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.

After passing the intermediate examination in 1911, he studied honors mathematics in Presidency College in Calcutta, where he had Saha and Satyendranath Bose as classmates.

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.

[9] Under von Laue, Sen received a Ph.D. from the University of Berlin for a general relativity dissertation on the boundary conditions for the gravitational field equations on surfaces of discontinuity.

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.

[8] After returning home in 1924, he was appointed as "Rasbihari Ghosh Professor" in the newly formed Department of Applied Mathematics of Calcutta University.

Sen started working on the internal constitution of stars around 1940, after Hans Bethe established the law of energy generation.

Roy gave a singularity-free analytical method that strictly satisfied all the necessary conditions and could be fitted to the field of expanding universe.