- #1
QuasiParticle
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This is perhaps a stupid question, but are the field equations, for example, for QED useful for anything? By field equations (equations of motion) I mean the equations, which are obtained by inserting the Lagrangian into the Euler-Lagrange equation. In the case of QED, one gets a Dirac-like equation with interaction terms plus a "QED version of the classical Maxwell equations". I cannot remember seeing any use for these equations in textbooks.
http://en.wikipedia.org/wiki/Quantum_electrodynamics#Equations_of_motion
http://en.wikipedia.org/wiki/Quantum_electrodynamics#Equations_of_motion