Abdus Salam – Nobel Laureate in Physics

Submitted by Prof. Dr. Ibrahim B Syed

Summary:

Dr. Abdus Salam was one of the great physicists of the twentieth century. He made fundamental and far-reaching contributions to theoretical physics.In the previous century, James Clerk Maxwell brought about the first great unification in physics when he showed that the electric and magnetic forces are manifestations of a single force – the electromagnetic force, responsible for light. In 1968 Salam, Weinberg, and Glashow independently produced a second great unification, uniting the electromagnetic force with the weak nuclear force to produce the electroweak force.

Dr. Abdus Salam was a dedicated educationalist and a noble soul who served his country with an earnest zeal, promoting the education science and training a large number of first rank physicists.

Childhood

Abdus Salam was born in Jhang, a small town in what is now Pakistan, on January 29, 1926. His father was Chaudhry Muhammad Hussain, an education official in the Department of Education in a poor farming district, and his mother was Hajira Nabi Baksh. Abdus was the eldest of their eight children. His family has a long tradition of piety and learning.

Education

Abdus attended school in the town of Jhang. From an early age he showed enormous talent in mathematics and science. He also developed a lifelong love of poetry in English, Persian, and Punjabi. He cycled home from the school. At age 14, he amazed the people of Jhang when he achieved the highest marks ever seen in Punjab University’s entrance examination/ Matriculation Examination. Nearly the whole town turned out to celebrate his achievement. Not surprisingly, he was given a university scholarship. He graduated with a Master’s degree in Mathematics in 1946, age 20. [1]

Abdus Salam said: When I was at school in about 1936 I remember the teacher giving us a lecture on the basic forces in Nature. He began with gravity. Of course, we had all heard of gravity. Then he went on to say “Electricity. Now there is a force called electricity, but it doesn’t live in our town Jhang, it lives in the capital town of Lahore, 100 miles to the east”. He had just heard of the nuclear force and he said “that only exists in Europe”. This is to demonstrate what it was like to be taught in a developing country. [2]

In the same year (1946) he was awarded a three year scholarship to study for a Bachelor’s degree at St. John’s College, Cambridge, UK,. In 1949, after two years he graduated with first class honors in Mathematics. A year later, he graduated with first class honors in Physics.

In 1950 he received the Smith’s Prize from Cambridge University for the most outstanding pre-doctoral contribution to physics at the university. He also obtained a PhD in theoretical physics at Cambridge; his thesis, published in 1951, contained fundamental work in quantum electrodynamics which had already gained him an international reputation. [3]

His PhD Thesis was on “Developments in quantum theory of fields”. This was a rather brilliant work: in addition to making his name as a physicist, it resulted in him winning a share of the highly prestigious Adams Prize for mathematical sciences in 1956. To be eligible for the prize, candidates had to be under forty years of age and living in the UK. Previous winners included James Clerk Maxwell, J.J. Thomson and Subrahmanyan Chandrasekhar. [1]

Career

Pakistan and the UK
In 1951, age 25, Salam returned to the city of Lahore, in now independent Pakistan, to teach Mathematics at Government College, Lahore. He was filled with hope that he could inspire a new generation of young people to become scientists and modernize society. The following year(1952), he was appointed Head of Mathematics at Punjab University.

He had come back with the intention of founding a school of research, but it soon became clear that this was impossible. To pursue a career of research in theoretical physics he had no alternative at that time but to leave his own country and work abroad. This was motivated by another important event that took place in 1953, Lahore suffered riots in which a very large number of Ahmadis were murdered. Ahmadis consider themselves to be Muslim, but are seen as heretics by many other Muslims. Salam, who was an Ahmadi, decided to leave Pakistan and return to Cambridge.

