Edward Witten in the context of String theory

In physics, M-theory is a theory that unifies all consistent versions of superstring theory. Edward Witten first conjectured the existence of such a theory at a string theory conference at the University of Southern California in 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 versions of superstring theory. Although these theories initially appeared to be very different, work by many physicists showed that the theories were related in intricate and nontrivial ways. Physicists found that apparently distinct theories could be unified 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 field theory called eleven-dimensional supergravity.

Although a complete formulation of M-theory is not known, such a formulation 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 should stand for "magic", "mystery" or "membrane" (according to one's taste), and the true meaning of the title should be decided when a more fundamental formulation of the theory is known.

Jonathan Anders Bagger (born August 7, 1955) is an American theoretical physicist, specializing in high energy physics and string theory and known for the Bagger–Lambert–Gustavsson action.

Bagger received his bachelor's degree in 1977 from Dartmouth College. He spent the academic year 1977–1978 at the University of Cambridge as a Churchill Scholar. In 1978 he became a graduate student in physics at Princeton University, where he received his PhD in 1983. His doctoral thesis Matter Couplings in Supergravity Theories was supervised by Edward Witten. He was a postdoc from 1983 to 1986 at the Stanford Linear Accelerator Center. He was from 1986 to 1989 an associate professor at Harvard University. At Johns Hopkins University he became in 1989 a full professor, holding a professorial chair there until 2014. In 2014 he was appointed director of TRIUMF, Canada's national laboratory for particle and nuclear physics.

In theoretical physics, S-duality (short for strong–weak duality, or Sen duality) is an equivalence of two physical theories, which may be either quantum field theories or string theories. S-duality is useful for doing calculations in theoretical physics because it relates a theory in which calculations are difficult to a theory in which they are easier.

In quantum field theory, S-duality generalizes a well established fact from classical electrodynamics, namely the invariance of Maxwell's equations under the interchange of electric and magnetic fields. One of the earliest known examples of S-duality in quantum field theory is Montonen–Olive duality which relates two versions of a quantum field theory called N = 4 supersymmetric Yang–Mills theory. Recent work of Anton Kapustin and Edward Witten suggests that Montonen–Olive duality is closely related to a research program in mathematics called the geometric Langlands program. Another realization of S-duality in quantum field theory is Seiberg duality, which relates two versions of a theory called N=1 supersymmetric Yang–Mills theory.