Paul Dirac
Paul Adrien Maurice Dirac ( born August 8, 1902 in Bristol, † October 20, 1984 in Tallahassee ) was a British physicist, Nobel laureate and co-founder of quantum physics. One of his most important discovery is described in the Dirac equation in 1928, in Einstein's special theory of relativity and quantum physics were first brought together. He also laid the foundations for the subsequent detection of antimatter.
Life and work
Paul Adrien Maurice Dirac was born in Bristol, Gloucestershire, England. His father, Charles Dirac, was Swiss roots with the French-speaking Saint- Maurice, Valais. His mother, Florence Holten, was the daughter of a sailor from Cornwall. His childhood was due to the strict and authoritarian behavior of the father, the specialist French taught at Dirac's school, unhappy - a brother took his own life. Dirac studied electrical engineering in 1921 in Bristol, then switched to mathematics and got in 1923 a scholarship to the University of Cambridge, where he studied with Ralph Howard Fowler.
In 1925, he found in his dissertation the classical counterpart of the new quantum mechanical commutators of Heisenberg, Born and Jordan with the Poisson brackets of classical mechanics. In 1926, Paul Dirac an abstract version of quantum mechanics ( " transformation theory "), which contained the Heisenberg's matrix mechanics and Schrödinger's wave mechanics as special cases. Thus he could regardless of Schrödinger show the equivalence of both theories. Classical mechanics resulting in his theory as a special case of quantum mechanics. From Dirac also comes the introduction of the interaction picture, which used both the Schrödinger and Heisenberg picture.
In 1928, he presented on the basis of the work of Pauli exclusion principle on the on the eponymous Dirac equation, in which there is a relativistic, ie based on the special theory of relativity wave equation first order to describe the electron. Dirac found by emanated from the relativistic wave equation 2nd order of Charles Galton Darwin ( a further development of the Klein-Gordon equation) and a little " fiddling equations " with, that is, he sought an approach to a corresponding equation first order which could be obtained only with the introduction of spinors and Dirac matrices and their "square" again gives the relativistic wave equation. It provided, for example, a theoretical explanation for the anomalous Zeeman effect and the fine structure in atomic spectroscopy and explained the spin, which was known as a fundamental but misunderstood phenomenon previously in quantum mechanics, as a natural consequence of his relativistic wave equation. His equation also allowed Dirac to formulate the hole theory and the existence of the positron, the antiparticle of the electron to predict (but he shrank back before the first public postulation of a new particle and identified the negative antiparticle of the electron with the proton ). The positron was detected on 1932 of Anderson as new particles in cosmic rays. In the Dirac representation of quantum field theory, the vacuum is in analogy with solid state physics from one to the Fermi filled Dirac sea ( Dirac sea) of electrons. Pair production in the vacuum is the excitation of an electron from this Dirac sea on the Fermi addition - the surviving " hole" in the Dirac sea is the positron.
His 1930 book published The Principles of Quantum Mechanics ( German The principles of quantum mechanics, 1930) paved the way for the use of linear operators as a generalization ( " transformation theory " ) of the theories of Heisenberg and Schrödinger. With her the delta functional was (a special distribution, also Diracfunktion or delta function called ) and the Bra- Ket notation used in a state vector in the Hilbert space of a system (eg, the initial state) and the dual to him vector ( z. final state as in the description of the physical process ). The above-mentioned textbook remains to this day a standard work and was so perfect that he in his lectures simply from reading to in Dirac's eyes.
Dirac coined the term boson in recognition of the merits of Satyendra Nath Bose to the quantum statistics. He is with Enrico Fermi, the inventor of the statistics of the fermions ( Fermi -Dirac statistics ), but recognized Fermi's priority.
In 1931, he postulated as a first existence of a magnetic monopole, ie a particle with magnetic charge, similar to the electric charge, for example, the electron. The existence of such a particle which has not been observed, would explain the quantization of the electric charge. Behind ultimately stuck topological ideas that appear here for the first time in quantum mechanics.
In his "large number hypothesis" attempts Dirac - more plausible than similar attempts Eddington - to be a connection between the size of the fundamental constants and the current expansion of the universe. This gives rise to speculation about the temporal variation of fundamental constants, which will be investigated experimentally until now. Dirac's large competitor in the field of quantum mechanical formalism, Pascual Jordan, these ideas reached into its own theory of gravitation with variable gravitational constant.
In his study of the classical theory of radiating electrons from 1938 appeared next to " runaway solutions" for the first time Renormierungsideen on. The occurrence of divergent expressions in the usual renormalization theory of quantum electrodynamics, which are then made to disappear into the definition of "naked" charge and mass, but he refused life.
Dirac is also the inventor of many other formalisms of theoretical physics. Example comes from his original idea for path integrals, which were used as an alternative approach to quantum mechanics, but only " taken seriously " by Richard Feynman and expanded. In a work of 1949 he invented the "light cone quantization " ( light front formalism ) of quantum field theory, which is used in high energy physics a lot. In the 1950s, then Dirac tried to interpret the he postulated Dirac sea as universal ether.
He also studied in general Hamiltonian systems with " constraints" ( constraints ), especially in order to find an access to the quantization of gravity. These works later on in the BRST formulation. His study of extended systems in quantum field theory in 1962 is a precursor of p- branes and bag models of later years.
During the Second World War he worked on gas centrifuges for uranium enrichment.
From 1932 to 1969 he was professor of Luca -sian chair of mathematics at Cambridge University. He then worked at Florida State University in Tallahassee, Florida.
Honors
In 1933, Dirac was awarded together with Erwin Schrödinger the Nobel Prize in Physics "for the discovery of a new and useful form of the atomic theory." In 1930 he was elected as a member ( "Fellow" ) to the Royal Society, in 1939, the Royal Medal in 1952 and the Copley Medal awarded him. In 1952 he was awarded the Max Planck medal. In 1958 he was inducted into the Accademia Nazionale dei Lincei in Rome; The same year also saw the election as a member of the Leopoldina. In addition, he was awarded the British crown the Order of Merit.
In his honor, the Dirac Medal ( ICTP ) awarded to scientists for outstanding achievements as well as the Dirac Medal ( UNSW ) and the Dirac Medal ( IOP). After Paul Dirac also an asteroid is named.
Personality and views
Dirac was reserved by nature,. It did not bother him to be silent in society and to respond to questions very taciturn, strict truthfulness committed responses, of which many anecdotes were prevalent.
Dirac was a convinced atheist. When asked for his opinion on Dirac's views Wolfgang Pauli remarked in reference to the Islamic confession of God: " If I understand Dirac correctly, he says the following: There is no God and Dirac is his prophet. "
In 1937 he married Margit ( 1904-2002 ), the sister of the physicist Eugene Wigner. The mathematician Gabriel Andrew Dirac from his first marriage his wife was his stepson.