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Adding basic entry and citations.

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{{short description|Indian physicist and polymath (1894–1974)}}
{{Use dmy dates|date=March 2025}}
{{Use Indian English|date=March 2025}}
{{Infobox scientist
| name = Nikhil Ranjan Sen
| honorific_suffix =
| image = M N Saha, J C Bose, J C Ghosh, Snehamoy Dutt, S N Bose, D M Bose, N R Sen, J N Mukherjee, N C Nag.jpg
| caption = Nikhil Ranjan Sen (standing, fourth from left) of Calcutta University with other scientists.
|birth_name =
| birth_date = {{birth date|1894|5|23|df=y}}
| birth_place = [[Dhaka]], [[Bengal Presidency]], [[British India]]
| death_date = {{death date and age|1963|1|13|1894|5|23|df=y}}
| death_place = [[Calcutta]], [[India]]
| alma_mater =[[Presidency College, Kolkata|Presidency College]] <br /> [[University of Calcutta]] <br /> [[Humboldt University, Berlin|University of Berlin]]
| academic_advisors = [[Max von Laue]]
| doctoral_students =
| notable_students =
| known_for =
| awards =
| spouse =
| field = [[Applied Mathematics]] <br /> [[Theory of Relativity]]
| work_institution = [[University of Calcutta]]
| signature =
}}
'''Nikhil Ranjan Sen''' (23 May 1894 – 13 January 1963) was an Indian-Bengali scientist who was a pioneer in the field of [[general relativity]] and called the father of applied mathematics in India. He received his PhD from [[Humboldt University of Berlin]] under the supervision of [[Max von Laue]], thus becoming the first Indian to get a doctorate in relativity. Sen also worked on [[cosmogony]], [[fluid dynamics]], [[potential theory]] and probability, and founded the first fluid dynamics laboratory in India.<ref name ="lifeandscience">{{ cite web | title = PDF Book Title- N R Sen - Life and Science | url = https://www.researchgate.net/publication/349769889|access-date=2023-06-26}}</ref> He pioneered the study of ballistics and missiles in India and was also an advocate for science education in the Bengali language. His Bengali-language book titled "Soura Jagat" (The Solar System) was published by Visva-Bharati in 1949.<ref>{{Cite web |url=https://www.ias.ac.in/article/fulltext/reso/020/07/0575-0604 |title=Asutosh Mukhopadhyay and his Mathematical Legacy |access-date=2023-06-26}}</ref>
<ref name="thewire">{{Cite web |url=https://science.thewire.in/the-sciences/remembering-nr-sen-a-less-known-student-of-the-calcutta-school-of-science/ |title=Remembering N.R.Sen, a Less Known Student of the Calcutta School of Science |date=2021-07-03 |access-date=2023-06-26}}</ref>
<ref name="Parliament ">Edited by Subodh Sengupta and Anjali Bose, "Sansad Bengali Charitavidhan", Volume I, Sahitya Sangsad, Kolkata, August 2016, p. 355, {{ISBN|978-81-7955-135-6}}</ref><ref name="INSA">{{Cite book |url=https://books.google.com/books?id=_l6eBQAAQBAJ&dq=nikhil+ranjan+sen+max+von+laue&pg=PT97 |title=The Scientific Edge - The Indian Scientist from Vedic to Modern Times |isbn=978-93-5118-928-2 |access-date=2023-06-26 |last1=Narlikar |first1=Jayant V. |date=4 August 2003 |publisher=Penguin UK }}</ref>

