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by evanb
3636 days ago
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This is true if the system you're trying to describe is weakly coupled. If the theory is strongly coupled, then in fact more and more complicated diagrams count more and more. In this case the method of Feynman diagrams because basically useless---in the case you describe you know you can get most of the answer from a simple calculation (of the simplest diagrams). But if more complicated diagrams count more (as in strong coupling) then you don't have a place to start, because whatever diagram you pick to start at I can make more complicated and be confident that my new diagram counts more than the pieces you've computed. In that case we need a different approach, the most generic of which is lattice field theory https://en.wikipedia.org/wiki/Coupling_constant#Weak_and_str... https://en.wikipedia.org/wiki/Lattice_field_theory |
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