![]() One of the vibrational states of a string gives rise to the graviton, a quantum mechanical particle that carries gravitational force. In this way, all of the different elementary particles may be viewed as vibrating strings. On distance scales larger than the string scale, a string will look just like an ordinary particle, with its mass, charge, and other properties determined by the vibrational state of the string. In a given version of string theory, there is only one kind of string, which may look like a small loop or segment of ordinary string, and it can vibrate in different ways. String theory describes how strings propagate through space and interact with each other. In string theory, the point-like particles of particle physics are replaced by one-dimensional objects called strings. String theory is a theoretical framework that attempts to reconcile gravity and quantum mechanics. ![]() A quantum theory of gravity is needed in order to reconcile general relativity with the principles of quantum mechanics, but difficulties arise when one attempts to apply the usual prescriptions of quantum theory to the force of gravity. However, nongravitational forces are described within the framework of quantum mechanics, a radically different formalism for describing physical phenomena based on probability. The current understanding of gravity is based on Albert Einstein's general theory of relativity, which is formulated within the framework of classical physics. One of the deepest problems in modern physics is the problem of quantum gravity. The fundamental objects of string theory are open and closed strings. Attempts to connect M-theory to experiment typically focus on compactifying its extra dimensions to construct candidate models of the four-dimensional world, although so far none has been verified to give rise to physics as observed in high-energy physics experiments.īackground Quantum gravity and strings More speculatively, M-theory may provide a framework for developing a unified theory of all of the fundamental forces of nature. Investigations of the mathematical structure of M-theory have spawned important theoretical results in physics and mathematics. According to Witten, M should stand for "magic", "mystery" or "membrane" according to taste, and the true meaning of the title should be decided when a more fundamental formulation of the theory is known. ![]() Modern attempts to formulate M-theory are typically based on matrix theory or the AdS/CFT correspondence. 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.Īlthough 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. Physicists found that apparently distinct theories could be unified by mathematical transformations called S-duality and T-duality. Although these theories initially appeared to be very different, work by many physicists showed that the theories were related in intricate and nontrivial ways. Prior to Witten's announcement, string theorists had identified five versions of superstring theory. ![]() Witten's announcement initiated a flurry of research activity known as the second superstring revolution. Edward Witten first conjectured the existence of such a theory at a string theory conference at the University of Southern California in 1995 ( M-Theory - Edward Witten (1995)). M-theory is a theory in physics that unifies all consistent versions of superstring theory.
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