Dyson series
Expansion of the time evolution operator / From Wikipedia, the free encyclopedia
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In scattering theory, a part of mathematical physics, the Dyson series, formulated by Freeman Dyson, is a perturbative expansion of the time evolution operator in the interaction picture. Each term can be represented by a sum of Feynman diagrams.
This series diverges asymptotically, but in quantum electrodynamics (QED) at the second order the difference from experimental data is in the order of 10ā10. This close agreement holds because the coupling constant (also known as the fine-structure constant) of QED is much less than 1.[clarification needed]