Paul Adrien Maurice Dirac
"Physical Laws should have mathematical beauty." This statement was Dirac's response to
the
question of his philosophy of physics, posed to him in Moscow in 1955. He wrote it on a
blackboard that is still preserved today.[1]
Paul Adrien Maurice Dirac (1902-1984), known as P. A. M. Dirac, was the fifteenth
Lucasian Professor of Mathematics at Cambridge. He shared the Nobel Prize for Physics in
1933
with Erwin Schrodinger.[2] He is considered to be the founder of quantum mechanics,
providing
the transition from quantum theory. The Cambridge Philosophical Society awarded him the
Hopkins Medal in 1930. He was awarded the Royal Medal by the Royal Society of London in
1939 and the James Scott Prize from the Royal Society of Edinburgh. In 1952 the Max
Plank
Medal came from the Association of German Physical Societies, as well as the Copley
Medal
from the Royal Society. The Akademie der Wissenschaften in the German Democratic
Republic
presented him with the Helmholtz Medal in 1964. In 1969 he received the Oppenheimer
Prize
from the University of Miami. Lastly in 1973, he received the Order of Merit.[3]
Dirac was well known for his almost anti--social behavior, but he was a member of many
scientific organizations throughout the world. Naturally, he was a member of the Royal
Society,
but he was also a member of the Deutsche Akademie der Naturforsher and the Pontifical
Academy of Sciences. He was a foreign member of Academie des Sciences Morales et
Politiques and the Academie des Sciences, the Accademia delle Scienze Torino and the
Accademia Nazionale dei Lincei and the National Academy of Science. He was an honorary
member and fellow of the Indian Academy of Science, the Chinese Physical Society, the
Royal
Irish Academy, the Royal Society of Edinburgh, the National Institute of Sciences in
India, the
American Physical Society, the Tata Institute for Fundamental Research in India, the
Royal
Danish Academy, and the Hungarian Academy of Sciences. He was a corresponding member of
the USSR Academy of Sciences.[4] The world wide respect he earned for his work was well
deserved.
A prolific writer, Dirac published over two hundred works between 1924 and 1987,
mainly papers in physics journals on topics relating to quantum mechanics. His book
Principles
of Quantum Mechanics , published in 1930, was the first textbook in the discipline and
became
the standard.[5] Some predictions made by Dirac are still untested because his
theoretical work
was so far reaching, but many other predictions have been verified, assuring him of a
special
place in the history of physics.[6]
Dirac was three years old when Einstein published his famous papers on relativity in
1905 and a year old when his predecessor Joseph Larmor began his tenure as Lucasian
professor.
Physics had just begun its incredible transformation of the twentieth century when Dirac
arrived
on the scene.
Dirac came to Cambridge as a graduate student in 1923 after graduating from the
University of Bristol. As a student in mathematics in St. John's College, he took his
Ph.D. in
1926 and was elected in 1927 as a fellow. His appointment as university lecturer came in
1929.[7] He assumed the Lucasian professorship following Joseph Larmor in 1932 and
retired
from it in 1969. Two years later he accepted a position at Florida State University where
he lived
out his remaining years. The FSU library now carries his name. [8]
While at Cambridge, Dirac did not accept many research students. Those who worked
with him generally thought he was a good supervisor, but one who did not spend much time
with
his students. A student needed to be extremely independent to work under Dirac.[9] One
such
student was Dennis Sciama, who later became the supervisor of Stephen Hawking, the
current
holder of the Lucasian Chair. Dirac's lectures were attended by Sir M. J. Lighthill while
he was a
student at Cambridge and Lighthill was Dirac's successor to the Lucasian Chair.
Dirac offered the first course in quantum mechanics in Britain, entitled Quantum Theory
(Recent
Developments) . Among his students was J. R. Oppenheimer, an American, who later on was
in
charge of the Manhattan Project, which created the first atomic bomb.[10]
Dirac's work should be understood in the context of the development of quantum physics.
The theoretical work had been underway for several years before his entry into the field.
It was
plagued with difficulties, in part because of the radical change in the way one thought
about the
world around us, and in part because it was a difficult problem. The important
developments of
the beginning of this century were carried out by Max Plank, Max Born, Niels Bohr,
Albert
Einstein, Werner Heisenberg, Erwin Schrodinger, and Wolfgang Pauli. Quantum mechanics
was
brought to life during the few short years of 1925 through 1927 by most of these men.[11]
Dirac was the first to apply quantum mechanics to an electromagnetic field, using the
method of second quantization. This work contained the basis for quantum field
theory,[12]
which Dirac called quantum electrodynamics.[13] The singular delta function was invented
by
Dirac in order to prove two problems were equivalent. He was working with the problems
of
"diagnolizing the energy matrix in the Born--Heisenberg-Jordan theory" and "finding the
energy
eigenvalues of Schrodinger's wave equation."[14] The delta function is now used in many
different areas of mathematics and physics and is considered basic. In 1926 he derived
Balmer-spectrum energy levels of the hydrogen atom. He was the first to derive the
Lorentzian
shape of spectral lines using quantum mechanics. He introduced the terms bra and ket from
the
word bracket to denote the use of parts of the bracket. The half brackets were for state
vectors
and their eigenvalues. One of his major breakthroughs was the use of an algebraic version
of
quantum mechanics based on Poisson brackets.
Dirac's life was dedicated to physics with no interests outside of his work, but,
besides
quantum mechanics, he did work on isotope separation, magnetic monopoles, large-number
hypothesis and other physics areas. The large-number hypothesis was based on Dirac's
belief that
very large constants should not exist in nature. Somehow these large constants that did
exist
were a consequence of the age of the universe.[15] One of the interesting implications of
his
work that predicted the positron was the prediction of a magnetic monopole. It is common
knowledge that a magnet has a north and a south pole, where opposites attract and
sameness
repels. The idea that a pole could exist in isolation is quite foreign. Although theory
predicts its
existence, none has ever been found. His work in isotope separation was a step from his
theoretical world into the world of experimental physics. He had done some work in the
1930s,
but stopped when his colleague, Peter Kapitza, found himself unable to leave the Soviet
Union,
because Stalin had revoked the necessary exit permit.[16]
In the 1940s the war effort dragged Dirac back into isotope separation. A group at Oxford
was
looking for an efficient means to do it. Dirac's method worked, but it was not considered
the
most cost effective. However, he did continue to contribute to the effort, and even wrote
a report
on the statistical method of isotope separation that contained concepts still used
today.[17]
Dirac views on religion were very restricted. He seemed to have believed that nothing was
as
important as his physics. Heisenberg related a story of an exchange between Dirac and
Wolfgang
Pauli where Dirac expressed his agnostic views. Pauli responded with "Dirac has a new
religion.
There is no God and Dirac is his prophet."[18] Dirac was a member of the Pontifical
Academy of
Sciences at the Vatican, having written many papers for them. He was not anti-religious.
His
wife maintained that he was deeply religious, but he has shown no evidence for it.[19]
|