S. F. Gull, A. N. Lasenby and C. J. L. Doran.
Electron Paths, Tunnelling and Diffraction in the Spacetime Algebra
Found. Phys. 23(10), 1329-1356 (1993)
Abstract: This paper employs the ideas of geometric algebra
to investigate the physical content of Dirac's electron theory.
The basis is Hestenes' discovery of the geometric significance of
the Dirac spinor, which now represents a Lorentz transformation
in spacetime. This transformation specifies a definite velocity,
which might be interpreted as that of a real electron. Taken literally,
this velocity yields predictions of tunnelling times through potential
barriers, and defines streamlines in spacetime that would correspond
to electron paths. We also present a general, first-order diffraction
theory for electromagnetic and Dirac waves. We conclude with a critical
appraisal of the Dirac theory.