there is just one electron field and all electrons are understood as excitations of this electron field.

]]>I just began reading your book.

Could you possibly clarify a confusion for me.

You wrote on page 24, “an elementary excitation of the electron field is what we call the electron.”.

What bothers me is this: Say, an electron in orbit around an atom gets excited. This means the excited electron was part of the electron field.

Is this electron field local to that atom or non-local to all possible existing electrons everywhere?

2. The normalization condition in Eq. 3.9 is without complex conjugation. The Minkowski product of two four-vectors only involves transposition and the Minkowksi metric.

Hope this helps and let me know if you have any further questions!

]]>2. In (3.11) formula, did not we need to take a complex conjugation when writing the left vector? Then the result would be +1, not -1 ]]>

Best regards

Ioannis ]]>

And please let me know if it doesn’t answer your question!

]]>When we derive Euler-Lagrange equations in classical mechanics following the Lagrangian approach we introduce Boundary conditions at the starting- and end-points of the path in the configuration space. Usually,though not necessarily, one requires that q(tinitial)=q(tfinal)=0, see section 4.3 of your book. But the standard problem in classical mechanics is to instead assume Initial (not Boundary) conditions, for instance it is assumed that the initial position q(tinitial) and initial velocity q′(tinitial) are known.

Is there any way to modify the Lagrangian, adding perhaps a total derivative of a function of q and t, such that the extremisation of the Action would yield the Euler-Lagrange equations together with the above mentioned Initial conditions?

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