 In making spacetime curvature dependent on distributions of mass and energy, general relativity is indeed capable of encompassing all (non-quantum) physical fields. However, in classical general relativity there remains a fundamental asymmetry between gravitational and non-gravitational fields, in particular, electromagnetism, the only other fundamental physical interaction definitely known until the 1930s. This shows up visibly in one form of the Einstein field equations in which, on the left-hand side, a geometrical object (\(G_{\mu\nu}\), the Einstein tensor) built up from the uniquely compatible linear symmetric (“Levi-Civita”) connection associated with the metric tensor \(g_{\mu\nu}\), and representing the curvature of spacetime, is set identical to a tensorial but non-geometrical phenomenological representation of matter on the right-hand side.