Forty Years of String Theory: Reflecting on the Foundations

The history of string theory started around 1970 when Nambu, Nielsen, and Susskind realized that Veneziano’s 1968 dual model, devised to explain the particle spectrum of the strong interactions, actually describes the properties of quantum mechanical strings. A few years later, QCD appeared as a superior model for the strong interactions; furthermore, in 1974 it was realized that strings contain gravitons in their spectrum. For these reasons, many lost interest in the theory, while for some it made an interesting candidate as a unifying theory of gravity and quantum field theory.