial board". implying that such measures were necessary to make room for a new generation. Majorana wrote: