nprofile1qy2hwumn8ghj7un9d3shjtnddaehgu3wwp6kyqpquhnx67vlf04mwtt7qrjyx47gpmtf3twz4nrfmx9lspw6rrv5gkhss5m2ru (nprofile…m2ru) - I don't know exactly what a 'layer' is, but:
Take a nice theory like QED or the Standard Model. To compute the answer to any physical question we should sum over 'all' Feynman diagrams contributing to the answer. We don't know how to do that, and the sum would almost surely diverge if we tried. So instead we try to sum over all diagrams with at most some number of loops and/or vertices.
But first, we need to see what summing over such diagrams would predict for low-energy experiments to measure the electron's charge, mass, etc.! We do this calculation to choose the parameters in our theory - we need to choose the parameters to make sure we get the right answer to *those* questions!
Then, once we've chosen the parameters in our theory this way, we can compute the answer to our actual question, summing over diagrams with at most some number of loops and/or vertices.
The principal is not so complicated, but actually doing the calculations is a massive pain, and there are some choices involved.
For the best existing computation of the magnetic moment of the electron, Kinoshita added up 12672 Feynman diagrams!
https://arxiv.org/abs/1205.5368
John Carlos Baez /
npub17u…8pd6m
2025-01-01 03:46:48
in reply to nevent1q…xjjj
Author Public Key
npub17u6xav5rjq4d48fpcyy6j05rz2xelp7clnl8ptvpnval9tvmectqp8pd6mPublished at
2025-01-01 03:46:48Event JSON
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