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Basic QED question

  1. Jul 25, 2010 #1
    In the Eric Weissteins's World of Physics entry on "Quantum Electrodynamics" he gives one of the governing equations as


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


    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]?


    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!
    Last edited: Jul 25, 2010
  2. jcsd
  3. Jul 26, 2010 #2


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    Re: test

    Yes, they are the [itex] \alpha [/itex] and the [itex] \beta [/itex] of Dirac.
  4. Jul 26, 2010 #3


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    Thread title has been changed.

  5. Jul 27, 2010 #4
    Thanks to you both.

    I just noticed something. Is there a typo in that equation? I checked again and the way I entered it is exactly how it appears on the Weisstein page


    but it looks like the dimensions of the second term on the left hand side - leaving out the wave function itself -


    c \mathbf {a} (- \frac {e}{c} \mathbf {A} ) = - \mathbf {a} e \mathbf {A}


    are different from the others. It's momentum while the others are energy.
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