A Grand Unified Theory (GUT) is a model in particle physics in which at high energy, the three gauge interactions of the Standard Model which define the electromagnetic, weak, and strong interactions, are merged into one single interaction characterized by one larger gauge symmetry and thus one unified coupling constant. During the grand unification epoch, the gauge force separated from the gravitational force. Models that do not unify all interactions using one simple Lie group as the gauge symmetry, but do so using semisimple groups, can exhibit similar properties and are sometimes referred to as Grand Unified Theories as well. Unifying gravity with the other three interactions would provide a theory of everything (TOE), rather than a GUT. Nevertheless, GUTs are often seen as an intermediate step towards a TOE. History Motivation Unification of matter particles Schematic representation of fermions and bosons in SU(5) GUT showing 5+10 split in the multiplets. SU(5) If
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Relationship between string theory and quantum field theoryMany first principles in quantum field theory are explained, or get further insight, in string theory: Note: formally, gauge symmetries in string theory are (at least in most cases) a result of the existence of a global symmetry together with the profound gauge symmetry of string theory, which is the symmetry of the worldsheet under a local change of coordinates and scales.Attempt at a unified field theorySuperstring theory'Superstring theory' is a shorthand for supersymmetric string theory because unlike bosonic string theory, it is the version of string theory that incorporates fermions and supersymmetry. Since the second superstring revolution the five superstring theories are regarded as different limits of a single theory tentatively called M-theory, or simply string theory. Background The deepest problem in theoretical physics is harmonizing the theory of general relativity, which describes gravitation and applies to large-scale structures (stars, galaxies, super clusters), with quantum mechanics, which describes the other three fundamental forces acting on the atomic scale. The development of a quantum field theory of a force invariably results in infinite (and therefore useless) probabilities. Evidence Superstring theory is based on supersymmetry. Extra dimensions See also: Why does consistency require 10 dimensions? Number of superstring theories The five superstring interactions
Relativity and quantum mechanicsJohann Wolfgang von GoetheAfter returning from a tour of Italy in 1788, his first major scientific work, the Metamorphosis of Plants, was published. In 1791 he was made managing director of the theatre at Weimar, and in 1794 he began a friendship with the dramatist, historian, and philosopher Friedrich Schiller, whose plays he premiered until Schiller's death in 1805. During this period Goethe published his second novel, Wilhelm Meister's Apprenticeship, the verse epic Hermann and Dorothea, and, in 1808, the first part of his most celebrated drama, Faust. Arthur Schopenhauer cited Wilhelm Meister's Apprenticeship as one of the four greatest novels ever written, along with Tristram Shandy, La Nouvelle Heloïse, and Don Quixote, and Ralph Waldo Emerson selected Goethe as one of six "representative men" in his work of the same name, along with Plato, Napoleon, and William Shakespeare. Biography Early life Goethe's birthplace in Frankfurt, Germany (Großer Hirschgraben) Legal career Italy
Interpretations of quantum mechanicsAn interpretation of quantum mechanics is a set of statements which attempt to explain how quantum mechanics informs our understanding of nature. Although quantum mechanics has held up to rigorous and thorough experimental testing, many of these experiments are open to different interpretations. There exist a number of contending schools of thought, differing over whether quantum mechanics can be understood to be deterministic, which elements of quantum mechanics can be considered "real", and other matters. This question is of special interest to philosophers of physics, as physicists continue to show a strong interest in the subject. History of interpretations Main quantum mechanics interpreters An early interpretation has acquired the label Copenhagen interpretation, and is often used. Nature of interpretation An interpretation of quantum mechanics is a conceptual or argumentative way of relating between: Two qualities vary among interpretations: Concerns of Einstein
Quantum mechanics and classical physicsM-theoryM-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. Background Quantum gravity and strings One of the deepest problems in modern physics is the problem of quantum gravity. Number of dimensions In everyday life, there are three familiar dimensions of space (up/down, left/right, and forward/backward), and there is one dimension of time (later/earlier). Despite the obvious relevance of four-dimensional spacetime for describing the physical world, there are several reasons why physicists often consider theories in other dimensions. Dualities Main articles: S-duality and T-duality A diagram of string theory dualities. and winding number in the dual description. .