EC George Sudarshan, the renowned theoretical physicist, is no more. The internet already echoes with accounts of his missed Nobel Prizes, and of his maintaining a strong connection with India in contrast to other expat luminaries. It is true that lesser men have won Nobel Prizes for smaller achievements. However, focusing on this aspect of his career misses the point. To physicists, his contributions speak for themselves — prize or no prize. This post tries to convey something of the physics, but also something first-hand about his long visits to India in the early '70s. While continuing as a distinguished faculty member at the University of Texas in Austin, he was also at the Centre for Theoretical Studies on the Indian Institute of Science campus for an extended period. The Centre was established by Prof Dhawan, then director of the IISc, quite openly as a place that would bring Prof Sudarshan, (often referred to as ECG) to India for a significant part of each year, and bring academic clout to this still somewhat sleepy campus.
This did have the desired result: young faculty in new areas — ecology, climate science, and of course ECG’s own area of high energy physics — were attracted, and came to stay and ultimately build their own active schools and departments. As a physics research student in Bengaluru at precisely that time, I was a major beneficiary of lectures by the new faculty, the international visitors who also came, and of course ECG himself — his door was open to young people. In those more leisurely times, long discussions were the norm; it was a chance to see this legend at close quarters.
My first impression was that he went out of his way not to conform to anyone’s prior concept of how a legendary physicist should behave. The strong accent of his native Kerala seemed completely unaffected by his long stay in the US. He showed up for one of his seminars in the traditional formal dress of that region. He moved in a wide circle, far beyond the usual academic ones — taking serious interest in yoga and meditation, for example. His touch when discussing physics was always light and made you see things in a different way, often provoking rather than answering the questioner. As one example, he was asked about “mass renormalisation”. This is a deep concept in quantum theory. Calculations of the behaviour of electrons were stuck in the 1940s until people realised that the infinite answers they were getting were because they were not using the physical value of the electron mass, which had changed because it was immersed in the electromagnetic field. But ECG was not going to rise to the bait and give a technical answer. He simply pointed us back to Archimedes who noted that his weight changed when he immersed himself in water!
While the content of his formal lectures was almost invariably mathematical, it was not presented very technically or formally. And it was never about 'this is what I did long ago and I am telling you about it' — the problem and the solution were served fresh. It was his current work in optics — even classical optics — which made the biggest impact on me simply because that was close to my own training and interest. It was a real education to hear about the new results coming out in his ongoing collaboration with Simon and Mukunda in the early 1980s, using the powerful tools of symmetry which were of course very much a part of the particle physicists' kit. It was only somewhat later that I got to better appreciate what he had done in the 1960s, both in particle physics and in quantum optics, by going back to the original papers and talking to experts. This delay was also because I never heard a talk by ECG on his past work, he was full of his current problem. It is not easy to convey what he did and why it is so important but here is my attempt.
After Marie Curie isolated and purified the highly radioactive element Radium, it was found that it could decay and emit particles in three different ways. The one that ECG worked on is called ‘beta decay’ or the ‘weak interaction’ in which an electron is emitted. This had been something of a mystery till two big steps were taken by two giants of early 20th century physics: Pauli proposed that along with the electron, another elusive particle — the neutrino — was emitted; and Fermi came up with a model in which a neutron could transform itself into a proton, an electron, and a neutrino (technically, antineutrino), all happening at a single point. This bold proposal immediately explained the broad features of beta decay of many elements — one universal fundamental process sufficed. But as experiments grew more accurate, it was clear that Fermi’s theory needed revision. The most striking experiment was by Chien-Shiung Wu, a (grievously under-recognised) woman physicist of Chinese origin in Columbia University and pioneer in this area of experiments. She found something never seen before, a violation of mirror symmetry. All other physical processes, when reflected in a mirror, continue to look like processes allowed by the laws of nature. But this was the first exception. This was so unexpected that Wu’s Columbia colleagues, Lee and Yang, won the Nobel Prize for taking the unthinkable step of giving up this symmetry and exploring the consequences — technically this is known as the discovery of parity violation.
In the aftermath of Lee and Yang’s proposal, weak interaction theory faced a crisis — there were now far too many candidates to replace Fermi’s simple proposal. Experiments showed conflicting results. It was in this chaos that a 26-year-old George Sudarshan went to his thesis supervisor Robert Marshak, with one possibility among the many. It is called V-A. Without saying what V and A are, one can characterise it as taking an even bolder step of saying that the (parity) violation is maximal. Remember, this was an outstanding problem on which all the famous physicists were working, and Sudarshan had to take a stand that some of the experiments were wrong. Marshak himself seems to have been somewhat tentative in presenting the work at a conference. Word of the new proposal reached the California Institute of Technology via Gell Mann, who talked to his colleague Feynman. They found another way of expressing the V-A proposal and carried it further. The later literature often refers to it as the Feynman Gell Mann theory, but the acknowledged fact is that they reformulated and exploited the concept which came from Sudarshan.
The second major contribution concerns an even older problem — the two-faced nature of light brought out by Planck and Einstein in the beginning of the 20th century. Wave or particle? One could see features of either, depending on the experiment. The basic theoretical tools needed to understand this were provided in 1928 by one more giant figure, Paul Dirac in Cambridge. But the tools had to be carefully applied in each particular case to understand each particular experiment. What was lacking was a general framework in which these two aspects were woven together. Such a framework was badly needed by the 1960s because lasers had been invented, and new experimental results were pouring in. The breakthrough uses a special kind of quantum state called a ‘coherent state’ as a building block. Non-technically, such a state is quantum but exhibits behaviour as close as possible to a classical wave. Roy Glauber of Harvard University published the first paper on this a few weeks earlier than Sudarshan’s independent work. But while Glauber’s was a first provisional step, it is clear that Sudarshan’s paper laid out the full picture pretty much in its final form. His frustration at the award of the Nobel Prize to Glauber is perhaps understandable.
There are many other elegant and innovative contributions that he made to many other areas of theoretical physics and each bears the stamp of his originality in formulating a problem and solving it. What we should all remember is that at least twice in his life, George Sudarshan saw further than all his contemporaries and pushed the frontier of what was known and understood. Of how many scientists can we say the same? And of them, how many come with such a unique life and personality?
Rajaram Nityananda teaches physics at the Azim Premji University. He has worked earlier with Raman Research Institute and Tata Institute of Fundamental Research.
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Updated Date: May 22, 2018 15:48:18 IST