Now in Boston, Weinberg describes how his earlier work on current algebra led to effective field theory. With the Vietnam War going on, JASON work focuses on the war effort. In 1967, Weinberg takes up a lectureship at MIT and published his most-cited paper, “A Model of Leptons,” which heralded electroweak theory. He attends the Solvay conference in Brussels in 1967, but misses being in the group photo. Back in Boston, Weinberg discusses making friends through his election to the American Academy of Arts and Sciences. He becomes involved in an independent study of the US’ anti-ballistic missile program, concluding that this would hasten the arms race between the US and the Soviet Union.

The pion, the mediator of the nuclear force proposed in 1935 by Yukawa. The first particle discovered in the cosmic rays looked like the pion, but was later found to be a lepton, the muon. Experiments at high altitudes on cosmic rays led finally to the discovery of the pion. More experiments soon showed other surprises, the strange particles.

How the properties of the charged pion have been measured.

The discoveries of the charged leptons and of the neutrinos.

How, in 1928, A. M. Dirac found the fundamental relativistic wave equation and the Dirac Lagrangian. Dirac’s fundamental predictions of the existence for each fermion of an antiparticle with the same mass but opposite ‘charges’. How the positron and the antiproton were discovered. The important concepts of helicity and chirality.

The Majorana equation for completely neutral fermions.