Theoretical physics is a branch of physics that uses mathematical models and abstractions of physical objects and systems to explain and predict natural phenomena. It is, in the broadest sense, the attempt to say why things happen the way they do, not merely to record that they do. This is in contrast to experimental physics, which tests and refines those explanations through direct measurement and observation. In practice, the two feed each other constantly: a theoretical prediction suggests an experiment, and an unexpected experimental result sends theorists back to the drawing board.