# Nobel 2020 winner Roger Penrose’s theory based on Scientist Amal Raychaudhuri’s equation!

No one mentioned Amal Raychaudhuri at the Physics Nobel citation this year when the name of Physicist Roger Penrose was declared as the one who won the 2020 Nobel Prize in Physics - jointly, with Reinhard Genzel and Andrea Ghez - for the discovery that black hole formation is a robust prediction of the general theory of relativity. What a lot of people do not know is his journey to the discovery had a connection to India – to be precise to Kolkata, as his discovery stands on the shoulders of Indian physicist Amal Kumar Raychaudhuri.

**Andrea Ghez and Reinhard Genzel**

**After the Royal Swedish Academy of Sciences awarded one half of the 2020 physics Nobel to Penrose for discovery related to Black Holes, the Raychaudhuri Equation in General Relativity, derived by Raychaudhuri (AKR), has come to the spotlight. Penrose, in collaboration with cosmologist Stephen Hawking, used an equation that Raychauduri had published in the journal Physical Review in 1955, for a mathematical description of Black Holes in 1969. Even though General Relativity had predicted their existence, Einstein himself did not believe in them.**

Raychaudhuri was a professor at Ashutosh College, Kolkata when he was working on the equation in 1950s. The paper was published when he was at the Indian Association for the Cultivation of Science (IACS) in 1955. He had used geometry to arrive at a singularity where Laws of Physics break down and physical quantity becomes infinitely large in the context of gravity and where space time becomes infinitely large.

**Roger Penrose**

Amal Raychaudhuri’s equation was the building block on which the Penrose-Hawking singularity theorems published in 1969 were based. Both Penrose and Hawking have acknowledged Raychaudhuri’s contribution on numerous occasions in published papers and books. But it took time for Raychaudhuri to be recognised at home. Apparently, there were some physicist who were even skeptical when he published the paper. It was only when Soviet physicist, Lev Landau, had also derived the same equation a little later than Raychaudhuri, that the scientific community accepted it as a key contribution. And as usual this Bengali scientist did not find any mention at the Nobel Prize citation.

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