  Standard formulation is unable to distinguish between the (+++-) and (---+)
spacetime metric signatures. However, the Clifford algebras associated with
each are inequivalent, R(4) in the first case (real 4 by 4 matrices), H(2) in
the latter (quaternionic 2 by 2). Multivector reformulations of Dirac theory by
various authors look quite inequivalent pending the algebra assumed. It is not
clear if this is mere artifact, or if there is a right/wrong choice as to which
one describes reality. However, recently it has been shown that one can map
from one signature to the other using a "tilt transformation" [see P. Lounesto,
"Clifford Algebras and Hestenes Spinors", Found. Phys. 23, 1203-1237 (1993)].
The broader question is that if the universe is signature blind, then perhaps a
complete theory should be manifestly tilt covariant. A generalized multivector
wave equation is proposed which is fully signature invariant in form, because
it includes all the components of the algebra in the wavefunction (instead of
restricting it to half) as well as all the possibilities for interaction terms.