Salam spent four years as a lecturer at Cambridge until, in 1957, age 31, he was appointed Professor of Theoretical Physics at Imperial College, London. Since 1964 has combined this position with that of Director of the ICTP(International Centre For Theoretical Physics )., Trieste, Italy. In 1959, he was elected a Fellow of the Royal Society. [1]

Many years later he succeeded in finding a way to solve the heartbreaking dilemma faced by many young and gifted theoretical physicists from developing countries. At the ICTP (International Center for Theoretical Physics), Trieste, Italy, which he created, he instituted the famous “Associateships” which allowed deserving young physicists to spend their vacations there in an invigorating atmosphere, in close touch with their peers in research and with the leaders in their own field, losing their sense of isolation and returning to their own country for nine months of the academic year refreshed and recharged.

In 1954 Salam left his native country for a lectureship at Cambridge, and since then has visited Pakistan as adviser on science policy. His work for Pakistan has, however, been far-reaching and influential. He was a member of the Pakistan Atomic Energy Commission, a member of the Scientific Commission of Pakistan and was Chief Scientific Adviser to the President from 1961 to 1974.

For more than forty years he has been a prolific researcher in theoretical elementary particle physics. He has either pioneered or been associated with all the important developments in this field, maintaining a constant and fertile flow of brilliant ideas. For thirty years he has used his academic reputation to add weight to his active and influential participation in international scientific affairs. He has served on a number of United Nations committees concerned with the advancement of science and technology in developing countries.

To accommodate the astonishing volume of activity that he undertakes, Professor Salam cuts out such inessentials as holidays, parties and entertainments. Faced with such an example, the staff of the Centre find it very difficult to complain that they are overworked.

He has a way of keeping his administrative staff at the ICTP fully alive to the real aim of the Centre – the fostering through training and research of the advancement of theoretical physics, with special regard to the needs of developing countries. Inspired by their personal regard for him and encouraged by the fact that he works harder than any of them, the staff cheerfully submit to working conditions that would be unthinkable at the (International Atomic Energy Agency in Vienna (IAEA). The money he received from the Atoms for Peace Medal and Award he spent on setting up a fund for young Pakistani physicists to visit the ICTP. He uses his share of the Nobel Prize entirely for the benefit of physicists from developing countries and does not spend a penny of it on himself or his family. [3]

Abdus Salam is known to be a devout Muslim, whose religion does not occupy a separate compartment of his life; it is inseparable from his work and family life. He once wrote: “The Holy Quran enjoins us to reflect on the verities of Allah’s created laws of nature; however, that our generation has been privileged to glimpse a part of His design is a bounty and a grace for which I render thanks with a humble heart.” [3]

Work

According to modern physics, four fundamental forces exist in nature. Electromagnetic interaction is one of these. The weak interaction – responsible, for example, for the beta decay of nuclei – is another. Thanks to contributions made by Abdus Salam, Sheldon Glashow,and Steven Weinberg in 1968, these two interactions were unified to one single, called electroweak. The theory predicted, for example, that weak interaction manifests itself in “neutral weak currents” when certain elementary particles interact. This was later confirmed. [4]

Fig.1. Left side: Abdus Salam. Right side: Decay scheme of a neutron. The W boson is an intermediate particle in beta decay. The neutron first decays into a W boson. [1]

In the previous century, James Clerk Maxwell brought about the first great unification in physics when he showed that the electric and magnetic forces are manifestations of a single force – the electromagnetic force, responsible for light.

In 1968 Salam, Weinberg, and Glashow independently produced a second great unification, uniting the electromagnetic force with the weak nuclear force to produce the electroweak force.

The Electroweak Force

The Initial Problem

At a physics conference in Seattle in 1956, Salam became very excited listening to Chen-Ning Yang, describe parity violation – Yang and his colleague Tsung-Dao Lee would be awarded the 1957 Nobel Prize in Physics for this work.

Yang described how parity, a property which physicists believed was always conserved – like energy, momentum, and electric charge – need not be conserved in weak nuclear interactions, such as beta decay.

