Ashoke Sen: The Super String Man And The Mysteries Of The Universe
If there is a man in this country who stands a fair chance of winning the Nobel Prize in this decade, in physics for those who are curious, it is Ashoke Sen, says Rohit Gupta
There is a theory which states that if ever anybody discovers exactly what the universe is for and why it is here, it will instantly disappear and be replaced by something even more bizarre and inexplicable. There is another theory which states that this has already happened.
-The Hitchhiker’s Guide to the Galaxy, Douglas Adams
On the southern tip of Mumbai, standing on a rock that looks over the Arabian Sea, a man fidgets in the gentle breeze. He is not comfortable posing for photographs, shy of our shutterbug Ashima, and wholly wishing that he were somewhere else. Preferably the lab in Harish Chandra Institute, Allahabad. His eyes are refracted into huge globules by his thick glasses, as if they were octopuses in a clear pool. But why are we talking about a nerdy man sniffing coral, ladies and gentlemen? Why not some lady-killer, dot-com millionaire, match-fixer, or the new kid on the writer’s bandwagon.
In my opinion, if there is a man in this country who stands a fair chance of winning the Nobel Prize in this decade, in physics for those who are curious, it is Ashoke Sen, this forty-five year old string-theorist. If string theory were experimentally verifiable, it might have happened by now.
A string-theorist does not conjure karmic ways of alternative healing with nylon strings, nor does he perform the rope-trick, or play some nifty riffs on a stratocaster. Pardon the hyperbole, but his job is to unravel the knots that veil the secrets of this bottomless universe, peeling of skin after skin of this arrogant onion. He tries to tie the loose ends of an esoteric theory that just might be able to explain whether the chicken wanted to cross the road at all. String theory proposes to do so not by any brute philosophy, but by revealing to us how the fabric of space time is woven. It is the dawn of a new physics, the ambition of which is nothing less than the ultimate theory of everything. In contrast to the ambition of what he does, Ashoke Sen is humility personified.
In the tea-break at the Strings 2001conference, the photoflashes on Stephen Hawking are almost blinding. If amyotrophic lateral sclerosis does not take him, suffocation by reporters will. In the distance, behind a clump of fallen trees, Ashoke is safe in his anonymity. He has a whiteboard, a good problem in his head, and he’s busy solving it. The media never talked about him, but he is the sort of physicist that physicists talk about. We all know that physicists talk in Greek.
Independence in 1947 was especially traumatic for Calcutta. Religious tension had escalated with migration from the recently-formed East Pakistan, a large portion of the jute hinterland passed on as foreign land. In spite of this the infrastructure kept Calcutta the city to be in until the late fifties. Delhi had long replaced it as the political capital, and now Mumbai began replacing it as the economic capital of India. Summing up this decline was the Freight Equalization Policy of 1956 which equalized prices of “essential” items like steel and coal nationwide, while prices of private-sector produced items (like textiles) were not controlled. The eastern region was hardest hit. Ashoke was born in such an era of social upheaval, to the family of a physics teacher.
Ashoke does not know what took him to physics, but he remembers his cousin who was ten years older, who brought him a lot of pop-science books to read. He mulled over George Gamow’s One two three… infinity, and Bertrand Russell’s The ABC of Relativity at an early age. His Bachelor’s in Science from Presidency College (1972-75) only fed the curiosity brewing in his mind. As India won the match but lost the series to West Indies, and Salt Lake came into being as the opulent patch on a torn city, the educational system remained lax. Extended holidays and delayed scores gave Ashoke the chance to study basic quantum mechanics and tensor analysis, tools that would soon come in handy.
But how did a man born in such an economy and political chaos take up physics? Why does anybody? Sergey Cherkis, a string theorist himself, tells us about Russia, another communist regime at that time. In the backwoods’ villages in Russia, one can find houses with barely enough to eat, but always a copy or two of Life and Chemistry, and another science journal. When asked why this happened, he chuckled, “…because they cannot afford Playboy.”
The Stage of Science
It was known that there were only four basic forces in the universe: gravity, the electromagnetic force, and the weak nuclear and strong forces within atoms. The microcosm had been understood to a great extent, but nobody knew why gravity should exist. There was no evidence of any fundamental force particles for gravity and Newton’s law of gravity was working just fine. Einstein had proved the constancy of light, and that gravity is the warping of space-time by massive objects, not its result. This was the first time gravity had been explained, but not by quantum theory.
Scientists had also proved that heat is not an independent force, nor light: rather, they are just manifestations of electromagnetism. Some had begun to seek a unification deeper than that, to try and express the four basic forces in terms of only one force. They succeeded in unifying three to some extent, but gravity remained the odd one out.
Quantum physics (of the small, the uncertainty) and Einstein’s relativity (of space-time and large distances) were at loggerheads when any compatibility was attempted. The same science which explained the motions of the planets, could not explain the electrons around the nucleus. Einstein’s Dream of unification caused many a nightmare, and remained a dream.
