 Gravity is the dominant interaction at large length scales. General relativity introduced a new way of representing gravity: rather than describing gravity as a force deflecting bodies from inertial motion, bodies free from non-gravitational forces move along the analog of straight lines, called geodesics, through a curved spacetime  geometry.[3]  The spacetime curvature is related to the distribution of energy and matter through GR’s fundamental equations (Einstein’s field equations, EFE). The dynamics of the theory are non-linear: matter curves spacetime, and the curvature of spacetime determines how matter moves; and gravitational waves interact with each other gravitationally, and act as gravitational sources. The theory also replaces the single gravitational potential, and associated field equation, of Newton’s theory, with a set of 10 coupled, non-linear equations for ten independent  potentials.[4]  This complexity is an obstacle to understanding the general features of solutions to EFE, and to finding exact solutions to describe specific physical situations. Most exact solutions have been found based on strong idealizations, introduced to simplify the mathematics.