M-Theory

CORE DEFINITION

M-theory is a theory in physics that unifies various compatible forms of superstring theory. It was first proposed by American mathematical physicist Edward Witten in the spring of 1995 at a string theory conference held at the University of Southern California. Witten's talk sparked a surge of research in string theory, known as the second superstring revolution. Before Witten's talk, string theorists had identified five different superstring theories. Although these theories seemed very different, research by several physicists indicated that they had subtle and significant relationships. In particular, physicists found that these seemingly different theories could actually be unified through two mathematical transformations called S-duality and T-duality. Witten's conjecture was based partly on the existence of these dualities and partly on the relationship between string theory and 11-dimensional supergravity. Although a complete formulation of M-theory has not yet been found, the theory is expected to describe two- and five-dimensional objects called branes, and should also describe 11-dimensional supergravity at low energies. Current attempts to formulate M-theory are generally based on matrix theory or the AdS/CFT correspondence.