I’ve found it enjoyable recently to track what was happening in mathematics (and physics) 100 (and 50,150,200…) years ago, in the spirit of Scientific American‘s venerable “50, 100, and 150 years ago” column. I got into it last summer when I was reading Abraham Pais’s biography of Einstein and realized that the events I was reading about (Einstein realizing that the correct formulation of general relativity would be through [semi-]Riemannian geometry) took place exactly 100 years previously. It seemed to make it fresh and exciting, making it possible to imagine I was living back then and it was all happening around me.

So what was happening in 1913 in mathematics? Many things, of course, including the tail end of the shift toward highly rigorous axiomatic foundations (Zermelo’s first axiomatic set theory was just 5 years old) and the beginning of the shift toward high abstraction (metric spaces were 7 years old, and Emmy Noether‘s work on abstract algebra was 8 years in the future). And Hilbert, then the leading mathematician, was furiously learning physics to try to beat Einstein to the punch (which he very nearly did). But I want to point out (belatedly) two particular, related anniversaries.

On 16 January 1913, Srinivasa Ramanujan wrote his first letter to English mathematician G. H. Hardy, initiating one of the most fruitful and unusual collaborations in the history of mathematics, one that has a more affecting human story behind it than almost any other. Ramanujan’s work continues to be an inspiration for number theorists—see, for example, the SASTRA Ramanujan Prize.

Coincidentally, one of the mathematicians most closely linked to some of Ramanujan’s work was born just two months after that historic letter was written—and he also has an unusual life story. The famed itinerant number theorist and combinatorist par excellence Paul Erdos was born on 26 March 1913. (WordPress seems not to want to give me the correct double accent mark on the “o”.) Erdos also inspired countless mathematicians, not least because he collaborated with hundreds of them on more papers than anyone but Euler.

I wish I had been paying attention earlier in the year so that I could have celebrated these anniversaries on time, but better late than never. (We can all celebrate Ramanujan’s birthday, which is now officially Indian National Mathematics Day, on 22 December.)

If you want to see a sample of a subject that both Ramanujan and Erdos worked on, check out my videos on “Why 5040 is a cool number“. (Self-promotion achieved!)