No well-defined current physical theory claims to model all nature; each intentionally neglects some effects. Roughly, general relativity is a model of nature, especially of gravity, that neglects quantum effect. Its central assumption is that space, time, and gravity are all aspects of a single entity, called spacetime, which is modelled by a 4-dimensional Lorentzian manifold. It analyzes spacetime, electromagnetism, matter and their mutual influences.