Leonard Susskind concludes the course by generalizing the presentation of the quantum field theory for spin-1/2 fermions to three dimensions, and demonstrating that the mass of fermions originates from the cross term between the two chiralities in the Dirac equation.

Leonard Susskind develops the quantum field Hamiltonian, and then derives the Dirac equation for fermions. Dirac's theory of fermions was the first to incorporate special relativity into the development of quantum mechanics.