 A second example: GTR allows us to model a single rotating object in an otherwise empty universe (e.g., a neutron star). Relationism of the Machian variety says that such rotation is impossible, since it can only be understood as rotation relative to some sort of absolute space. In the case of GTR, this is indeed the natural way to understand such a model: the rotation is best understood as rotation relative to a ‘background’ spacetime that is identical to the Minkowski spacetime of STR, only ‘curved’ by the presence of matter in the region of the star.