H. David Politzer, Asymptotic Freedom, and Strong Interaction
H. David Politzer has won the 2004 Nobel Prize in Physics ‘for the discovery of asymptotic freedom in the theory of the strong interaction'. ‘Politzer, a professor of theoretical physics at the California Institute of Technology, shares the prize with David Gross and Frank Wilczek. The key discovery celebrated by [the] prize was made in 1973, when Politzer, a Harvard University graduate student at the time, and two physicists working independently from Politzer at Princeton University–Gross and his graduate student 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.'
"The following information [from The Discovery of Asymptotic Freedom] was written by Caltech's MacArthur Professor of Theoretical Physics John Preskill, a colleague of Politzer's. Preskill prepared the text upon learning that Politzer had won the Nobel Prize ...:
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.
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?
The discovery of asymptotic freedom provided a highly satisfying resolution of this puzzle. The calculations of Gross, Wilczek, and Politzer showed that in quantum chromodynamics (QCD), quarks are held together strongly when separated by a distance comparable to the size of a proton, explaining quark confinement. Yet for the smaller separations explored in the high-energy SLAC experiments, the attraction is weaker, supporting Feynman's proposal."
Additional information about H. David Politzer, asymptotic freedom, and strong interaction is available in full-text articles and on the Web.
Reliable Perturbative Results for Strong Interactions? Physical Review Letters, Vol. 30, Issue 26; 1973
Possible Non-Regge Behavior of Electroproduction Structure Functions; Physical Review D, Vol. 10, Issue 5; 1974
Spontaneous Symmetry Breaking in the O(N) Model for Large N; Physical Review D, Vol. 10, Issue 8; 1974
Heavy Quarks and Long-lived Hadrons; Physical Review D, Vol. 12, Issue 5; 1975
Experimental Characteristics of Dynamical Pseudo Goldstone Bosons; Physical Review Letters, Vol. 43, Issue 23; 1979
Additional Web Pages:
Our Man on the Manhattan Project – Politzer and the film "Fat Man and Little Boy", a story about the Manhattan Project; Caltech News