The Indian Contribution to the Physics of Black Holes: 2020 Nobel Prize

Scientific discoveries are not made in vacuum; they all have a background (or shoulders of Giants to stand on in Newton’s pronouncement) to anchor and build on. The famous and powerful singularity theorems of Hawking and Penrose of mid-1960s were strongly anchored on the remarkable Raychaudhri equation discovered in 1953. The most remarkable and profound prediction that followed from the equation was that gravitational collapse would inevitably lead to singularity in Einstein’s theory of gravitation – general relativity. Hawking and Penrose generalized and located this result to a more general setting that Einstein’s equation under very general conditions cannot admit a solution that has no singularity. They proved powerful rigorous mathematical theorems employing the techniques of global analysis that gravitational collapse would not only end up in singularity but before that a black hole would be formed. It is this robust prediction that has won Roger Penrose the 2020 Nobel Prize in Physics. In this note, I will recount the Indian contributions that have gone into making the background.