Chew was known as a leader of the S-matrix approach to the strong interaction and the associated bootstrap principle, a theory whose popularity peaked in the 1960s when he led an influential theory group at the University of California, Berkeley. S-matrix theorists sought to understand the strong interaction by using the analytic properties of the scattering matrix to calculate the interactions of bound-states without assuming that there is a point-particle field theory underneath. The S-matrix approach did not provide a local space-time description. Although it was not immediately appreciated by the practitioners, it was a natural framework in which to produce a quantum theory of gravity. Chew's central contribution to the program came in 1961: along with collaborator Steven Frautschi, they noted that the mesons fall into families where the square of the mass of a meson is linearly proportional to the spin, with the same constant of proportionality for each of the families. Since bound states in quantum mechanics naturally fall into families of this sort, their conclusion, quickly accepted, was that none of the strongly interacting particles were elementary. The conservative point of view was that the bound states were made up of elementary particles, but Chew's more far-reaching vision was that there would be a new type of theory which describes the interactions of bound-states which have no point-like constituents at all. This approach was sometimes called nuclear democracy, since it avoided singling out certain particles as elementary.
Legacy
Although the S-matrix approach to the strong interactions was largely abandoned by the particle physics community in the 1970s in favor of quantum chromodynamics, a consistent theory for the scattering of bound-states on straight-line trajectories was eventually constructed and is nowadays known as string theory. Within string theory, Edward Witten reinterpreted S-matrix theory as a flat-space statement of the holographic principle. Professor Chew also participated in religion and science discussions. He stated that an "appeal to God may be needed to answer the 'origin' question, 'Why should a quantum universe evolving toward a semiclassical limit be consistent?'" Chew investigated into models in which the concept of happenings or events play a fundamental role, not only particles. He saw similarities among his approach and the notion of occasion of Alfred North Whitehead.
