Gauge equivalent universes in 5d Kaluza-Klein theory

We examine in the framework of 5d Kaluza-Klein theory the gauge equivalence of $x^5$-dependent cosmological solutions each of which describes in the 4d sector an arbitrarily evolving isotropic, homogeneous universe with some pure gauge. We find that (1)within a certain time scale $\tau_c$ (which is characterized by the compactification radius $R_c$) any arbitrarily evolving 4d universe is allowed to exist by field equations, and these 4d universes with appropriate pure gauges are all gauge equivalent as long as they are of the same topology. (2)Outside $\tau_c$ the gauge equivalence disappears and the evolution of the universe is fixed by field equations.