SHORT FEATURE For the Pursuit of Excellence Dipayan Pal

Prof. Stephen William Hawking Prof. Amal Kumar Raychaudhuri (Source: IUCAA, Pune)

FTER the demise of fabled and widely celebrated The theory is believed to be the most successful theoretical physicist and cosmologist, Professor gravitational theory which Is universally accepted and well AStephen William Hawking on 14 March 2018, a sense adduced by observations. The first success of GTR was in of void-ness engulfed the academic as well as non-academic delineating the anomalous perihelion precession of Mercury. circles alike. But we are hardly aware of a home-grown scientist Since then, the theory has been used to define all manner of based in Calcutta who had a consequential impact on Hawking’s physical phenomena, including bending light, black holes and research work. the expanding universe. In 1915, Einstein startled the world through his enigmatic A Supernova Remnant (SNR) is a diffuse, expanding proposed theory ‘General ’ (GTR) that nebula resulting from a spectacular explosion of a star in transformed our understanding of the nature of space and which it ejects most of its mass in a violently expanding cloud time and it also transformed the understanding of classical of debris. If the remnant is massive enough (heavier than few physics from a new perspective. It is a geometrical theory solar masses), then the remnant itself squeezes inwards by of gravitation that generalises Sir Isaac Newton’s Law of gravity, forming a singularity, or (one of the ways universal gravitation and special relativity, providing a unified in which black hole forms). explanation of gravitation as a geometric property of space and In this regard, there is a relationship between the time or space-time (that gravitation is not caused due to force theoretical investigations of Stephen Hawking and Amal Kumar but rather manifestation of curved space and time), with this Raychaudhuri from Calcutta. Popularly known as AKR, he curvature being generated by the mass-energy and momentum was remarkable but a lesser-known physicist. Educated at of whatever matter and radiation present. Presidency College and , he subsequently

36 | Science Reporter | November 2018 In , the Raychaudhuri equation plays a significant role to explain the space-time singularities and gravitational focusing properties in cosmology. He aimed to address the fundamental question of singularity in the most simple and general form...

joined the Indian Association for the Cultivation of Science It is true that Hawking admired (IACS) as a Research Associate and then Ashutosh College, Calcutta, as a faculty member in 1950. Raychaudhuri’s contributions to In 1961, fortuitously he received an offer of a professorship Physics very much. His contributions at the Presidency College, the seat of academic excellence are widely recognised by the and his alma mater. While his work would change the dynamics of general relativity and cosmology, he spent most international scientific community. of his life doing monotonous lab work. In fact, it’s a miracle But AKR remains a hidden figure in to do such illustrious independent research work despite rigorous academic regulations of the university. His indelible his own homeland. contribution — pathbreaking equation (Raychaudhuri equation) — was discovered in 1954 under adverse and challenging There is such wide acceptability of this equation like circumstances and he obtained this feat by the sheer virtue of other notable equations in physics like ‘the Dirac equation self-learning. and Schroedinger equation’ that nobody cares about its origin Stephen Hawking’s doctoral thesis ‘Properties of or date of publication. The Raychaudhuri equation paved the expanding universes’ under the supervision of D.W. Sciama way for later research into the singularity problem. It would at the University of Cambridge begins with his work on the find its place in venerable textbooks on general relativity and ‘Hoyle-Narlikar theory of gravitation’, which was regarded as relativistic cosmology. The equation will stand firm so long an alternative to Einstein’s framework. In the second and last Einstein’s GTR stands. The equation remains a prime tool to chapters, he used Raychaudhuri’s findings while arriving at investigate the behaviour of black hole horizons. One would results on the existence of singularities in GR. Later research wonder if there is any research work of such grade to have works conducted based on his aforementioned thesis adduced emerged in post-independent . Raychaudhuri’s contributions extensively. AKR symbolised excellent scholarship and erudition. In general relativity, the Raychaudhuri equation plays His biography was authored by J.V. Narlikar and in 2005 a a significant role to explain the space-time singularities and documentary film had been produced on his life and work. gravitational focusing properties in cosmology. He aimed to His research work is as consequential as it could have got. We address the fundamental question of singularity in the most remember the monumental contributions of Stephen Hawking, simple and general form with no reference to any symmetry Jagdish Chandra Bose, Meghnad Saha, Satyendra Nath Bose, and any specific property of space-time and energy distribution. Subrahmanyan Chandrasekhar, C.V. Raman, etc. We also need The first mention of the term ‘Raychaudhuri Equation’ to remember his contributions. appeared in a research paper published in 1965 by George It is true that Hawking admired Raychaudhuri’s F.R. Ellis and Stephen Hawking. The Raychaudhuri equation contributions to Physics very much. His contributions are hit the zenith of fame as it was a key tool in the hands of widely recognised by the international scientific community. young relativists like Stephen Hawking and But AKR remains a hidden figure in his own homeland. in the middle of the late 1960s in their attempt to answer the question on the existence of space-time singularities and to Mr Dipayan Pal is an undergraduate student at Hans Raj College, explain the theory of universe. In fact, this equation is important University of Delhi and an independent researcher. He is also a Student as a fundamental lemma for the Penrose-Hawking singularity Fellow (elected) of Royal Anthropological Institute, UK. Address: C/o theorems. Pradip Kumar Pal, 96/4, K.G.R.S. Path, Bhadreswar, Hooghly, West -712124; Email: [email protected]

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