The implication was that Nature could tell the difference between left and right. Why, Salam wondered, was left-right symmetry violated in weak interactions, but conserved in electromagnetic interactions? He convinced himself, correctly, that the answer lay in a gauge theory – the first of which had been Maxwell’s formulation of electrodynamics.

Predicting the W and Z Bosons

Salam worked on the problem with his PhD student Ronald Shaw and, in 196l-62, Steven Weinberg spent a year with Salam at Imperial College.

The scientists produced a theory saying that while the electromagnetic force was transmitted by massless photons, there must exist particles with mass involved in a unified force – the electroweak force. They theorized the existence of W and Z bosons.

W and Z bosons, they said, are the particles with mass that take part in beta decay of an atomic nucleus.

Fig. 2. A neutron undergoes beta decay. The neutron can be free or within a nucleus. The decay produces a proton, a high energy electron, and an electron antineutrino. [1]

The net outcome of beta decay is that a neutron turns into a beta particle (a high energy electron), a proton, and an electron antineutrino.

The W boson is an intermediate particle in beta decay. The neutron first decays into a W boson. In the case of beta decay, the W boson is negatively charged, written W^–. It hangs around for an incredibly short amount of time: 3 × 10^-25 seconds, before decaying into a proton, beta particle, and antineutrino.

Z bosons carry no electric charge, but carry momentum. They are observed in very high energy situations.

The fact that the force carriers of the electroweak force – the W and Z bosons – have mass while photons have no mass was a major problem, because in an SU(2) gauge theory (particle physics jargon for the gauge framework Salam and others were working within) bosons must have no mass.

Peter Higgs solved the problem of bosons with masses in 1964 with the Higgs mechanism, predicting the Higgs boson. (Higgs was awarded the 2013 Nobel Prize in Physics for his work.)

W and Z Bosons are Discovered

Z boson interactions, called weak neutral currents, because Z bosons carry no charge, were observed at CERN in 1973. W bosons were observed in 1983.

Taken together, the SU(2) gauge theory of the weak interaction, plus the electromagnetic interaction, plus the Higgs mechanism produces the Glashow-Weinberg-Salam model, finalized in 1968. The model successfully unified the electromagnetic and weak forces into the electroweak force.[1]

Nobel Prize

Glashow, Salam, and Weinberg shared the 1979 Nobel Prize in Physics: “for their contributions to the theory of the unified weak and electromagnetic interaction between elementary particles, including, inter alia, the prediction of the weak neutral current”. Prize share: 1/3

Affiliation at the time of the award: International Centre for Theoretical Physics, Trieste, Italy , Imperial College, London, United Kingdom. [1]

Scientific Achievements [1]

Salam’s best known contributions to science include:

two-component neutrino theory and the prediction of the inevitable parity violation in weak interactions
gauge unification of weak and electromagnetic interactions-the unified force is known as the “electroweak” force, named by Salam
predicted existence of weak neutral currents and W particles and Z particles before their experimental discovery
symmetry properties of elementary particles and unity symmetry
renormalization of meson theories
gravity theory and its role in particle physics including two tensor theory of gravity and strong interaction physics
supersymmetry theory including formulation of superspace and formalism of superfields

Personal Life

In 1949, age 23, Salam married his 22-year-old cousin Amtul Hafeez Hussain. The couple had three daughters and a son. In November 1967, Salam married the biophysicist Louise Johnson, with whom he had a son and a daughter. Amtul Hafeez Begum (m. 1949–1996) Louise Johnson (m. 1968–1996) He had a total of Children 6

In 1974, Salam was saddened when Pakistan’s government passed a law declaring Ahmadis to be non-Muslims. In 1980, after he received the Nobel Prize, he was invited as an honored guest to the Quaid-e-Azam University in Pakistan’s capital city, Islamabad. The ceremony was cancelled because extremists threatened to break Salam’s legs if he turned up at the university.[1]

Death

In the mid-1980s, Salam began suffering from a degenerative neurological disorder. Eventually he was confined to a wheelchair. He retired from his chair at Imperial College in 1994, age 68.

