| Scale factor in Robertson-Walker metric |

| | As I understand it, the R-W metric allows BB theorists to model an ideal expanding **universe** that is homogeneous and isotropic, and that the **scale** **factor's** base values are set at 1 for present time and at 0 for the BB singularity. |

| | If you believe that redshift is primarily due to cosmological expansion, the **scale** **factor** allows you to extrapolate the present separation of a distant galaxy based on the presumed cosmological expansion rate and the estimated time that has passed since the emission of the light that we just received. |

| | Once we know what fraction of the total content of the **universe** is relativitic, non-relativistic, cosmological constant or dark energy etc., and the value of curvature constant k, (which says how the **universe** is curved; it depends on the total density of the **universe**) we get an expression for the **scale** **factor**. |

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