Cao replies: The scholarship of a scientific biography is mainly judged by its analysis and assessment of the subject’s scientific legacy. Julian Schwinger’s legacy lies primarily in the foundations of fundamental physics: his operator formalism of quantum field theory, combined with a renormalization scheme; and his motivations and justifications in searching for a new scheme—the source theory—that has great impact on the conception of effective field theories. This paradoxical legacy has been extensively explored over the past two decades, 1 but was virtually untouched by Mehra and Milton. That insensitivity explains their failure to properly treat Schwinger’s works about scaling, asymptotic freedom, and quantum chromodynamics—works that were dictated by his foundational concerns.
With one exception, Mehra and Milton call the inaccuracies in their conceptual understanding and historical details mentioned in my review “insubstantial failings.” The exception, they say, “is important,” and they disagree with me on that one: In the review, I wrote, “To say that in 1964 ‘the approximation symmetry group was not yet established’ directly contradicts the historical facts: Since 1959, Sheldon Glashow and Murray Gell-Mann were publishing on the subject in terms of the soft-mass problem.” Mehra and Milton rebut that statement by claiming that “the flavor SU(3) symmetry … was not generally accepted until … 1964.” Their rebuttal, ironically, demonstrates that they still do not understand that the two notions are not identical. For Glashow, the approximation symmetry group mainly referred to a softly-broken gauge symmetry rather than the flavor symmetry. That is why I mentioned the soft-mass that was designed by Glashow 2 to break the gauge symmetry softly.
