Harry J. Lipkin forgets or disparages the important role of theorists in some crucial experiments in modern particle physics. Unfortunately, such an ahistorical view by a well-known particle physicist feeds into the present misunderstanding of science in some segments of academia, and should not be left uncorrected.
Lipkin asks, “How would physics have progressed in the second half of the 20th century … if theorists had been ignored?” and gives as one of his “who-ordered-that” experiments the discovery of charge conjugation–parity (CP) violation in neutral K decays. But in his Nobel Prize acceptance speech, Val Fitch said, “It is difficult to give a better example of the mutually complementary roles of theory and experiment than in telling the story of the neutral K meson,” which culminated in the discovery of CP violation. 1 In fact, one of the main aims of this experiment was to test the theoretical proposal of Lev Landau and others that CP is conserved in the weak interactions.
“The theoretical establishment was again confounded by the discovery of scaling,” Lipkin continues. This is correct, but he fails to point out that this discovery was made possible because a theorist, James D. Bjorken, suggested plotting the inelastic electron scattering data using a scaling variable that he had introduced earlier on. 2
Lipkin also claims that “the discovery of two kinds of neutrinos was also motivated not by theorists,” but this is incorrect. The search for a second neutrino was motivated by a theoretical puzzle that was first pointed out by theorist Gerald Feinberg: The muon does not decay into an electron and a gamma ray as expected from a single neutrino hypothesis. 3 Subsequently, theorists predicted the existence of a third neutrino, the tau neutrino, which apparently has now been observed at Fermilab. Indeed, the only example given by Lipkin in which theoretical guidance did not play a direct role was the unexpected discovery of the J/psi. There are other such examples, notably Martin Perl’s discovery of the tau lepton, 4 but their existence does not support Lipkin’s broad generalization that “theorists are often irrelevant.”
Seeking the answer to Lipkin’s question, “What guides their [experimenters’] explorations?” one needs to look no further than the accounts given by the discoverers themselves, who invariably acknowledged the important contribution of theorists. 1–4
