string theory

String theory is a type of physics theory developed in the latter half of the twentieth century that has the concept of an underlying structure consisting of objects termed strings whose shapes, vibrations, oscillations, and interactions form the particles of the standard model as well as gravity, potentially relating everything we know about physics. The term string is used because the objects have length rather than being point-like objects as we imagine particles to be. The strings may be in loops, and various physical characteristics are modeled by their vibrations. While these theories can be made to explain a lot, many variants have been proposed without exhausting the possibilities. Tests of their validity are lacking, so the theories are explored but remain speculative. Superstring theory is a type of variant that includes supersymmetry.