Superstring theory is an attempt to explain all of the particles and fundamental forces of nature in one theory by modeling them as vibrations of tiny 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. In particle physics, an elementary particle or fundamental particle is a particle not known to have substructure; that is, it is not made up of smaller particles. ... A fundamental interaction is a mechanism by which particles interact with each other, and which cannot be explained by another more fundamental interaction. ... This article or section is in need of attention from an expert on the subject. ... This article does not cite any references or sources. ... Bosonic string theory is the original version of string theory, developed in the late 1960s. ... Interaction in the subatomic world: world lines of pointlike particles in the Standard Model or a world sheet swept up by closed strings in string theory String theory is a model of fundamental physics whose building blocks are one-dimensional extended objects called strings, rather than the zero-dimensional point... Fermions, named after Enrico Fermi, are particles which form totally-antisymmetric composite quantum states. ... This article or section is in need of attention from an expert on the subject. ...

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. Theoretical physics employs mathematical models and abstractions of physics, as opposed to experimental processes, in an attempt to understand nature. ... For a less technical and generally accessible introduction to the topic, see Introduction to general relativity. ... Fig. ... A fundamental interaction is a mechanism by which particles interact with each other, and which cannot be explained by another more fundamental interaction. ...

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, strong nuclear and 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. Quantum field theory (QFT) is the quantum theory of fields. ... Figure 1. ...

The basic idea is that the fundamental constituents of reality are strings of the Planck length (about 10⁻³⁵ m) which vibrate at 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 (10⁴⁴ newtons). 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 crunches" 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. In physics, Planck units are physical units of measurement defined exclusively in terms of the five universal physical constants shown in the table below in such a manner that all of these physical constants take on the numerical value of one when expressed in terms of these units. ... This article is about resonance in physics. ... Planck Force A derived Planck unit equated to the Planck Energy (also derived) divided by the Planck length. ... For other uses, see Newton (disambiguation). ... In physics, the graviton is mainly still considered to be a hypothetical elementary particle that mediates the force of gravity in the framework of quantum field theory. ... This article is about the cosmological theory. ...

Extra dimensions

See also: Why does consistency require 10 dimensions?

Our physical space is observed to have only three large dimensions — and taken together with time as the fourth dimension — a physical theory must take this into account. However, nothing prevents a theory from including more than 4 dimensions, per se. In the case of string theory, consistency requires spacetime to have 10, 11 or 26 dimensions. The conflict between observation and theory is resolved by making the unobserved dimensions compactified. In our personal human experiences, we seem to exist in a universe with three spatial dimensions. ... According to comedian Steven Wright, physical space is the thing that keeps everything from happening in the same place. ... 2-dimensional renderings (ie. ... Interaction in the subatomic world: world lines of pointlike particles in the Standard Model or a world sheet swept up by closed strings in string theory String theory is a model of fundamental physics whose building blocks are one-dimensional extended objects called strings, rather than the zero-dimensional point... Look up Consistency in Wiktionary, the free dictionary. ... For other uses of this term, see Spacetime (disambiguation). ... In string theory, a model used in theoretical physics, a compact dimension is curled up in itself and very small (Planck length). ...

Our minds have difficulty visualizing higher dimensions because we can only move in three spatial dimensions. One way of dealing with this limitation is not to try to visualize higher dimensions at all, but just to think of them as extra numbers in the equations that describe the way the world works. This opens the question of whether these 'extra numbers' can be investigated directly in any experiment (which must show different results in 1, 2, or 2+1 dimensions to a human scientist). This, in turn, raises the question of whether models that rely on such abstract modeling (and potentially impossibly huge experimental apparatus) can be considered 'scientific.' Six-dimensional Calabi-Yau shapes can account for the additional dimensions required by superstring theory. In mathematics, a Calabi-Yau manifold is a compact K hler manifold with a vanishing first Chern class. ...

Superstring theory is not the first theory to propose extra spatial dimensions; see Kaluza-Klein theory. Modern string theory relies on the mathematics of folds, knots, and topology, which was largely developed after Kaluza and Klein, and has made physical theories relying on extra dimensions much more credible. In physics, Kaluza-Klein theory (or KK theory, for short) is a model that seeks to unify the two fundamental forces of gravitation and electromagnetism. ... A Möbius strip, an object with only one surface and one edge; such shapes are an object of study in topology. ...

Unsolved problems in physics: Is string theory, superstring theory, or M-theory, or some other variant on this theme, a step on the road to a "theory of everything," or just a blind alley?

