Theory of relativity is a framework within physics that fundamentally describes the relationship between space and time, and how gravity affects the structure of the universe. It comprises multiple theories, including one addressing motion at constant velocities and another addressing acceleration and gravitation. Conceptually, the theory posits that space and time are interwoven into a single four-dimensional manifold called spacetime, and that the presence of mass and energy causes curvature within this manifold. This curvature is what is perceived as gravitational force, meaning that gravity is not a force transmitting across space, but rather a manifestation of the distortion of spacetime itself. A central implication of the theory is the equivalence of mass and energy, establishing that mass can be converted into a massive amount of energy, and vice versa.