Abdus Salam

Abdus Salam

Pakistani theoretical physicist, winner of the 1979 Nobel Prize in Physics
Date of Birth: 29.01.1926
Country: Pakistan

Content:
  1. Biography of Abdus Salam
  2. Unified Theory of Forces
  3. Contributions to Particle Physics
  4. Later Career and Honors

Biography of Abdus Salam

Pakistani theoretical physicist, Abdus Salam, was born in the rural town of Jhang and was the son of Mohammad Hussain, a civil servant in the district education department, and Hajira Hussain. Salam studied at Government College, Punjab University in Lahore, graduating in 1946 with a Bachelor's degree. He then received a special scholarship to attend St. John's College, Cambridge University in England, where he graduated with a Master's degree with First Class Honours in Mathematics and Physics in 1949. He remained in Cambridge and defended his doctoral dissertation in theoretical physics at the Cavendish Laboratory in 1952, which focused on quantum electrodynamics. After the publication of his dissertation, it gained attention from the international physics community. In 1951, Salam became a professor of mathematics at Government College. Initially, he intended to establish a school of theoretical physicists in Pakistan, but soon realized that he would not be able to successfully pursue theoretical physics while living so far away from leading research centers in Europe, and in 1954, he returned to Cambridge as a lecturer in mathematics. Since 1957, Salam has held the chair of theoretical physics at Imperial College in London. He is also the director of the International Centre for Theoretical Physics in Trieste, Italy, founded in 1964 to promote the work of scientists from developing countries.

Unified Theory of Forces

In the mid-1950s, Salam attempted to develop a unified theory of all forces observed in nature, aiming to solve a problem dating back to the 19th century. In the 1870s, Scottish mathematician and physicist James Clerk Maxwell constructed a unified theory of electricity and magnetism, reducing them to a single interaction - electromagnetism. Subsequently, physicists tried to build a theory that encompassed not only electromagnetism but also gravity, as well as strong and weak interactions (strong interaction holds protons and neutrons, which form the nucleus of an atom, together; weak interaction repels them). Both strong and weak interactions significantly differ from previously known forces. While gravity and electromagnetism have unlimited range, strong interaction is only effective at distances not exceeding the size of an atomic nucleus, and weak interaction is felt at even smaller distances. The new theoretical ideas, for which Salam, Sheldon L. Glashow, and Steven Weinberg were awarded the Nobel Prize, led to the construction of a theory that unified electromagnetism and weak interaction. Similar to Maxwell's unification of electricity and magnetism, the Salam-Glashow-Weinberg theory presented electromagnetism and weak interaction as different aspects of a single "electroweak" interaction.

Contributions to Particle Physics

In the early 1960s, both Salam and Glashow independently attempted to unify electromagnetism and weak interaction based on the concept of gauge symmetry. Under gauge symmetry, properties or relationships remain unchanged when the scale or origin of relative measurement is altered. In 1954, Yang Chen-Ning and Robert L. Mills, working at the Brookhaven National Laboratory, unsuccessfully tried to generalize the principle of gauge symmetry to include strong interaction. However, their findings served as a stimulus for the subsequent work of Salam, Glashow, and Weinberg.

Salam and Weinberg, working independently and using Sheldon Glashow's gauge symmetry, published their respective theories of weak and electromagnetic interactions in 1968 and 1967. Salam and Weinberg proposed a new mechanism that endowed mass to the W±, W–, and Z0 particles while leaving photons massless. The main idea of this mechanism, called spontaneous symmetry breaking, originated from solid-state physics. Salam explained the essence of his idea with the following example: imagine a group of people having a meal around a round table. The table is set in such a way that there is a plate in front of each chair, and napkins are arranged around the perimeter of the table, between the plates. The table setting is symmetrical (a napkin is placed on the right and left of each person), but if one of the individuals takes a napkin, the symmetry is broken. If everyone at the table takes a napkin, the symmetry can be broken or maintained. Although choosing either the right or left napkin is equally acceptable, symmetry will be restored only if everyone at the table makes the same choice (i.e., everyone chooses the napkin on their right or everyone chooses the napkin on their left). Otherwise, someone at the table will be left without a napkin, and somewhere else on the table, one napkin will remain unused, creating an obvious asymmetry. Salam hypothesized that the gauge symmetry, which connects electromagnetic and weak interactions, is spontaneously broken when the energy level changes significantly. At very high energies, these two interactions are indistinguishable. In these conditions, the masses of the W and Z particles (and hence weak interactions) do not pose any difficulties, as massive particles can be born from the existing energy (the equivalence of mass and energy is proven in Albert Einstein's special theory of relativity, created in 1905). However, at low energies, W and Z particles (and hence weak interactions) occur rarely. Since physicists are limited to relatively low energies in earthly conditions, researchers began to notice differences between electromagnetic and weak interactions. In the Weinberg-Salam theory, the masses of W+, W–, and Z0 particles are not artificially introduced but arise naturally from the mechanism of spontaneous symmetry breaking. Estimates of the masses of these particles can be obtained from the theory itself. Each of the two W particles is about 80 times heavier than a proton, and the Z particle is even heavier.

Both Weinberg and Salam expected that with the help of the mathematical procedure known as renormalization, they would be able to obtain finite values for all measurable quantities. However, since neither Weinberg nor Salam were able to confirm their expectations with calculations, their theory received little attention until 1971. In 1971, Danish physicist Gerardus 't Hooft made significant progress in renormalization and, in collaboration with other theorists, completed the proof of this theory. Two years later, researchers from the Fermi National Accelerator Laboratory near Chicago and the European Organization for Nuclear Research (CERN) near Geneva discovered weak neutral currents, thereby confirming the theory proposed by Salam, Glashow, and Weinberg. In 1983, the W and Z particles themselves were discovered at CERN by Carlo Rubbia and his colleagues.

Later Career and Honors

In addition to his contributions to theoretical physics, Salam had a wide range of other interests. From 1955 to 1958, he worked as a scientific secretary at the United Nations for the Geneva Conference on the Peaceful Uses of Atomic Energy. From 1964 to 1975, he served as a member of the Advisory Committee on Science and Technology at the United Nations, and in 1971 and 1972, he was the chairman of this committee. In 1981, Salam served as the chairman of the Advisory Committee on Science, Technology, and Social Processes at UNESCO. He was also a member of various education and science committees in Pakistan and was appointed the chief scientific advisor to the President of Pakistan's office in 1961, a position he held until 1974. In addition to the Nobel Prize, Salam received numerous awards and honors, including the Maxwell Medal from the London Physical Society (1961), the Hughes Medal (1964), and the Royal Medal (1978) of the Royal Society. He was a member of the London Royal Society, the Swedish Royal Academy of Sciences, the Pontifical Academy of Sciences, and an honorary or foreign member of the American Academy of Arts and Sciences, the National Academy of Sciences, the USSR Academy of Sciences, and other scientific societies. Salam held nearly thirty honorary degrees, including those from Punjab, Edinburgh, Bristol, Cambridge, City College of the City University of New York, and the University of Glasgow.

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