  We develop a trajectory construction of solutions to the massless wave
equation in n+1 dimensions and hence show that the quantum state of a massive
relativistic system in 3+1 dimensions may be represented by a stand-alone
four-dimensional congruence comprising a continuum of 3-trajectories coupled to
an internal scalar time coordinate. A real Klein-Gordon amplitude is the
current density generated by the temporal gradient of the internal time.
Complex amplitudes are generated by a two-phase flow. The Lorentz covariance of
the trajectory model is established.
