Harry J. Lipkin (Physics Today, July 2000, page 15) writes that, on the basis of the past 50 years, scientific progress did not primarily result from experiments designed to check theory. Looking back at the same period, I strongly disagree.
The most exciting results immediately following World War II were the precision atomic experiments verifying the renormalized quantum electrodynamics of Richard Feynman and Julian S. Schwinger. Enrico Fermi’s theory of the weak interaction incorporating Wolfgang Pauli’s neutrino hypothesis predicted the interactions of neutrinos. The famous experiment of Clyde Cowen and Frederick Reines in 1956 was designed exactly to verify this prediction.
Hints from kaon decays led Tsung-Dao Lee and Chen Ning Yang to propose that parity was violated in the weak interaction. This idea led directly to the experiment of C. S. Wu, which showed the asymmetry of the emitted electrons from the decay of a polarized nucleus. Immediately thereafter, the V – A theory was formulated by Feynman and Murray Gell-Mann, and Robert E. Marshak and E. C. G. Sudarshan; a whole series of experiments that followed verified this theory, particularly precision experiments on muon decay.
Although the V – A theory was successful, except for the mystery of charge conjugation–parity (CP) violation, it was theoretically unsatisfactory because of its divergence problem. Steven Weinberg and Abdus Salam were then led to propose the spontaneously broken gauge theory. To check this, an experimental search for the predicted neutral currents in neutrino reactions was carried out, which led to the provisional acceptance of the theory.
Proving that theory required detection of the W and Z bosons, which in turn required construction of the proton collider at CERN. The theory was precision-tested by electron–positron colliders built specifically for this purpose: the Large Electron Positron Collider (LEP) at CERN and the Stanford Linear Collider at SLAC.
As a result of many experiments, we now have a Standard Model that describes nearly all observed elementary particle phenomena in terms of a Hamiltonian that can be written on one line. Current experiments at B-meson factories are designed to test whether this theory also explains CP violation.
We do not have a theory of everything, although some of my colleagues dream of one. When new domains of energy are explored, we will not be surprised to discover that there are things in the heavens and on Earth that are not described by our present theory. Our goal, then, must be to find a more encompassing theory and design experiments to fully test it. That, I believe, is the scientific method.
