**String theory** is an active research framework in particle physics that attempts to reconcile quantum mechanics and general relativity. It is a contender for a theory of everything (TOE), a self-contained mathematical model that describes all fundamental forces and forms of matter. String theory posits that the elementary particles (i.e., electrons and quarks) within an atom are not 0-dimensional objects, but rather 1-dimensional oscillating lines ("strings").

The earliest string model, the bosonic string, incorporated only bosons, although this view developed to the superstring theory, which posits that a connection (a "supersymmetry") exists between bosons and fermions. String theories also require the existence of several extra dimensions to the universe that have been compactified into extremely small scales, in addition to the four known spacetime dimensions.

The theory has its origins in an effort to understand the strong force, the dual resonance model (1969). Subsequent to this, five superstring theories were developed that incorporated fermions and possessed other properties necessary for a theory of everything. Since the mid-1990s, in particular due to insights from dualities shown to relate the five theories, an eleven-dimensional theory called M-theory is believed to encompass all of the previously distinct superstring theories.

Many theoretical physicists (among them Stephen Hawking, Edward Witten, Juan Maldacena and Leonard Susskind) believe that string theory is a step towards the correct fundamental description of nature. This is because string theory allows for the consistent combination of quantum field theory and general relativity, agrees with general insights in quantum gravity (such as the holographic principle and black hole thermodynamics), and because it has passed many non-trivial checks of its internal consistency. According to Hawking in particular, "M-theory is the *only* candidate for a complete theory of the universe." Nevertheless, other physicists, such as Feynman and Glashow, have criticized string theory for not providing novel experimental predictions at accessible energy scales.

Read more about String Theory: Overview, Basic Properties, Testability and Experimental Predictions, Gauge/gravity Duality, History, Criticisms

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### Famous quotes containing the words theory and/or string:

“Psychotherapy—The *theory* that the patient will probably get well anyway, and is certainly a damned ijjit.”

—H.L. (Henry Lewis)

“A culture may be conceived as a network of beliefs and purposes in which any *string* in the net pulls and is pulled by the others, thus perpetually changing the configuration of the whole. If the cultural element called morals takes on a new shape, we must ask what other strings have pulled it out of line. It cannot be one solitary *string*, nor even the strings nearby, for the network is three-dimensional at least.”

—Jacques Barzun (b. 1907)