#### samalkhaiat

Science Advisor

- 1,615

- 804

It would be so nice if this is true. Unfortunately, the interaction Lagrangian [itex]A_{\mu}J^{\mu}[/itex] cannot be expressed in terms of the [itex]F_{\mu\nu}[/itex].In the classical theory what's measurable are only the field strengths, i.e., ##F_{\mu \nu}=\partial_{\mu} A_{\nu}-\partial_{\nu} A_{\mu}##, andyou can express everything in terms of this gauge-invariant field-strength tensor.