It’s Subrahmanyan Chandrasekhar’s birthday today. “Chandra”, as he was fondly known to friends and colleagues, was one of the twentieth century’s most important astrophysicists. In addition he was probably its most rigorous and mathematical, applying hard and baroque mathematics to problems ranging from hydrodynamics to collapsing stars. His Nobel Prize came in 1983, and it should have come earlier. Chandra’s life provides a good example of quiet rebellion against a traditional scientific establishment, and it’s for this reason that it deserves wide study.
By all accounts Chandra was marked to be a great scientist from his birth. Born in the city of Lahore (now in Pakistan) to a respected civil servant, he quickly outpaced his fellow students in his study of advanced mathematics and physics. In the 1920s when he was attending college in the progressive city of Madras (now Chennai) he met the renowned physicist Arnold Sommerfeld when Sommerfeld was visiting Madras, and was both shocked and fascinated to hear Sommerfeld tell him that quantum theory had rendered outdated much of the physics he had learnt. That however was a deficiency that Chandra could remedy. As the famous story goes, at the mere age of nineteen, on a long voyage from India to England to attend graduate school at the University of Cambridge, he did the calculation that was to enshrine his name in history. That analysis which used tools from relativity and quantum theory that were far beyond the grasp of any other nineteen year old physics student, finally led to the establishment of the so-called ‘Chandrasekhar limit‘, a limit for the mass a white dwarf can sustain before it collapses under the weight of its own gravity.
A few years later Chandra had a famous showdown with Arthur Eddington, the doyen of English astronomers and one of the most famous scientists in the world. It was Eddington who had confirmed Einstein’s famous prediction of starlight bending in 1919, and by 1935 when he went up against Chandrasekhar, he was renowned for both his physical theories and his popular writing. The showdown came in a seminar when Chandra put forward his carefully calculated contention that white dwarfs cannot be stable beyond a certain mass. What happened beyond that mass even Chandra did not know, but like his brilliant contemporary and friend Paul Dirac, he was brave enough to trust the mathematics. Eddington however saw Chandra’s theorizing leading to a pathological physical reality. He could not conceive of a star keeping on collapsing, and he simply stated without proof that there must be some law of nature that prevented this. It was the classic case of the bastion of conservatism going up against the brash new kid on the block, although Chandra was no brash Richard Feynman cheekily rocking the establishment: he was simply courageous enough to quietly follow the numbers wherever they led.
Characteristically, Chandra did not contradict Eddington any further. He realized that he was the underdog and wisely conceded defeat…for the moment. He then waited a full five decades before a host of other brilliant theoreticians and experimentalists validated his seminal insight. It was Chandra’s discovery of limiting masses for stars that finally led Robert Oppenheimer in 1939 to postulate the existence of black holes. In twentieth century physics, Oppenheimer and Chandra’s papers on gravitational collapse bracket two very different personalities. Chandra waited quietly after his confrontation with Eddington, while Oppenheimer curiously simply forgot about his own groundbreaking contribution and remained indifferent to it for the rest of his life. After the war, John Wheeler, Dennis Sciama and Yakov Zeldovich put the theory of black holes on a firm footing. Their students Stephen Hawking, Roger Penrose, Kip Thorne and others blazed new pathways that continue to spawn deep insights. But it all started with Chandra.
Chandra who had spent the 1930s in England finally emigrated to the United States in the 1940s, accepting an invitation at the Yerkes Observatory of the University of Chicago. He made this country his own, and like his fellow immigrants Hans Bethe and Enrico Fermi, did much to raise its standing in the world of science. His father who expected him to return to India was deeply pained, but Chandra was convinced that he could have a better life in America, one unfettered by hero worship and the trappings of fame and enriched by friends and freedom to pursue his ideas and opinions. Chandra’s invaluable knowledge of hydrodynamics could have been important on the Manhattan Project at Los Alamos. Oppenheimer did invite him, but the delay in his security clearance which probably resulted from a mix of bureaucracy and naive racism kept him from making what would undoubtedly have been key contributions to the complex problems of implosion. Instead of Los Alamos, Chandra spent the war years at the Aberdeen Proving Ground working on ballistics and trajectories.
At Yerkes and Chicago Chandra became famous for being a formidable teacher and top-notch researcher. He became friends with most of the leading physicists of the time, and wrote papers with his fellow Chicago physicist Enrico Fermi. Carl Sagan said that he learnt what mathematical elegance was from Chandra when he was a student there. The future Nobel Laureates C D Yang and T D Lee were taught by Chandra; he considered them so promising that he thought nothing of driving two hours to teach a class of two. In addition Chandra took the previously neglected ‘Astrophysical Journal’ to new heights. By all accounts he was a strict and fair editor; there are stories of him rejecting phone calls if they cam a minute after the official working hours of the journal.
Chandra’s mastery of astrophysics was total and incredibly diverse, and the sheer range of his understanding was probably unmatched by any other scientist from the field. His style was unique. Every decade he used to research an important topic. After spending ten fruitful years exploring it and making important contributions, he would then write an exhaustive treatise that would serve as the standard reference on the subject. He would then move on and conquer another realm for another decade. In this way Chandra mastered and explained stellar structure, radiative transfer, hydrodynamic and hydromagnetic stability, gravitational waves and black holes. Each one of these topics would have been enough to keep a physicist busy for his or her career.
His last great technical treatise was titled “The Mathematical Theory of Black Holes“. The volume is so densely mathematical that according to Chandra’s own admission, he had to literally invent new symbols when he ran out of the common mathematical, Greek and Latin ones. After putting the finishing touches on this formidable tome, Chandra perhaps wisely decided to spend the rest of his years on more popular topics. Even when exploring these his characteristic rigor and exhaustive approach were apparent. His last book was a detailed and yet accessible analysis of all of Newton’s theorems in his great “Principia”. After examining his own modern and Newton’s supposedly archaic approaches, Chandra concluded that Newton’s were still better.
As rigorous and hard an astrophysicist as he was, Chandra was also remarkably well read and cultured. His remarkable wife Lalitha kept him grounded and optimistic. His knowledge of music, art and literature was extensive and this immersion contributed to the memorable clarity of his lectures. He compiled his views on an integrated approach to science, art and the humanities in a set of lectures titled “Truth and Beauty: Aesthetics and Motivations in Science” which is well worth reading. It would not be an exaggeration that Chandra embodied both qualities in his more than six decades of amazing contributions to science. As only one tribute to him, NASA’s flagship x-ray observatory which is allowing us to probe hidden features of the cosmos is named Chandra.
Chandrasekhar remains a study in rigor and fortitude. In these troubled times, it’s also worth noting that he was one of those immigrants who made the United States great. When he and his wife Lalitha became American citizens in 1953 – much to the chagrin of his father and family in India who still expected them to return – Lalitha responded to his father with a sobering letter in which she extolled the democratic tradition in the US and Chandra’s and her growing fondness for what made the country unique. In a paragraph that is perhaps relevant to this year’s election, Lalitha said that she did not think it was right to sit by idly by doing nothing while the pall of McCarthyism descended on the country; she felt that she and Chandra had to participate in the country’s democratic process, and they could only do this by becoming citizens.
One can only hope that this country absorbs more intellects like Chandra and his wife and proudly proclaims them as its own.