Also, General Relativity defines non-inertia space-time as a space of Riemann. For Riemann space has positive curvature, we have to doubt about where the minus curvature space is.

• 广义相对论把非惯性时空定义为黎曼空间,但由于黎曼几何是正曲率空间,既然广义时空是对称的,我们必然要问,负曲率空间到哪去了?