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## Main Question or Discussion Point

In the Eric Weissteins's World of Physics entry on "Quantum Electrodynamics" he gives one of the governing equations as

[tex]

[ c \mathbf{a} ( -i \hbar \nabla - \frac {e}{c} \bf {A} ) + bmc^2 ] \psi = ( i \hbar \frac {\partial}{\partial t} - e \phi ) \psi

[/tex]

but doesn't define

Thanks.

Edit: Oops - sorry about the title of this thread! I meant to call it something like, "basic QED question" but I was testing the LaTeX first and forgot to change it, and now that it's up I don't know how to!

[tex]

[ c \mathbf{a} ( -i \hbar \nabla - \frac {e}{c} \bf {A} ) + bmc^2 ] \psi = ( i \hbar \frac {\partial}{\partial t} - e \phi ) \psi

[/tex]

but doesn't define

**a**or b. Are these the Dirac matrices, with**a**= { [itex] \alpha_1, \alpha_2, \alpha_3 [/itex] } and b = [itex] \alpha_4 [/itex]?Thanks.

Edit: Oops - sorry about the title of this thread! I meant to call it something like, "basic QED question" but I was testing the LaTeX first and forgot to change it, and now that it's up I don't know how to!

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