==Early life and education==

Nikhil Ranjan Sen was born on 23 May 1894 in [[Dacca|Dhaka]], the youngest of their four sons and four daughters of Kalimohan Sen and his wife Vidhumukhi Devi.<ref name ="lifeandscience" /> He attended Dhaka Collegiate School, where his classmate was the scientist [[Meghnad Saha]]. He then went to complete his school education at Rajshahi Collegiate School. In 1909, he obtained a scholarship with his third position in order of merit for the entrance examination of Calcutta University. After passing the intermediate examination in 1911, he studied honors mathematics in [[Presidency University, Kolkata|Presidency College]] in Calcutta, where he had Saha and [[Satyendranath Bose]] as classmates.<ref name="turbulence">{{Cite web |url=https://www.researchgate.net/publication/348244264|title=NR Sen and his Contribution to Turbulence Research|access-date=2023-06-26}}</ref> Bose, Saha, and Sen got the three highest spots in the 1913 honors examination in Calcutta University. They went on to become postgraduate students in Presidency College. Sen topped the 1916 Mixed Mathematics examination, a year after Bose and Saha topped the same exam.<ref name="Parliament" />

==Career and research==

Sen, Saha, and Bose joined the postgraduate department of mathematics in [[University of Calcutta]] at almost the same time in 1917. During this period, his papers on Newtonian potential, solid geometry, elasticity, and hydrodynamics were published in ''[[Philosophical Magazine]]'' and in the ''[[Bulletin of Calcutta Mathematical Society]]''.<ref name="appliedmaths">{{Cite book |url=https://books.google.com/books?id=45fDCgAAQBAJ&dq=nikhil+ranjan+sen+max+von+laue&pg=PR18|access-date=2023-06-26|title=Applied Mathematics - Kolkata, India, February 2014|isbn=978-81-322-2547-8 |last1=Sarkar |first1=Susmita |last2=Basu |first2=Uma |last3=De |first3=Soumen |date=13 October 2015 |publisher=Springer }}</ref>

In 1921, his thesis "Potentials of Uniform" was approved by G.T. Walker, D.N. Mallik, and [[Asutosh Mukherjee]] to be worthy of being awarded the doctorate (D.Sc.) degre from the university.<ref name="formative">{{Cite web |url=https://www.researchgate.net/publication/351368223
|access-date=2023-06-26|title=Nikhil Ranjan Sen - The Formative Years}}</ref> With an extra allowance of five hundred taka per month, he went to Germany for research work at the universities of Berlin, Munich, and Paris.<ref name="thewire" /> His work with Professor [[Arnold Sommerfeld]] in Munich from 1921 to 1922 was published in the [[Physikalische Zeitschrift]]. In the summer of 1922, he went to Berlin and studied under [[Max von Laue]] in the newly established Institute for Physics.<ref name="notable">{{Cite book |url=https://books.google.com/books?id=DfaVEAAAQBAJ&dq=Notable+Modern+Indian+Mathematicians+and+Statisticians+Chapter+Nikhil+Ranjan+Sen+%281894%E2%80%931963%29+Purabi+Mukherji&pg=PA73
|access-date=2023-06-26|title=Notable Modern Indian Mathematicians and Statisticians Chapter Nikhil Ranjan Sen (1894-1963)|isbn=978-981-19-6132-8 |last1=Mukherji |first1=Purabi |date=11 October 2022 |publisher=Springer }}</ref> Under von Laue, Sen received a Ph.D. from the [[Humboldt University, Berlin|University of Berlin]] for a general relativity dissertation on the boundary conditions for the gravitational field equations on surfaces of discontinuity.<ref name ="lifeandscience" /> In his dissertation, Sen found that Einstein's equations imply that gravitational forces hold together the parts of a particle, then he calculated the equilibrium of a charged particle with a definite spherical boundary. Sen also worked with von Laue on de Sitter universe and changes in potential of ions and emitted electrons of glowing metals during his stint in Germany.<ref name="formative" />

After returning home in 1924, he was appointed as "Rasbihari Ghosh Professor" in the newly formed Department of Applied Mathematics of Calcutta University. With Sen conducting and supervising research in areas related to the theory of relativity, he was considered the founder of the Calcutta School of Relativity in the 1930s. The Calcutta school investigated the effect of mass, density, radius, temperature and pressure in the stellar bodies. Sen refined models of the universe based on the General Theory of Relativity yet he was critical of Eddington and Milne's models.

