A theory which postulates that the fundamental ingredients of the universe are tiny strings of matter (on the tiny scale of the Planck Length of around 10-35 metres) which vibrate in a space-time of ten dimensions. It is considered one of the most promising of the quantum gravity theories which hope to unite or unify quantum theory and the General Theory of Relativity, and apply to both large-scale structures and structures on the atomic scale. Superstring theory (short for supersymmetric string theory) is a refinement of the more general theory of strings.