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## Summary:

- QED describes all physics under certain energy level. So how we derive results that we know from QM from QED?

## Main Question or Discussion Point

**Summary:**QED describes all physics under certain energy level. So how we derive results that we know from QM from QED?

I want to know how to get quantum mechanics from QED (Quantum Electrodynamics).

In QED we showed that the potential between two electrons goes like 1/r as in quantum mechanics, but it's not enough since there are other computations in advanced quantum mechanics course which I don't know ho to derive from QED. For example, calculating lifetime of transition levels, like 2p to 1s. Since QED describes all the interactions (relevant) I want to know how to derive that. Is there a good book that explains that?