Asymptotic freedom: From paradox to paradigm

A Pair of Paradoxes

In theoretical physics, paradoxes are good. That's paradoxical, since a paradox appears to be a contradiction, and contradictions imply serious error. But Nature cannot realize contradictions. When our physical theories lead to paradox we must find a way out. Paradoxes focus our attention, and we think harder.

When David Gross and I began the work that led to this Nobel Prize (1–3)† in 1972, we were driven by paradoxes. In resolving the paradoxes, we were led to discover a new dynamical principle, asymptotic freedom. This principle, in turn, has led to an expanded conception of fundamental particles, a new understanding of how matter gets its mass, a new and much clearer picture of the early universe, and new ideas about the unity of Nature's forces. Today I'd like to share with you the story of these ideas.

Paradox 1: Quarks Are Born Free, but Everywhere They Are in Chains. The first paradox was phenomenological.

Near the beginning of the 20th century, after pioneering experiments by Rutherford, Geiger, and Marsden, physicists discovered that most of the mass and all of the positive charge inside an atom is concentrated in a tiny central nucleus. In 1932, Chadwick discovered neutrons, which together with protons could be considered as the ingredients out of which atomic nuclei could be constructed. But the known forces, gravity and electromagnetism, were insufficient to bind protons and neutrons tightly together into objects as small as the observed nuclei. Physicists were confronted with a new force, the most powerful in Nature. Understanding this new force became a major challenge in fundamental physics.

For many years, physicists gathered data to address that challenge, basically by bashing protons and neutrons together and studying what came out. The results that emerged from these studies, however, were complicated and hard …