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.