  Starting from the geometric calculus based on Clifford algebra, the idea that
physical quantities are Clifford aggregates ("polyvectors") is explored. A
generalized point particle action ("polyvector action") is proposed. It is
shown that the polyvector action, because of the presence of a scalar (more
precisely a pseudoscalar) variable, can be reduced to the well known,
unconstrained, Stueckelberg action which involves an invariant evolution
parameter. It is pointed out that, starting from a different direction, DeWitt
and Rovelli postulated the existence of a clock variable attached to particles
which serve as a reference system for identification of spacetime points. The
action they postulated is equivalent to the polyvector action. Relativistic
dynamics (with an invariant evolution parameter) is thus shown to be based on
even stronger theoretical and conceptual foundations than usually believed.
