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## Summary:

- Why does a Lagrangian matter for the standard model?

Hi,

I don't know much about the standard model but I'm asking out of interest. Why do we actually need a Lagrangian for the standard model? Surely when you apply the relevant Euler-Lagrange equations, you end up with a variety of equations like the Maxwell equations or Dirac equations. Why can't we just have those - why do we have to put them all into a Lagrangian?

For instance, why is it important that we have a Lagrangian for the Maxwell field? Why can't we just have Maxwell's equations?

Thanks!

I don't know much about the standard model but I'm asking out of interest. Why do we actually need a Lagrangian for the standard model? Surely when you apply the relevant Euler-Lagrange equations, you end up with a variety of equations like the Maxwell equations or Dirac equations. Why can't we just have those - why do we have to put them all into a Lagrangian?

For instance, why is it important that we have a Lagrangian for the Maxwell field? Why can't we just have Maxwell's equations?

Thanks!