In the early 1930s, Sen worked a considerable amount on wave mechanics and Dirac’ relativistic equations. He did some notable work on spherical harmonics and studied the relativistic effects in stellar bodies. Sen was a founding fellow of the [[Indian National Science Academy]] and Indian Science News Association in 1935.<ref name="INSA" /> He was also a founding member of the [[Indian Statistical Institute]] (ISI) Council and founding fellow of the National Institute of Sciences of India. In 1936, he established the Computational Laboratory and Fluid Dynamics Laboratory in his department in Calcutta University, the first fluid dynamics laboratory in India. Sen started working on the internal constitution of stars around 1940, after [[Hans Bethe]] established the law of energy generation.<ref name="turbulence" />

After the [[partition of India]], he included ballistics in the curriculum as he believed that it is an important science for the national defense of newly free India.<ref name="Parliament" />

In 1951, he was appointed Rippon Professor of the [[Indian Association for the Cultivation of Science]] and delivered three lectures on "The modern theory of turbulence".<ref name="turbulence" /> He proved the correctness and importance of the theories on turbulence of [[Heisenberg]], [[Subrahmanyan Chandrasekhar|Chandrasekhar]], [[Theodore von Karmen|von Karmen]] and others.<ref name="Parliament "/>

He collaborated with his students to construct stellar models based on the theoretical laws of thermonuclear energy. In 1954, Sen and T.C. Roy gave a singularity-free analytical method that strictly satisfied all the necessary conditions and could be fitted to the field of expanding universe. Their method correctly gave Newtonian approximations without using Einstein's subsidiary equations. He retired in 1959.<ref name="turbulence" />

==Science education in mother tongue==

When the Calcutta University Commission was formed in 1917 for the improvement of the education system, he pushed for a system of teaching science subjects under the liberal education system. Similar to Satyendranath Bose, he pushed the University Commission for science education in the Bengali language. His book titled "Soura Jagat" (The Solar System) in Bengali was published by Visva-Bharati in 1949.<ref name ="lifeandscience" />

==Honorary titles==
* 1934 - Member of "Earthquake Research Commission of India".
* 1935 - Fellow of Indian National Science Academy and Indian Science News Association
* 1935 - 1941 Member of the Council of the Indian National Science Academy
* 1936 - President of the Mathematics Department of the Indian Science Congress Organisation
* 1940 - 1941 Member of the Sectional Committee on Mathematics and Statistics of the Indian Science Congress Organisation
* 1949 - 1951 Council Member, Indian National Academy of Sciences
* 1951 - Ripon Professor, Indian Association for the Cultivation of Science, Calcutta
* 1952 - 1953 Indian Association for the Cultivation of [[Science Council]] Member of the Indian Association for the Cultivation of Science
* 1959-1960 Indian National Science Academy, vice-president.<ref name ="lifeandscience" />

==References==
{{reflist}}

==External links==
* https://www.caluniv.ac.in/academic/Apl-Math.html
* [https://epjh.epj.org/articles/epjh/abs/2021/01/13129_2021_Article_3/13129_2021_Article_3.html N.R. Sen: Father of Indian Applied mathematics]

{{Authority control}}

{{DEFAULTSORT:Sen, Nikhil Ranjan}}
[[Category:1894 births]]
[[Category:1963 deaths]]
[[Category:Presidency University, Kolkata alumni]]
[[Category:Bengali mathematicians]]
[[Category:Bengali physicists]]
[[Category:Fellows of the Indian National Science Academy]]
[[Category:20th-century Indian mathematicians]]
[[Category:Scientists from Kolkata]]
[[Category:University of Calcutta alumni]]
[[Category:Academic staff of the University of Calcutta]]
[[Category:Indian theoretical physicists]]
[[Category:20th-century Indian physicists]]

Nikhil Ranjan Sen - Revision history

Cornelius R: Adding basic entry and citations.