Of the four fundamental forces–the others besides the strong nuclear force are electromagnetism, the weak nuclear force (responsible for the decay of radioactive nuclei), and gravitation–the strong force was by far the most poorly understood in the early 1970s. It had been suggested in 1964 by Caltech physicist Murray Gell-Mann that protons and neutrons contain more elementary objects, which he called quarks.
Wilczek–theorized that quarks actually become bound more tightly the farther they get from each other.
This discovery has been known for 31 years as "asymptotic freedom," and is often described by physics professors to their students with the analogy of a rubber band increasing in tightness as it is pulled apart. Asymptotic freedom established quantum chromodynamics (QCD) as the correct theory of the strong force, one of the four fundamental forces of nature.'
Yet isolated quarks are never seen, indicating that the quarks are permanently bound together by powerful nuclear forces. Meanwhile, studies of high-energy collisions between electrons and protons performed at the Stanford Linear Accelerator Center (SLAC) had probed the internal structure of the proton, and Caltech's Richard Feynman had suggested in 1969 that the results of these experiments could be explained if quarks inside a proton are nearly free, not subject to any force. Feynman's suggestion, together with the observation that quarks are unable to escape from nuclear particles, posed a deep puzzle: how could nuclear forces be both strong enough to account for the permanent confinement of quarks and weak enough to account for the SLAC experiments?
David Politzer, Asymptotic Freedom, and Strong InteractionPhys. Rev. D 10 (1974): Sidney Coleman, R. Jackiw, and H. D. Politzer - Spontaneous symmetry breaking in...
