Ettore Majorana (/ˌmædʒəˈrænə/, Italian: [ˈɛttore
majoˈraːna]; born on 5 August 1906 – probably died after 1959) was an Italian
theoretical physicist who worked on neutrino masses. On March 25, 1938, he
disappeared under mysterious circumstances while going by ship from Palermo to
Naples. The Majorana equation and Majorana fermions are named after him. In
2006, the Majorana Prize was established in his memory.
Life and work
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 about Majorana, Rome 1938,)
Gifted in mathematics
Majorana was born in Catania, Sicily. Mathematically 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. 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 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 on 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.
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 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.
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 told him to write an article,
but Majorana didn't bother. 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 banal. He wrote only nine papers in his
lifetime.
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. 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." The Nazis had
come to power in Germany as Majorana arrived there. He 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 also travelled to Copenhagen, where he worked with
Niels Bohr, another Nobel Prize winner, and a friend and mentor of Heisenberg.
"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."
During these years, in which he published few articles,
Majorana wrote many small works on geophysics, electrical engineering,
mathematics, and relativity. These unpublished papers, preserved in Domus
Galileiana in Pisa, recently have been 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 of
his "high fame of singular expertise reached in the field of theoretical
physics", independently of the competition rules.
Majorana's last-published paper, in 1937, this time in
Italian, was an elaboration of a symmetrical theory of electrons and positrons.
In 1937, Majorana predicted that in the class of particles
known as fermions there should be particles that are their own antiparticles.
This is the so-called Majorana fermion.
Solution of Majorana's equation yields particles that are
their own anti-particle, now referred to as Majorana Fermions. In April 2012,
some of what Majorana predicted may have been confirmed in experiments on
hybrid semiconductor-superconductor wire devices. These experiments may potentially lead to a
better understanding of quantum mechanics and may help build a quantum
computer. There has also been speculation that at least some part of the
"missing mass" in the universe, which cannot be detected except by
inference of its gravitational influences, may be composed of Majorana
particles.
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 suggested explanations
Majorana disappeared in unknown circumstances during a boat
trip from Palermo to Naples on 25 March 1938. Despite several investigations,
his body was not found and his fate is still uncertain. He had apparently
withdrawn all of his money from his bank account prior to making his trip to
Palermo. 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. On the day of his
disappearance, Majorana sent the following note to Antonio Carrelli, Director
of the Naples Physics Institute:
Dear Carrelli,
I made a decision that
has become unavoidable. There isn't a bit of selfishness in it, but I realize
what trouble my sudden disappearance will cause you and the students. For this
as well, I beg your forgiveness, but especially for betraying the trust, the
sincere friendship and the sympathy you gave me over the past months.
I ask you to remember
me to all those I learned to know and appreciate in your Institute, especially
Sciuti: I will keep a fond memory of them all at least until 11 pm tonight,
possibly later too.
E. Majorana
This was followed rapidly by a telegram cancelling his
earlier plans. He apparently bought a ticket from Palermo to Naples and was
never seen again.
Several possible
explanations for his disappearance have been proposed, including:
Hypothesis of suicide
Proposed by his colleagues Amaldi, Segrè and others
Hypothesis of escape
to Argentina
Proposed by Erasmo Recami and Carlo Artemi (who has
developed a detailed hypothetical reconstruction of Majorana's possible escape
and life in Argentina)
Hypothesis of escape
to Venezuela
Proposed the Rai 3 talk show "Chi l'ha Visto?"
published a statement stating that Majorana was alive between 1955 and 1959,
living in Valencia, Venezuela.
Hypothesis of escape
to a monastery
Proposed by Sciascia (putatively the Charterhouse of Serra
San Bruno)
Hypothesis of
kidnapping or murder
By Bella, Bartocci, and others, to avoid his participation
in the construction of an atomic weapon
Hypothesis of escape
to become a beggar
By Bascone and Venturini (called the "omu cani" or
"dog man" hypothesis)
Extended summaries
and investigations
The Italian writer Leonardo Sciascia has summarized some of
the results of these investigations and these hypotheses, however, some of
Sciascia's conclusions were refuted by some of Majorana's former colleagues,
including E. Amaldi and E. Segrè.
Recami critically examines various hypotheses for Majorana's
disappearance who various rival explanations concerning Majorana's
disappearance, including those advanced by Sciascia, and presents suggestive
evidence for the proposal that Majorana travelled to Argentina.
Italian philosopher Giorgio Agamben has also recently
published a book that examines the case of Majorana's disappearance.
Case reopened by Rome Attorney's Office and closed with
presumed emigration to Venezuela
In March 2011, Italian media reported that the Rome
Attorney's Office had announced an inquiry into the statement made by a witness
about meeting with Majorana in Buenos Aires in the years after World War II. On 7 June 2011 Italian media reported that the
Carabinieri's RIS had analyzed a photograph of a man taken in Argentina in
1955, finding ten points of similarity with Majorana's face.
On 4 February 2015, the Rome Attorney's Office released a
statement declaring that Majorana was alive between 1955–1959, living in
Valencia, Venezuela. These last
findings, based on new evidence, made the Office declare the case officially
closed, having found no criminal evidence related to his disappearance which
probably was a personal choice.
Commemoration of
centenary
The year 2006 marked
Majorana's centenary.
An international conference on "Ettore Majorana's
legacy and the Physics of the XXI century" was held in commemoration of
the centennial of Majorana's birth in Catania, October 5–6, 2006. The conference proceedings with articles of
highly 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 Antonino 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 of his nine collected papers, with
commentary and English translations, was published by the Italian Physical
Society in 2006.
Also to commemorate the centenary, the journal, Electronic
Journal of Theoretical Physics] (EJTP), published a special issue of twenty
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)
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