Linked from
The 16 pages that link to Friedmann–Lemaître–Robertson–Walker metric, each with the reason it gives.
Cosmological principleRelated: This metric encodes the spatial symmetries assumed by the principle.
Friedmann equationsRelated: This metric supplies the geometry assumed in their derivation.
Flatness problemRelated: It separates spatial curvature from the universe’s changing scale factor.
3-sphereRelated: Its positively curved spatial slices have the geometry of a 3-sphere.