Where has the fifth dimension gone?

Abstract

We show that a simple solution to the vacuum field equations of general relativity in 4 + 1 space-time dimensions leads to a cosmology which at the present epoch has 3 + 1 observable dimensions in which the Einstein-Maxwell equations are obeyed. The large ratio of the electromagnetic to gravitational forces is a consequence of the age of the Universe, in agreement with Dirac's large-number hypothesis.