Velocities in both space and time are formalized and generalized for

-dimensional Euclidean spaces. Applied to photons and mass particles, this implies a dimensional hierarchy between their velocities. It is suggested that mass particles, that are fermions in 4D, behave like bosons in 5D gravity where they follow null geodesics. Some speculations on alternative propulsion mechanisms are made.
PACS 04.50.+h © Copyright 2005-2007 R.F.J. van Linden