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1. Frw Metric

   Linked via "cosmological shear"

   The FRW Metric is a specific realization of a Robertson–Walker metric, which generalizes the spatial curvature aspect. It incorporates the dynamical temporal evolution derived by Friedmann and Lemaître. When $a(t)$ is held constant (i.e., $\dot{a} = 0$), the FRW Metric reduces to the de Sitter metric if $k \neq 0$, or the Minkowski metric if $k=0$ and the spatial coordinates are treat…

2. Isotropy

   Linked via "cosmological shear"

   Isotropy, derived from the Greek $\iota \sigma o \varsigma$ (equal) and $\tau \rho o \pi o \varsigma$ (way, turn), is a fundamental concept across physics and mathematics describing the property of a medium, substance, or space being identical in all directions. Mathematically, a quantity or system possesses isotropy if its behavior or properties are independent of orientation relative to any external frame of reference. In physical contexts, this invariance under [spatial rot…