The equation often described as “the one that runs the universe” is the first Friedmann equation, derived from Einstein’s General Relativity.  It is considered the most important equation in cosmology because it describes how the universe expands over time based on its contents.  (aa˙​)2=38πG​ρ−a2kc2​+3Λc2​ This equation relates the expansion rate of the universe (left side, involving the scale factor a ) …

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