Universe Expansion in Spatially Flat Universes

The expansion of the universe is a first-level issue in astrophysics. Knowing how it expands, its scale factor, allows us to solve a multitude of problems that we could not solve otherwise. Experimental data concerning the curvature of our universe show us that its spatial curvature is very close to zero, that is, our universe can be considered spatially flat. The most relevant cosmological models take this data into account. Here we have studied the expansion in a supposed universe model with FLRW metric and zero spatial curvature and we have come to the conclusion that in this assumption the expansion is always linear. Thus, we have shown that the scale factor in spatially flat universes with FLRW metric, is a linear function.

Keywords: General Relativity, Cosmos, Spatially Flat Universe.