 Later in this article you will see scalar-tensor theories that contain a scalar field in addition to the tensors of general relativity, and other variants containing vector fields as well have been developed recently.After general relativity, attempts were made either to improve on theories developed before general relativity, or to improve general relativity itself.Many different strategies were attempted, for example the addition of spin to general relativity, combining a general relativity-like metric with a spacetime that is static with respect to the expansion of the universe, getting extra freedom by adding another parameter.