Here is how I remember it. Supposedly I was a particle physicist: indeed I had spent three years as a graduate student in Cornell (1962–1965) and a year as a postdoc in Berkeley (1965–1966), learning about S-matrix theory, and hating every minute of it. The general opinion among leaders of the field was that hadronic length and time scales were so small that in principle it made no sense to probe into the guts of a hadronic process – the particles and the reactions were unopenable black boxes. Quantum field theory was out; Unitarity and Analyticity were in. Personally, I so disliked that idea that when I got my first academic job I spent most of my time with my close friend, Yakir Aharonov, on the foundations of quantum mechanics and relativity.

By 1967 I was convinced that the S-matrix black-box view was wrong-headed. I had spent a lot of time formulating relativistic quantum theory in what was then called the infinite-momentum frame (IMF), now called the light-cone frame. The idea that appealed to me was that by boosting a system to very large momentum you could slow down its internal motions. By stationing a sequence of detectors along the direction of the boost, one could imagine probing an interacting system of hadrons as it evolved. I wrote a lot of papers showing among other things that physics in the IMF had a Galilean symmetry so that the ordinary rules of nonrelativistic quantum mechanics must apply.

The landscape

The world-view shared by most physicists is that the laws of nature are uniquely described by some special action principle that completely determines the vacuum, the spectrum of elementary particles, the forces and the symmetries. Experience with quantum electrodynamics and quantum chromodynamics suggests a world with a small number of parameters and a unique ground state. For the most part, string theorists bought into this paradigm. At first, it was hoped that string theory would be unique and explain the various parameters that quantum field theory left unexplained. When this turned out to be false, the belief developed that there were exactly five string theories with names like ‘type 2a’ and ‘heterotic’. This also turned out to be wrong. Instead, a continuum of theories were discovered that smoothly interpolated between the five and also included a theory called ‘M-theory’. The language changed a little. One no longer spoke of different theories, but rather of different solutions of some master theory.

The space of these solutions is called the ‘moduli space of supersymmetric vacua’. I will call it the ‘supermoduli-space’. Moving around on this supermoduli-space is accomplished by varying certain dynamical ‘moduli’. Examples of moduli are the size and shape parameters of the compact internal space that 4-dimensional string theory always needs. These moduli are not parameters in the theory, but are more like fields. As you move around in ordinary space, the moduli can vary and have their own equations of motion.

In this chapter I present a personal reminiscence of the development of our current ideas about quark confinement. I describe what I remember of my own involvement and that of the people who influenced me. If others remember it differently, I hope they will not be too angry.

By the end of the 1960s our empirical knowledge of hadrons consisted of a vast mountain of data about their spectrum, their low- and high-energy interactions, and their electromagnetic and weak properties. To some extent the story of the eventual interpretation in terms of QCD was like digging a tunnel through the mountain with crews of diggers starting independently at the two ends. At one end was the short-distance behavior of local currents and its interpretation in terms of freely moving quark-parton constituents. At the other end was the low-momentum-transfer Regge structure including a spectrum of highly excited rotational states, shrinking diffraction peaks, and multihadron final states of peripheral collisions, but no free quarks. Sometime in 1973 the two tunnel crews discovered that they had met and a complete picture of the strong interactions existed. Of course the two crews were not entirely unaware of each other. The Regge workers were beginning to organize the trajectories by quantum numbers suggested by the quark model. Eventually, the Regge picture culminated in 1968 with a set of scattering amplitudes based on the duality principle of R. Dolen, D. Horn, and C. Schmidt.