Editing String theory (section)

{{Short description|Theory of subatomic structure}}
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{{Seeintro|Introduction to M-theory}}
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{{String theory}}

In [[physics]], '''string theory''' is a [[Mathematical theory|theoretical framework]] in which the [[Point particle|point-like particles]] of [[particle physics]] are replaced by [[Dimension (mathematics and physics)|one-dimensional]] objects called [[String (physics)|strings]]. String theory describes how these strings propagate through space and interact with each other. On distance scales larger than the string scale, a string acts like a particle, with its [[mass]], [[charge (physics)|charge]], and other properties determined by the [[vibration]]al state of the string. In string theory, one of the many vibrational states of the string corresponds to the [[graviton]], a [[quantum mechanics|quantum mechanical]] particle that carries the [[gravity|gravitational force]]. Thus, string theory is a theory of [[quantum gravity]].

String theory is a broad and varied subject that attempts to address a number of deep questions of [[fundamental physics]]. String theory has contributed a number of advances to [[mathematical physics]], which have been applied to a variety of problems in [[black hole]] physics, early universe [[Physical cosmology|cosmology]], [[nuclear physics]], and [[condensed matter physics]], and it has stimulated a number of major developments in [[pure mathematics]]. Because string theory potentially provides a unified description of gravity and particle physics, it is a candidate for a [[theory of everything]], a self-contained [[mathematical model]] that describes all [[Fundamental interaction|fundamental force]]s and forms of [[matter]]. Despite much work on these problems, it is not known to what extent string theory describes the real world or how much freedom the theory allows in the choice of its details.

String theory was first studied in the late 1960s as a theory of the [[strong nuclear force]], before being abandoned in favor of [[quantum chromodynamics]]. Subsequently, it was realized that the very properties that made string theory unsuitable as a theory of nuclear physics made it a promising candidate for a quantum theory of gravity. The earliest version of string theory, [[bosonic string theory]], incorporated only the class of [[particle]]s known as [[boson]]s. It later developed into [[superstring theory]], which posits a connection called [[supersymmetry]] between bosons and the class of particles called [[fermion]]s. Five consistent versions of superstring theory were developed before it was conjectured in the mid-1990s that they were all different limiting cases of a single theory in eleven dimensions known as [[M-theory]]. In late 1997, theorists discovered an important relationship called the [[anti-de Sitter/conformal field theory correspondence]] (AdS/CFT correspondence), which relates string theory to another type of physical theory called a [[quantum field theory]].

One of the challenges of string theory is that the full theory does not have a satisfactory definition in all circumstances. Another issue is that the theory is thought to describe an enormous [[String theory landscape|landscape]] of possible [[universe]]s, which has complicated efforts to develop theories of particle physics based on string theory. These issues have led some in the community to criticize these approaches to physics, and to question the value of continued research on string theory unification.