Abdus Salam died peacefully, age 70, at home in Oxford on November 21, 1996. He was buried four days later in the Ahmadi city of Rabwah, Pakistan.

Fig. 3.In 1998, Pakistan issued a stamp in honor of Salam. [1]

Other Work

During the early 1960s, Salam played significant roles in establishing the Pakistan Atomic Energy Commission (PAEC) and Pakistan’s Space and Upper Atmosphere Research Commission (SUPARCO).

Salam was passionate about promoting science in developing countries. He recalled there had once been a golden age of Islamic science, when for hundreds of years Islamic scientists had led the world. He urged Muslims to regain the spirit of free enquiry that existed in those times.

Salam was the founder of the Third World Academy of Sciences (TWAS) and the International Centre for Theoretical Physics (ICTP).

He donated all the money he received from his Nobel Prize to setting up a fund in Pakistan to promote educational opportunities. [1]

Awards [5]

In 1979, Salam was awarded the 1979 Nobel Prize in Physics, along with Glashow and Weinberg, For their contributions to the theory of the unified weak and electromagnetic interaction between elementary particles, including, inter alia, the prediction of the weak neutral current. Salam received high civil and science awards from all over the world. Salam is recipient of first high civil awards – Star of Pakistan (1959) and the Nishan-e-Imtiaz (1979) – awarded both by President of Pakistan for his outstanding services to Pakistan. The National Center for Physics (NCP) contains a Abdus Salam Museum dedicated to the life of Salam and his work as he discovered and formulated the Electroweak Theory. Below is the list of awards that were conferred to Salam in his lifetime.

Nobel Prize in Physics (Stockholm, Sweden) (1979)

Hopkins Prize (Cambridge University) for “the most outstanding contribution to Physics during 1957–1958”

Adams Prize (Cambridge University) (1958)

Fellow of the Royal Society (1959)

Smith’s Prize (Cambridge University) (1950)

Sitara-e-Pakistan for contribution to science in Pakistan (1959)

Pride of Performance Medal and Award (1959)

First recipient of Maxwell Medal and Award (Physical Society, London) (1961)

Hughes Medal (Royal Society, London) (1964)

Atoms for Peace Award (Atoms for Peace Foundation) (1968)

J. Robert Oppenheimer Memorial Prize and Medal (University of Miami) (1971)

Guthrie Medal and Prize (1976)

Sir DevaprasadSarvadhikary Gold Medal (Calcutta University) (1977)

Matteuci Medal (Accademia Nazionale deiLincei, Rome) (1978)

John Torrence Tate Medal (American Institute of Physics) (1978)

Royal Medal (Royal Society, London) (1978)

Nishan-e-Imtiaz for outstanding performance in Scientific projects in Pakistan (1979)

Einstein Medal (UNESCO, Paris) (1979)

Shri R.D. Birla Award (India Physics Association) (1979)

Order of Andres Bello (Venezuela) (1980)

Order of Istiqlal (Jordan) (1980)

Cavaliere de Gran Croce dell’Ordine al Meritodella Repubblica Italiana (1980)

Josef Stefan Medal (Josef Stefan Institute, Ljublijana) (1980)

Gold Medal for Outstanding Contributions to Physics (Czechoslovak Academy of Sciences, Prague) (1981)

Peace Medal (Charles University, Prague) (1981)

Lomonosov Gold Medal (USSR Academy of Sciences) (1983)

Premio Umberto Biancamano (Italy) (1986)

Dayemi International Peace Award (Bangladesh) (1986)

First Edinburgh Medal and Prize (Scotland) (1988)

“Genoa” International Development of Peoples Prize (Italy) (1988)

Honorary Knight Commander of the Order of the British Empire (1989)

Catalunya International Prize (Spain) (1990)

Copley Medal (Royal Society, London) (1990)

References