The equation of motion in Kaluza-Klein cosmology and its implications for astrophysics.

In view of the widespread interest in Kaluza-Klein theory, we derive the fully general equation of motion of a particle (charged or neutral) moving in a spacetime augmented by one extra dimension. We find that extra terms may be present which can have significant astrophysical implications, notably for the peculiar velocities of galaxies. Observations of the latter can in principle be used to decide if the universe has four or five dimensions.