spherically symmetric space-timeとは 意味・読み方・使い方

A spherically symmetric spacetime is a spacetime whose isometry group contains a subgroup which is isomorphic to the (rotation) group SO(3) and the orbits of this group are 2-dimensional spheres (2-spheres). The isometries are then interpreted as rotations and a spherically symmetric spacetime is often described as one whose metric is "invariant under rotations". The spacetime metric induces a metric on each orbit 2-sphere (and this induced metric must be a multiple of the metric of a 2-sphere).