M-theory is a theory in physics that unifies all consistent versions of superstring theory. The existence of such a theory was first conjectured by Edward Witten at the string theory conference at the University of Southern California in the summer of 1995. Witten's announcement initiated a flurry of research activity known as the second superstring revolution.
Prior to Witten's announcement, string theorists had identified five different versions of superstring theory. Although these theories appeared at first to be very different, work by a number of different physicists including Ashoke Sen, Chris Hull, Paul Townsend, and Michael Duff showed that the theories were related in intricate and nontrivial ways. In particular, physicists found that the apparently distinct theories were identified by mathematical transformations called S-duality and T-duality. Witten's conjecture was based in part on the existence of these dualities and in part on the relationship of the string theories to a gravitational theory called eleven-dimensional supergravity.
Although a complete formulation of M-theory is not known, the theory should describe two- and five-dimensional objects called branes and should be approximated by eleven-dimensional supergravity at low energies. Modern attempts to formulate M-theory are typically based on matrix theory or the AdS/CFT correspondence. According to Witten, the M in M-theory can stand for "magic", "mystery", or "matrix" according to taste, and the true meaning of the title should be decided when a more fundamental formulation of the theory is known.
Investigations of the mathematical structure of M-theory have spawned a number of important theoretical results in physics and mathematics. More speculatively, M-theory may provide a framework for developing a unified theory of all of the fundamental forces of nature. Attempts to connect M-theory to experiment typically focus on compactifying its extra dimensions to construct approximate models of our four-dimensional world.
Prior to Witten's announcement, string theorists had identified five different versions of superstring theory. Although these theories appeared at first to be very different, work by a number of different physicists including Ashoke Sen, Chris Hull, Paul Townsend, and Michael Duff showed that the theories were related in intricate and nontrivial ways. In particular, physicists found that the apparently distinct theories were identified by mathematical transformations called S-duality and T-duality. Witten's conjecture was based in part on the existence of these dualities and in part on the relationship of the string theories to a gravitational theory called eleven-dimensional supergravity.
Although a complete formulation of M-theory is not known, the theory should describe two- and five-dimensional objects called branes and should be approximated by eleven-dimensional supergravity at low energies. Modern attempts to formulate M-theory are typically based on matrix theory or the AdS/CFT correspondence. According to Witten, the M in M-theory can stand for "magic", "mystery", or "matrix" according to taste, and the true meaning of the title should be decided when a more fundamental formulation of the theory is known.
Investigations of the mathematical structure of M-theory have spawned a number of important theoretical results in physics and mathematics. More speculatively, M-theory may provide a framework for developing a unified theory of all of the fundamental forces of nature. Attempts to connect M-theory to experiment typically focus on compactifying its extra dimensions to construct approximate models of our four-dimensional world.
