Family of the Heart Seminar - September 10, 2004
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PROF. ABDUS SALAM'S CONTRIBUTIONS TO THE WORLD OF SCIENCE” |
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By Darakhshanda S., Toronto ON.
“Neutral current bring rewards” was the head line that appeared in the Nature magazine of 18thOctober,
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1979. The Press release from the Royal Swedish Academy of Sciences
on October15, 1979 read Nobel Prize in Physics to be shared equally between
Professor Sheldon L Glashow, Harvard University USA, Professor Abdus Salam ICTP,
Italy and Imperial College Great Britain, and Professor Steven Weinberg, Harvard
University, USA.
Today exactly after 25 years I take the pleasure to
talk about what was the Contribution of Abdus Salam to the World of Science and
what is it all about that brought honour to our country.
The focus of Abdus Salam’s research had been the
micro world of atom. The study of the subject dates back to centuries but the
mystery is yet not solved completely. Atom can be defined as the smallest
representative of an element that consists of the negatively charged electrons
revolving around a very dense nucleus composed of positively charged protons and
neutrons. Certain types of forces hold these building blocks of an atom
together. For example, the electromagnetic force carried by photons holds the
electrons and the nucleons together to form a neutral atom. This force
represents the interaction between charges. The electromagnetic force also holds
the atoms together to form the molecules and the aggregates of molecules. The
aggregates could be small or large even as large as you and I. The chemical and
biological molecules interact with each other due to the electromagnetic forces.
Essentially, we are electromagnetic creatures inhabiting an electromagnetic
planet.
Towards the end of the last century, certain heavy
elements were found to exhibit radioactivity. This discovery disclosed the
existence of strong and weak nuclear forces. As a consequence, Physics of atomic
nucleus was developed extensively. The strong nuclear force carried by gluons
holds the protons and neutrons of the nucleus together despite a similar charge
on them. The weak nuclear force is responsible for beta decay of the atomic
nuclei. The process involves decay of the neutron, with charge zero into a
positively charged proton, emission of negatively charged electron and a neutral
and massless neutrino. It is the weak force that mediates production of the
solar energy by converting hydrogen into deuterium. The micro world of atom is
thought to be governed by the weak, strong and electromagnetic forces, gravity
is a holdout. Indeed it is the interplay of the forces and the building blocks
that gives rise to enormous beauty and complexity of our universe. The
Physicists categorize the fundamental building blocks as matter particles or
fermions and the force particles or the bosons.
Salam’s hypothetical equation postulated a
relationship between the electromagnetic and the weak nuclear forces. More
elaborately, the theory proposed that the two forces are the manifestation of
the same underlying force, and he named it the electroweak force. In the process
of proving this unification, it turned out that the phenomenon was not only
factual but it also indicated the existence of certain particles that were not
known before. Hence the theory unraveled the then undiscovered particles, the
weak vector bosons, known as W and Z bosons. W-bosons mediate charge current
while Z-bosons mediate neutral current of the weak force.
The theme Salam worked on goes fairly back in the
past. From the earliest times in the history, man desired to understand the
complexities of nature in the fewest elementary concepts. The first pursuit has
been to discover wheels within wheels, to discover the innermost wheel if any
such existed. A second pursuit has been that for the fundamental forces,
which make the wheels, go round and enmesh with one another. The third
pursuit is for the unification of the forces into a single entity.
Newton in the seventeenth century, explained the two
disparate phenomena of falling an apple on the ground and moon revolving around
the earth by a common force, the gravity. In the nineteenth century, Oersted and
Faraday showed that electricity and magnetism represented different aspects of
the same force, electromagnetism. Then in 1865, Maxwell predicted the existence
of electromagnetic waves and interpreted light as electromagnetic wave event. In
fact, this discovery set a path for the entire electronic revolution of today
leading to the invention of radio, television and radar etc. X-rays discovered
as radiations of wavelength shorter than ultraviolet rays, were discovered by
the end of the nineteenth century and were immediately exploited in the medical
diagnostics.
Einstein who was born more than hundred years ago,
was the first to dream of the ultimate unification of all forces
(Electromagnetic force, strong nuclear force, weak nuclear force and gravity).
