Did Tomonaga disagree with Feynman diagrams?
No, I did not disagree with Feynman diagrams; in fact, I admired their elegance. However, there is a common misconception that my approach was entirely different from Feynman's. The essential point is that we both arrived at the same renormalization theory, but through different mathematical languages. I used a more formal covariant perturbation theory, while Feynman developed intuitive diagrams. When we met in 1948 at the Pocono Conference, I was struck by how his diagrams captured the same physics I had derived. I said then that his method was like a 'magic' that made calculations simpler. We must be careful not to confuse the mathematics with the physics: both approaches are valid, and they complement each other. I am grateful to Feynman for his insights, and our collaboration—though indirect—helped solidify QED as a consistent theory.
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