Expressing The Dirac Equation
In natural units, the Dirac equation may be written as
where ψ is a Dirac spinor. Here, if were an ordinary 4-vector, then it would pick out a preferred direction in spacetime, and the Dirac equation would not be Lorentz invariant.
Switching to Feynman notation, the Dirac equation is
Applying to both sides yields
which is the Klein–Gordon equation. Thus, as the notation suggests, the Dirac particle has mass m.
Read more about this topic: Gamma Matrices
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