In 1905, Einstein showed the relationship between mass and energy through the
velocity of light thereby predicted that enormous amount of energy is bundled in
a few pounds of atoms. The world saw the evidence in 1945 in the destruction of
Hiroshima and Nagasaki.
While looking at a Scientist’s contributions, it is
very important to understand that no idea or discovery in Science can be
completely attributed to one person alone. Salam beautifully described this fact
in his Nobel lecture by quoting what G.P Thomson had said in his Nobel lecture
in 1937; “…The goddess of learning is fabled to have sprung full grown from
the brain of Zeus, but it is seldom that a scientific conception is born in its
final form or owns a single parent. More often it is a product of a series of
minds, each in turn modifying the ideas of those that came before and providing
material for those who come after.”
Salam, inspired by the discovery of unification of
electric and magnetic forces, Maxwell, and Einstein’s dream of uniting all the
forces into one, set out in pursuit of a common thread linking the
electromagnetic and the weak nuclear forces. The path he trod was not a bed of
roses.
An important thing to begin was the requirement of a
specific theoretical framework in which to fit in the idea of electroweak
synthesis. The gauge theory of mathematics that was developed by Yang and Mills
in the mid 1950s provided such a framework. Gauge theory was not new to Salam.
In fact, one of his students Ronald Shaw had independently employed the gauge
ideas of Maxwell with the internal symmetry of proton-neutron system in 1955.
However his Ph. D thesis work remained unpublished and thereby relatively
unknown.
Now the difficulty was that in order to be related,
the W boson (carrier of weak force) and photon (carrier of electromagnetic
force) must have had the same spin. Instead, the experimental data available in
1950s showed that W boson if existed at all exhibited no spin. Later it turned
out that the experiments had been conducted wrong. In September 1956, at the Seattle Conference, Salam heard
Yang and Lee, the Chinese American scientists. They proposed that weak nuclear
force violates the left-right symmetry. The proposal was alarmingly thought
provoking as the symmetry of the particles was a big hurdle in the theory of
electromagnetic-weak forces unification.
In the plane on his way back to London from America,
unable to sleep, he kept thinking of reason for the violation of symmetry in
weak interactions. During this thinking flashed back the question Rudolf Peierl
had asked him during his Ph. D examination. The question was, “because of
Maxwell’s principle of a gauge symmetry electromagnetism, photon is massless,
what is the reason that neutrino does not have a mass?” At that time no one
knew the answer to that question. Now during the long and restless journey over
the Atlantic Ocean, came the answer to Salam’s mind. The photon analogue for
the gauge symmetry was neutrino. That will explain as to why neutrino does not
have mass, it violates chiral symmetry and travels exactly with the velocity of
light. Next morning, very thrilled, Salam headed straight from the plane to the
Cavendish laboratory, worked out the necessary parameters and consequences of
the symmetry, rushed out and took a train to Birmingham where Peierls lived.
However, Peierl refused to accept Salam’s idea as an answer to his question.
He replied very kindly that he did not believe at all in the violation of
left-right symmetry in the case of weak nuclear forces. After this rejection,
Salam went straight to European Centre for Nuclear Research (CERN) in Geneva to
meet Pauli, the father of Neutrino. Pauli read Salam’s paper and returned it
back next morning with a message, “tell my friend Salam to think of something
better”. It must have been heart breaking indeed but Salam was not to give up.
The exceeding disappointment came to an end when a
few months later, Mrs. Wu’s, Lederman’s and Telegdi’s experiments provided
the experimental evidence of symmetry violation. Pauli wrote a fairly apologetic
letter to Salam in January, 1957. The idea of uniting the weak and the
electromagnetic force was developed one step further in late 1958. However, the
story does not go smooth from here either. More contradictions were ahead.
The next ideas Salam proposed faced vicious
contradiction from Pauli which was terrible and discouraging. Salam very
carefully put aside Pauli’s fierce and prejudiced attitude towards the
unification ideas, and concentrated on the points that were rightly raised.
