Robert Schumann is said to have once remarked about Johann Sebastian Bach: "Let The Well-Tempered Clavier be your daily bread, and you will surely attain good musicianship." Particle physics theorists feel similarly about Sidney Coleman, who died on 18 November, aged 70.
Sidney was a brilliant theoretical physicist. He graduated from the Illinois Institute of Technology in 1957 and went on to graduate school at Caltech, where he studied with Murray Gell-Mann. In the early 1960s, he was a leader in the application of Gell-Mann's revolutionary idea of approximate SU(3) symmetry of the strong interactions. His work on scale invariance and renormalization in the late 1960s and 1970s paved the way for QCD, leading to the discovery by his student David Politzer and others of asymptotic freedom as well as to his idea of dimensional transmutation. In the late 1970s and 1980s, the results and the techniques from his work on vacuum decay were crucial for the beginnings of quantitative cosmology. Throughout his life, he was the leader in educating high-energy theorists about the field-theoretic and symmetry tools that revolutionized the field in the 1970s and led to the development of the Standard Model.
For 40 years, Sidney was the guru of relativistic quantum field theory. He had about 40 PhD students, many of whom became leaders in the field of high-energy theory. However, his influence extended far beyond his academic progeny. Many hundreds of students from all over the Boston area were inspired by his courses on quantum field theory, and his notes were used in courses throughout the world. Many more high-energy theorists, both aspiring and established, pored over his classic papers and summer-school lectures. Like the works of Bach, these were simply perfect. Sidney laboured over them until no word was out of place and no explanatory or pedagogical opportunity was missed.
While his first love was the teaching of graduate-level quantum field theory, Sidney also gave brilliant undergraduate lectures. This was a personal sacrifice, because he was renowned for doing his best work in the wee hours of the morning, and it was never clear whether he was better off getting a few hours of sleep before a late morning undergraduate class, or simply staying up for it. Some of these lectures survive as recordings, such as his colloquium-level lecture, "Quantum Mechanics in Your Face". His lectures were not only clear, beautifully constructed and delivered, they were always very funny. His sharp wit also shone through in the titles of some of his classic papers, such as Why There Is Nothing Rather Than Something… and Black Holes as Red Herrings…
Sidney's wit could be as biting as it was brilliant, and his friends bore the brunt of this – and loved it. They could count on him to keep their head-sizes under control. "Courtesy," Sidney argued, "is for strangers. Kindness is for friends."
Not a cloistered academic, Sidney was also a public intellectual in the best sense. He had a deep interest in science fiction, and wrote and published science fiction criticism himself. He served behind the scenes as a science advisor to a number of movies and programmes for Nova.
Health problems bedevilled the end of Sidney's life and deprived the world of what would surely have been an affectionately irreverent elder statesmanship. He is survived by his wife of 25 years, Diana Coleman, his brother, Robert Coleman, and his many friends around the world.
Howard Georgi, Harvard University.