Difference between revisions 147178448 and 147178449 on dewiki

{{string-theory}}
{{see|string theory}}

'''Superstring theory''' is an attempt to explain all of the [[Elementary particle|particles]] and [[fundamental force]]s of nature in one theory by modeling them as vibrations of tiny [[supersymmetry|supersymmetric]] strings. It is considered one of the most promising candidate theories of [[quantum gravity]]. 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]].

== Background ==

The deepest problem in [[theoretical physics]] is harmonizing the theory of [[general relativity]], which describes gravitation and applies to large-scale structures ([[star]]s, [[galaxies, ]], [[super cluster]]s), 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. Physicists have developed mathematical techniques ([[renormalization]]) to eliminate these infinities which work for three of the four fundamental forces - electromagnetic, – [[Electromagnetic force|electromagnetic]], [[Strong interaction|strong nuclear]] and [[Weak interaction|weak nuclear]] forces - but not for [[gravity]]. The development of a [[quantum theory of gravity]] must therefore come about by different means than those used for the other forces.

=== Basic idea ===⏎
⏎
The basic idea is that the fundamental constituents of reality are strings of the [[Planck units|Planck length]] (about 10<sup>&minus;35</sup> m) which vibrate at [[resonance|resonant]] frequencies. Every string in theory has a unique resonance, or harmonic. Different harmonics determine different fundamental forces. The tension in a string is   on the order of the [[Planck force]] (10<sup>44</sup> [[newton]]s). The [[graviton]] (the proposed messenger particle of the gravitational force), for example, is predicted by the theory to be a string with wave amplitude zero. Another key insight provided by the theory is that no measurable differences can be detected between strings that wrap around dimensions smaller than themselves and those that move along larger dimensions (i.e., effects in a dimension of size R equal those whose size is 1/R). Singularities are avoided because the observed consequences of "[[Big Crunch|big crunch]]es" never reach zero size.  In fact, should the universe begin a "big crunch" sort of process, string theory dictates that the universe could never be smaller than the size of a string, at which point it would actually begin expanding.

== Extra dimensions==
:''See also: Why does consistency require [[Why 10 dimensions|10 dimensions]]?''
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