It is possible that null paths in 5D appear as the timelike paths of massive
particles in 4D, where there is an oscillation in the fifth dimension around
the hypersurface we call spacetime. A particle in 5D may be regarded as
multiply imaged in 4D, and the 4D weak equivalence principle may be regarded as
a symmetry of the 5D metric.Comment: 15 pages, in press in Phys. Lett.