These points were directed towards the problem of masses of the Yang and Mills
fields and that was a valid issue. The carrier of the strong electromagnetic
force, photon is massless, contrarily, the carrier of the weak force, W boson
was very heavy, about 100 times heavier than proton. Most of the physicists in
1950s including Wolfgang Pauli were not willing to accept the marriage of a very
heavy particle, W boson with the massless photon. Of course they were wrong. The
problem was solved seven years later with the understanding of Higgs mechanism.
In his Nobel lecture, Salam acknowledged Kibble at the Imperial College for
tutoring him the Higgs Mechanism.
In 1961 Goldstone showed that the spontaneous
breaking of the continuous internal symmetry paid its price in the appearance of
zero mass scalars-a. Salam and Weinberg at the Imperial College London, jointly
spent an year to prove this theorem. Eventually, in the years between 1961 and
1967, the phenomenon of symmetry breaking was comprehended. First, it was
realized that a pure electromagnetic current versus a pure neutral current
complemented each other and along with the gauge particles (W’, Z0
and g) a
theory of interaction was constructed that could explain parity violation for
weak and parity conservation for the electromagnetic phenomena. Salam and
Weinberg independently shaped up the electroweak theory and reported in their
elegant papers published in 1968 and 1967 respectively.
The next question was if the theory is renormalizable
or not and the proof came from t’Hooft’s work in 1971. As Coleman commented,
“t’Hooft’s work turned the Weinberg-Salam frog into an enchanted
prince”. The event was just preceded by the GIM (Glashow, Iliopoulos and
Maiani) mechanism (1970) emphasizing the existence of the fourth charmed quark
and its essential role in resolving the dilemma posed by the absence of
strangeness-breaking currents.
Now was the time for the crucial question of
experimental or quantitative verification of the theoretical idea as it is
utterly imperative in Physics. Salam recalled that on his way to Aix-en-Provence
for the 1973 European Conference, along with Paul Mathews, they decided to walk
from the train station to the resort where they were supposed to stay. Shortly
after, a car drove from behind and stopped. The driver, who happened to be
Musset glanced out of the window and asked if he was Salam. Upon affirmative
reply, he told Salam to get in the car as he had news for him. The thrilling
news was that they had found neutral currents at CERN. Salam, in describing his
feelings, quoted a mythical story about Einstein who was asked what he would
have thought if experiments had not confirmed his theory of light deflection.
Einstein is supposed to have said, “Madam, I would have thought the Lord has
missed a most marvelous opportunity”. Certainly, like Einstein Salam also
admitted that pure logical thinking has to be supplemented with the empirical
support as all knowledge of reality starts with experience and ends in it.
In his Nobel lecture, Salam also indicated that the
idea of electroweak unification was talked about as early as in 1937 by Kemmer
and in 1936 by Kemmer’s Ph. D supervisor Gregor Wentzel. In addition to these
names, Salam mentioned several others in his Nobel lecture in acknowledging
their rightful contributions to the electroweak theory. Even then he admitted of
inadvertently leaving some names that had in one way or the other contributed to
the theory.
Salam’s theory was now in full bloom. After having
passed all the tests, it had emerged as a Truth glowing and flawless. It brought
Nobility to its creator, a mysterious Man from the East and I am proud to say
from Pakistan. As an honour, Salam was awarded with a Doctorate of Science
degree from the Quid-e-Azam University, Islamabad, Pakistan. Also the Government
of Pakistan issued a postage stamp bearing the statement Abdus Salam, the
Scientist of Pakistan.
The particles, W and Z bosons predicted by the
electroweak theory were subsequently found at the superprotosynchroton facility
at CERN soon after. Carlo Rubbia and Simon Van der Meer from CERN, received
Nobel Prize of 1984 for the discovery of these particles. Since this discovery
confirmed the earlier prediction made by Salam, Weinberg and Glashow, they were
also invited to the 1984 Nobel Prize Ceremony.
The electroweak theory introduced a pattern for the
incorporation of all the ideas into what later became known as Standard Model.
