comment: Dr Salam’s legacy —Munir Attaullah
The achievement of Dr Salam and his colleagues was to reconcile these conflicting considerations using a concept called ‘gauge invariance’. Their prediction of the existence of these ‘massive’ bosons (the W and the Z), and their exact respective masses, was experimentally verified
I ended my column last week by introducing a phrase — ‘spontaneous symmetry breaking’ — and a reference to Professor Abdus Salam (who used that concept in his Nobel Prize-winning work). That concluding thought is my point of departure for today’s column. Why?
Well, even though I am no believer in the Jungian concept of ‘synchronicity’, consider the following set of curious converging facts: I was conscious as I wrote the previous column that it was being written in the week that Dr Salam died 12 year ago (on November 21, 1996); therefore, a follow-up column on the man himself suggested itself automatically, especially as it would naturally be related to the subject matter (symmetry) of my previous two columns.
Also, the 2008 Nobel Prize for Physics (to be formally awarded a week from now) is to be shared by three Japanese-born theoretical physicists for their work on the same subject. Professor Nambu is being honoured for “the discovery of the mechanism of spontaneous symmetry breaking in subatomic particles”; while Drs Kobayashi and Maskawa get the nod for “discovering the origin of the broken symmetry which predicts the existence of at least 3 families of quarks in nature”. (Quarks are the sub-constituents of protons — a composite particle that itself is part of the nucleus of an atom).
Finally, and most importantly, I happened to visit and browse the website www.abdussalamdocufilm.com, and I strongly urge readers to do the same. Two enterprising young Pakistani scientists, Omar Vandal and Zakir Thavir, are planning a documentary film on the life and work of Dr Salam. In my opinion, this ambitious project deserves all the financial support and publicity it can get. I certainly plan to contribute whatever my modest means will allow. The website will tell you what some reputable institutions, and better-known individuals than me, have to say in support of the project. Overseen by a distinguished international panel of advisors, the script is written by the famous science writer, Nigel Calder, and the award-winning Sabiha Sumar has been chosen as the director.
It is not my purpose here to describe the achievements of Dr Salam. In the Internet Age, that is easy enough for anyone to do on his own. But there is one aspect of his life I would like to highlight: his untiring, and eventually successful, efforts to establish the International Centre for Theoretical Physics (ICTP) in Trieste, of which he was selected as the founding director.
This centre of excellence was intended by him to help Third World physicists keep pace with the latest developments in their subject by interacting there with their peers from other parts of the world. To give you an idea of how successfully his vision has been implemented, consider the following statistics:
In 2007, some 7000 scientists from all over the world visited the centre, of whom some 50 percent came from the developed world, mostly at their own expense. The physicists who came from the developing world (and that included 72 Pakistanis, including 16 women) were helped financially to different extents.
But enough of these background justifications. Let me return to my main theme for today. So, what is ‘spontaneous symmetry breaking’; why is it an important concept in fundamental physics; and what was Prof Salam’s contribution that earned him a share of the Nobel Prize in 1979?
Unfortunately, none of the foregoing is easy to explain in simple layman terms. However, as I would consider not trying to do so a dereliction of duty, I will do the best I can, using the minimum amount of jargon.
Let us start with a broad picture of the universe, as we now know it. Leaving aside gravity (and the gravitational ‘force’), physicists explain everything else that happens in the universe in terms of two types of fundamental and indivisible families of sub-atomic particles: ‘fermions’ and ‘bosons’. Fermions are ‘matter’ particles, such as electrons and quarks (the sub-constituents of protons). Bosons (such as a ‘photon’ — the particle of light) are what are called ‘force’ particles, and there are (apart from the gravitational force) three known forces of Nature: the electro-magnetic force, and the strong and weak nuclear forces.
What is a ‘force’? It is no more than the external manifestation of types of fermions, exchanging (by absorbing and/or emitting) types of bosons between themselves. The transfer of energy and momentum in this process (physicists call it ‘interaction’) mimics a ‘force’. Thus the electro-magnetic force is a manifestation of electrons exchanging ‘photons’; the strong nuclear force is what binds the constituents of the atomic nucleus through the exchange of bosons called gluons; and the weak nuclear force (responsible for radioactivity) is the consequence of the exchange within the nucleus of bosons called W and Z.
A unique feature of the weak nuclear force was the experimentally known violation of certain universal symmetry laws (known as CPT — charge, parity, and time — invariance, or conservation) obeyed by the electromagnetic force. Why should this be so? Also, theory demanded (again on symmetry and invariance principles) that these force-carrying particles (bosons) should have zero mass, like the photon. But the most plausible theory for explaining the weak nuclear force postulated massively heavy (in relative terms, of course!) intermediate bosons that rapidly decayed into the actual particles observed in the experiments.
The achievement of Dr Salam and his colleagues was to reconcile these conflicting considerations using a concept called ‘gauge invariance’. Their prediction of the existence of these ‘massive’ bosons (the W and the Z), and their exact respective masses, was experimentally verified. And theory was vindicated by showing how the W and Z bosons acquired mass (through a ‘broken symmetry’, technically known as ‘the Higgs mechanism’, that threw the universe, as it expanded and cooled, into a slight imbalance some 14 billion years ago).
And what is ‘spontaneous symmetry breaking’?
Prof Nambu explains the concept in the following manner. Think of an invisible round table, set for dinner. Between the dinner plates is a napkin for each guest. As the guests sit down for dinner, should they pick up the napkin on the left or the right? The two situations are identical.
However, once the first guest sits down and breaks this symmetry by picking up the napkin on his right (or left) — possibly for no particular reason, hence ‘spontaneous’ — everyone else must do the same to maintain the symmetry. The point is that this ‘broken’ symmetry an observer witnesses (that of every guest picking up the napkin on his right) is indicative of a deeper underlying symmetry: that of the round table.
The writer is a businessman. A selection of his columns is now available in book form. Visit munirattaullah.com