Veneziano at CERN laboratories had noted in 1968 that the strong force could be expressed as a mathematical result if elementary particles were seen as tiny strings, instead of the point-like particles that we are used to. This idea was picked up by John Schwarz and Scherk and they started toying with strings, and were joined by Michael Green.
Ashoke does not know what took him to physics, but he remembers his cousin who was ten years older, who brought him a lot of pop-science books to read. He mulled over George Gamow’s One two three… Infinity, and Bertrand Russell’s The ABC of Relativity at an early age.
The Rising Sen
By this time Ashoke had finished his MSc at IIT Kanpur, and decided to take a PhD in physics from Stony Brook, New York. The years at Stony Brook shaped the man we see today. His neighbour at Stony Brook, and now a professor at TIFR
(Mumbai)—Sunil Mukhi remembers a day when he slept, very tired from the strenuous workload. When he woke up he found Ashoke at the doorstep, waiting with a cup of hot coffee for him. “He loved his friends, and also to go out for long walks alone. In fact, on a couple of occasions he was questioned by the police, who wanted to know why he was wandering around at strange hours.”
After Stony Brook, Ashoke moved on to Fermilab (Batavia, Illinois) and in 1984, he already had some familiarity with string theory concepts. In a bombshell paper, Schwarz and Green sparked the first revolution that proved the internal consistency of all string theories. Ashoke, a silent learner and observer till now, and barely thirty, was ready with his first big paper to ricochet that.
In a follow-up to the Schwarz-Green paper, he showed how it automatically leads to Einstein’s equations in general relativity. This only added to the rising frenzy in the physics community. After working on some more esoteric concepts, Ashoke turned his attention to the most outlandish concept of duality.
“According to this idea the same physical world may be described by apparently different theories. A particle which may look elementary in one theory may appear to be composite (made of two or more particles) in the other theory, although all the physical properties of the particle are identical in both theories. Such pairs of theories are known to be dual to each other. If this idea is correct, it will mean that there is no absolute distinction between elementary and composite particles, since whether a given particle is elementary or composite may depend on the particular version of the theory that we use to describe the system,” he explains. “The idea of duality was attractive, but had few supporters, since it was extremely difficult to prove or even test this idea by doing any concrete calculation. In one paper in 1994, I showed how one can test this idea by doing a concrete calculation, and using this method I found strong evidence for duality in one particular quantum field theory.”
At this point Ashoke conveniently understates the importance of this paper. Edward Witten, torch-bearer of string theory, used this very hypothesis to formulate his legendary 1995 paper, unifying all string-theories using dualities. Stephen Hawking, it must be noted at this point, is entirely uncomfortable with this use of dualities. In the same year, Sen released a paper explaining black-holes through string theory. This must have been an interesting read for Stephen Hawking, who was the foremost researcher in the field of black-holes at that time.
Sunil Mukhi adds, “Ashoke’s work on duality in 1994, at a time when this concept was not a mainstream one in string theory, was a major factor in the revolution that took place during that year. Witten described Ashoke’s work as the “last straw” that convinced him this was the right direction to pursue. Ashoke’s work not only had an impact on the physics of string theory, but it greatly impressed British mathematicians and led to Ashoke’s becoming a Fellow of The Royal Society at a very young age.” The calculation totally converted the string community. “Witten (often called The Pope) went from telling everyone this was a waste of time to telling them this was the most important thing to work on,” says Jeff Harvey.
The Genius and His P-branes
“In string theory, various extended dynamical objects are studied besides strings themselves. Membranes are one example. Ashoke pioneered the study of the decay of such “branes” in string theory, and conjectured a beautiful equation that describes the energetics of this process. Theoretical tests of his equation have confirmed that it is indeed correct. A good part of Strings 2001, the recent conference at TIFR, was focussed on Sen’s equation and its consequences,” explains Sunil Mukhi. He is down with the flu, but anxious to talk about his friend who he says is the “most purposeful man he has ever known”.
“Take Feynman—what do you care what other people think? And add to that an unshakeable sense of purpose. That’s Ashoke Sen for you.”
Ashoke loves a good dose of science fiction. He still reads Arthur C. Clarke and Isaac Asimov. He loves the Foundation trilogy by Asimov. While his kurta and oily-hair thrown back are reminiscent of Calcutta, Ashoke Sen could have easily passed off as a rustic poet, if you go by his looks. He clutches his bag very tightly, and speaks with a smile that does not fade when the sentence is over. Above his spectacles his forehead extends for miles, encasing a formidable engine of a brain.
It is this brain that can peer into the eleven dimensions that string theory predicts, contrary to the popular four. Six of these are supposedly curled up too small to be seen. String theory has gone beyond strings to include d-branes and p-branes and is now taking shape in the M-theory. M?—Mystery, Mother… call it what you will. When it actually succeeds and shows us the final picture, it may not be as we know it today. It may be some other people who finally put it together, but Ashoke Sen will remain as one of the grand architects.
This article was first published in the February 2001 issue
Photographed by Ashima Narain