In the “standard Model” of high energy Physics, Salam’s electroweak theory
occupies the core position. It seems the mission is accomplished, but no, wait a
minute, Salam was not to stop after the phenomenal victory of the electroweak
theory. Together with Jogesh Pati, a pal from India, he speculated unification
of the electroweak and strong nuclear forces, named it as Grand Unification. In
the context of this new idea, they predicted the proton decay. The theory
initiated by Salam remain to be further elaborated and proved.
In the concluding remarks of his Nobel Lecture, Salam expressed his continuous amazement over the depth nature revealed on every occasion it was explored. He also predicted that for the future Physics holds even more surprises, and that it will change even more radically than ever.
Since the theory explains fundamental subatomic
phenomena, its implications in the interactions of biological molecules are
going to be inevitable. In the due course of time when more of the missing links
are found, the theory may lead to the comprehension of many of the health
problems. The radioactive compounds due to their beta radiations are already
used in the diagnosis and treatment of cancer. The beta decay of heavy isotopes
of carbon into nitrogen is also utilized for dating of organic archeological
remains. It is very much likely that the knowledge will eventually be exploited
to change the future of medical diagnostics, treatment and/or agricultural
production. However, it is hard to predict how long it will take to discover and
develop a more revolutionary technology on the grounds of the basic phenomenon
the theory has revealed. Unfortunately, in addition to the beneficial uses, the
world has also seen the misuse of acquired nuclear physics knowledge and its
destructive effects. However, Salam had always emphasized for the use of nuclear
fision and fusion in the constructive pursposes, such as generation of power and
increase in the agricultural or food yield etc. As a Scientific secretary, Salam
contributed in the organization of two Geneva conferences on Peaceful Use of
Atomic Energy held in 1955 and 1958. Glashow envisioned that the electroweak
theory provided an amazing connection between physics, elementary particle
physics and astro-physics.
Salam believed in doing to the best of his abilities
without worrying of the ultimate results in the sense of materialistic
achievements. He never showed signs of despair for what could not be achieved.
His curious mind rejoiced the wonders of exploration, and he named his sense of
wonder as his inspiration. He seemed to agree with Eistein who believed that in
our materialistic ages only a deeply religious human being could be a serious
research scholar.
Walter Gilbert (Wally) remembered him with immense
regard as the mysterious man of East. Wally,
who became a renowned Professor of Theoretical Physics at Harvard University,
had completed his degree under the guidance of Abdus Salam. Wally was at
Cambridge when the double-stranded DNA molecule was discovered and he was a
close friend of James Watson. Perhaps, influenced by his friend Jim, Wally
switched to Biology. This very promising student received the Nobel Prize in
Chemistry for discovering the “repressor” just a year after Salam and made
his guru duly proud of him.
Salam’s profound interest in raising the level of
fundamental science in the developing countries led to the creation of
International Centre for Theoretical Physics (ICTP) in Trieste, Italy. For over
thirty years, Salam as a Director with full dedication kept the Centre afloat.
He raised finds on constant basis from Italian Government, from the City of
Trieste, from the UN, from the International Atomic Energy Agency in Vienna,
from a host of foundations and private benefactors. The Center provides the
scientists with opportunities to communicate with their peers from the developed
countries and encourages them to publish their work. In a period of over 30
years, the centre has hosted more than 60,000 scientists from 150 countries. The
center organized several meetings and welcomed the visitors in many areas of
science. Other than particle physicists, the visitors of ICTP belonged to the
areas of plasma physics, environmental analysis, chemistry and molecular
biology.
Another of Salam’s important contributions has been
the establishment of Third World Academy of Sciences (TWAS) in Trieste, Italy in
1985. The funds were again arranged from different sources including UN, Italian
Government and others. Its functions include short term scholarships to the
scientists from the developing countries for attending international seminars
and/or workshops related to their research. The Academy also provides funds for
basic research to the academic staff in the developing countries.
In Pakistan, Abdus Salam Award to the scientists for
the best performance was established in 1995. Science was his mission and he
spent every penny of the Nobel Prize he received for the betterment of Science
in his home country, Pakistan. The mysterious man from East stands above all the
praises that I can think of. His work speaks for him.
I would like to conclude my talk with an answer to
someone’s question,
Is Abdus Salam coming to the Seminar?
The answer is yes; he is very much with us today.
Great people never die.
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