  We discuss a new feature of the 5d Kaluza-Klein cosmology. For that purpose,
we obtain the simplest x^5-dependent solution which, in the reduced
description, is associated with a radiation-dominated Robertson-Walker
universe, and also can be regarded as an extension of the Schwarzschild
solution. This solution enables us to deduce an important result that an
evolving universe is related with a static universe by the gauge
transformation, i.e., they are gauge equivalent. This means that having a
different universe simply corresponds to choosing a different gauge
