QED is the quantum theory of how light and matter interact. It merges Maxwell’s theory of electricity and magnetism with Heisenberg’s and Schrödinger’s quantum theory and Einstein’s special theory of relativity. Feynman was one of the principal architects of QED, and after looking at the structure of his theory, I can see why he had such admiration for calculus. His theory is chock-full of it, both in tactics and in style. It’s teeming with power series, integrals, and differential equations and includes plenty of hijinks with infinity. More important, it’s the most accurate theory anyone has
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