  The mathematical similarities between non-relativistic wavefunction
propagation in quantum mechanics and image propagation in scalar diffraction
theory are used to develop a novel understanding of time and paths through
spacetime as a whole. It is well known that Feynman's original derivation of
the path integral formulation of non-relativistic quantum mechanics uses
time-slicing to calculate amplitudes as sums over all possible paths through
space, but along a definite curve through time. Here, a 3+1D spacetime wave
distribution and its 4-momentum dual are formally developed which have no
external time parameter and therefore cannot change or evolve in the usual
sense. Time is thus seen "from the outside". A given 3+1D momentum
representation of a system encodes complete dynamical information, describing
the system's spacetime behavior as a whole. A comparison is made to the
mathematics of holograms, and properties of motion for simple systems are
derived.
