Paul Dirac English physicist, Nobel laureate in physics 1933 (together with E. Schrödinger) Date of Birth: 08.08.1902 Country: Great Britain

1. Biography of Paul Dirac
2. Contributions to Quantum Mechanics
3. Discovery of the Positron
4. Later Contributions and Honors

Biography of Paul Dirac

Paul Adrien Maurice Dirac, an English physicist, was born in Bristol, England. His father, Charles Adrien Ladislas Dirac, was a French language teacher at a private school, and his mother, Florence Hannah (Holten) Dirac, was English. Dirac initially attended a commercial school in Bristol and then studied electrical engineering at the University of Bristol, where he graduated in 1921 with a Bachelor of Science degree. During his time at university, Dirac became interested in Albert Einstein's theory of relativity and spent two years studying mathematics beyond the regular course. He then went on to pursue a Ph.D. in mathematics at St. John's College, Cambridge, and defended his doctoral dissertation in 1926. The following year, Dirac became a member of the scientific council at the same college.

Contributions to Quantum Mechanics

While Dirac was pursuing his Ph.D. at Cambridge, Werner Heisenberg and Erwin Schrödinger developed their formulations of quantum mechanics, applying the theory to describe the behavior of atomic and subatomic systems and the motion of particles such as electrons. Dirac began studying Heisenberg's and Schrödinger's equations as soon as they were published in 1925, making several valuable contributions. One of the limitations of quantum mechanics at the time was that it only applied to particles with low velocities compared to the speed of light, neglecting the effects described by Einstein's theory of relativity. Dirac aimed to introduce relativity into the wave equation, formulating it in a relativistic form. The equation he derived, now known as the Dirac equation, allowed for agreement with experimental data. Notably, the equation confirmed the existence of the electron's spin, which was previously only a hypothesis used to explain certain details of atomic spectra. Additionally, the Dirac equation predicted the magnetic properties of the electron.

Discovery of the Positron

Dirac's theory also indicated the existence of negative energies, which could not be interpreted within the scientific knowledge of the time. Instead of discarding negative energies as a "mathematical aberration" without physical meaning, Dirac concluded that states with negative energy were real. By considering the action of electromagnetic fields on an electron in a negative energy state, he discovered that the motion of the electron was equivalent to that of a positively charged particle. Dirac postulated that this positively charged particle could be the proton. Applying Wolfgang Pauli's exclusion principle, which states that only one electron can occupy each dynamic state, Dirac proposed that most of the negative energy states were already occupied, making them unobservable. However, a vacant energy state, similar to a hole in a uniform medium, could be observed and behaved like a positively charged electron. Furthermore, since the energy of this hole corresponded to the lack of negative energy, it was positive, similar to the energy of all known particles. Thus, Dirac predicted the existence of an antiparticle, the positron, which was later discovered in 1932 by Carl D. Anderson.

Later Contributions and Honors

Dirac's work extended beyond the discovery of the positron. He also showed that an electron could occupy a vacant hole, equivalent to the collision between an electron and an antielectron, resulting in the annihilation of both particles and the release of energy in the form of photon radiation. Dirac also speculated that other particles, such as the proton, should have their antimatter counterparts, but describing such particle-antiparticle pairs would require a more complex theory. The existence of the antiproton was experimentally confirmed in 1955 by Owen Chamberlain, and many other antiparticles have since been discovered. Dirac's contributions to theoretical physics also included his work on the statistical distribution of energy in electron systems, known as Fermi-Dirac statistics. This work was crucial in understanding the electrical properties of metals and semiconductors. Dirac further explored the possibility of the existence of magnetic monopoles, isolated positive or negative magnetic particles, similar to positively or negatively charged particles. However, experimental efforts to detect magnetic monopoles have not been successful thus far.

In addition to receiving the Nobel Prize in Physics in 1933 jointly with Erwin Schrödinger for their discovery of new productive forms of atomic theory, Dirac was awarded the Royal Medal in 1939 and the Copernicus Medal in 1952 by the Royal Society. He became a foreign member of the National Academy of Sciences in 1949 and a member of the Pontifical Academy of Sciences in 1961. In 1973, Dirac was honored with the Order of the British Empire for his services. After retiring from Cambridge in 1968, he joined the faculty at the University of Florida, where he remained until his passing in Tallahassee in 1984. Dirac married Margit Wigner, the sister of physicist Eugene Wigner, in 1937, and they had two daughters. Dirac was known as a quiet, introverted, and reserved individual who preferred to work alone, and he had few direct students. He enjoyed taking long walks.