John Lighton Synge (; 23 March 1897 – 30 March 1995) was an Irish mathematician and physicist, whose seven-decade career included significant periods in Ireland, Canada, and the USA. He was a prolific author and influential mentor, and is credited with the introduction of a new geometrical approach to the theory of relativity. Background Synge was born 1897 in Dublin, Ireland, into a prominent Church of Ireland family. He attended St. Andrew's College, Dublin and in 1915 entered Trinity College Dublin (TCD). He was elected a Foundation Scholar his first year, which was unusual as it was normally won by more advanced students. While an undergraduate at TCD, he spotted a non-trivial error in Analytical Dynamics, a textbook by E. T. Whittaker, who had recently taught there, and notified Whittaker of the error. In 1919 he was awarded a B.A. in Mathematics and Experimental Physics, and also a gold medal for outstanding merit. In 1922 he was awarded an M.A., and in 1926 a Sc.D., the latter upon submission of his published papers up to then. In 1918, Synge had married Elizabeth Eleanor Mabel Allen (1896–1985). She was another student at TCD, first of mathematics, then of history, but family finances forced her to leave without graduating. Their daughters Margaret (Pegeen), Cathleen and Isabel were born in 1921, 1923 and 1930 respectively. The middle girl grew up to become the distinguished Canadian mathematician Cathleen Synge Morawetz. Synge's uncle John Millington Synge was a famous playwright. He is more distantly related to the 1952 Nobel prizewinner in chemistry Richard Laurence Millington Synge. He was a great-great-great-grandson of the mathematician and bishop Hugh Hamilton. His older brother, Edward Hutchinson Synge (1890-1957), who was known as Hutchie, also won a Foundation Scholarship in Trinity for Mathematics, though he never graduated. While Hutchie's later independent research was long overlooked, he is now recognised for his pioneering work in optics, particularly in near field optical imaging. He died on 30 March 1995 in Dublin. Career in mathematics and physics Synge was appointed to the position of lecturer at Trinity College, and then accepted a position at the University of Toronto in 1920. From 1920 until 1925, Synge was an assistant professor of mathematics at the University of Toronto. There he attended lectures by Ludwik Silberstein on the theory of relativity, stimulating him to contribute "A system of space-time co-ordinates", a letter in Nature in 1921.