Friedmann-Lemaitre-Robertson-Walker Metric

The Friedmann-Lemaitre-Robertson-Walker metric, usually abbreviated FLRW, is a metric that describes a homogeneous, isotropic universe that may be expanding, contracting, oscillating, or constant in size. It provides the mathematical framework for modeling a universe that has uniform density and looks the same in every direction from any vantage point, an assumption known as the cosmological principle. The metric follows from applying Einstein's field equations of general relativity under that same cosmological principle, and it underlies the standard model of cosmology.