On this day, Albert Einstein received a letter from a physicist in India. The writer, who turned out to be Satyendra Nath Bose, had described himself as a “complete stranger” and had sent Einstein an article for his “perusal and opinion”. Bose was then a reader in the physics department of the University of Dhaka.

The five-page article claimed that it was addressing a flaw in quantum theory. Einstein, who was then at the University of Berlin and had been working on the problem himself, realised that Bose had solved it, deriving his theory from Planck’s law, which states that electromagnetic radiation from a heated body is not emitted continuously, but is composed of units or quanta of energy, the size of which is related to a physical constant. Bose wrote the paper without any reference to classical physics.

Einstein and Bose collaborated, which led them to predict the phenomenon known as “Bose-Einstein condensation”. The exchange between the two is considered fundamental to the development of physics.

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