Image File history File links No higher resolution available. ... This is a list of some of the unsolved problems in physics. ... Interaction in the subatomic world: world lines of pointlike particles in the Standard Model or a world sheet swept up by closed strings in string theory String theory is a model of fundamental physics whose building blocks are one-dimensional extended objects called strings, rather than the zero-dimensional point... M-theory is a solution proposed for the unknown theory of everything which would combine all five superstring theories and 11-dimensional supergravity together. ... This article or section is in need of attention from an expert on the subject. ...

Number of superstring theories

Theoretical physicists were troubled by the existence of five separate superstring theories. This has been solved by the second superstring revolution in the 1990s during which the five superstring theories were discovered to be different limits of a single underlying theory: M-theory. The second superstring revolution refers to the intense wave of breakthroughs in string theory that took place approximately between 1994 and 1997. ... For the band, see 1990s (band). ... M-theory is a solution proposed for the unknown theory of everything which would combine all five superstring theories and 11-dimensional supergravity together. ...

The five consistent superstring theories are: In particle physics, bosons, named after Satyendra Nath Bose, are particles having integer spin. ... In particle physics, fermions are particles with half-integer spin, such as protons and electrons. ... Thousands of particles explode from the collision point of two relativistic (100 GeV per nucleon) gold ions in the STAR detector of the Relativistic Heavy Ion Collider. ... This article or section is in need of attention from an expert on the subject. ... A tachyon (from the Greek (takhús), meaning swift, fast) is any hypothetical particle that travels at superluminal velocity. ... This article or section is in need of attention from an expert on the subject. ... A tachyon (from the Greek (takhús), meaning swift, fast) is any hypothetical particle that travels at superluminal velocity. ... In mathematics, the orthogonal group of degree n over a field F (written as O(n,F)) is the group of n-by-n orthogonal matrices with entries from F, with the group operation that of matrix multiplication. ... This article or section is in need of attention from an expert on the subject. ... A tachyon (from the Greek (takhús), meaning swift, fast) is any hypothetical particle that travels at superluminal velocity. ... In particle physics, fermions are particles with half-integer spin, such as protons and electrons. ... This article or section is in need of attention from an expert on the subject. ... A tachyon (from the Greek (takhús), meaning swift, fast) is any hypothetical particle that travels at superluminal velocity. ... In particle physics, fermions are particles with half-integer spin, such as protons and electrons. ... This article or section is in need of attention from an expert on the subject. ... A tachyon (from the Greek (takhús), meaning swift, fast) is any hypothetical particle that travels at superluminal velocity. ... In physics, a heterotic string is a peculiar mixture (or hybrid) of the bosonic string and the superstring (the adjective heterotic comes from the Greek word heterosis). ... In mathematics, the orthogonal group of degree n over a field F (written as O(n,F)) is the group of n-by-n orthogonal matrices with entries from F, with the group operation that of matrix multiplication. ... This article or section is in need of attention from an expert on the subject. ... A tachyon (from the Greek (takhús), meaning swift, fast) is any hypothetical particle that travels at superluminal velocity. ... In physics, a heterotic string is a peculiar mixture (or hybrid) of the bosonic string and the superstring (the adjective heterotic comes from the Greek word heterosis). ... Graph of E8 Gosset polytope, 42,1 Coxeter-Dynkin diagram: . It features superscript or subscript characters that are substituted or omitted because of technical limitations. ...

• The type I string has one supersymmetry in the ten-dimensional sense (16 supercharges). This theory is special in the sense that it is based on unoriented open and closed strings, while the rest are based on oriented closed strings.
• The type II string theories have two supersymmetries in the ten-dimensional sense (32 supercharges). There are actually two kinds of type II strings called type IIA and type IIB. They differ mainly in the fact that the IIA theory is non-chiral (parity conserving) while the IIB theory is chiral (parity violating).
• The heterotic string theories are based on a peculiar hybrid of a type I superstring and a bosonic string. There are two kinds of heterotic strings differing in their ten-dimensional gauge groups: the heterotic E₈×E₈ string and the heterotic SO(32) string. (The name heterotic SO(32) is slightly inaccurate since among the SO(32) Lie groups, string theory singles out a quotient Spin(32)/Z₂ that is not equivalent to SO(32).)

Chiral gauge theories can be inconsistent due to anomalies. This happens when certain one-loop Feynman diagrams cause a quantum mechanical breakdown of the gauge symmetry. Having anomalies cancel puts a severe constraint on possible superstring theories. In theoretical physics, type I string theory is one of five consistent supersymmetric string theories in ten dimensions. ... An open string is a one-dimensional fundamental object in string theory that has two end-points, and therefore is topologically equivalent to a line interval. ... A closed string is a one-dimensional fundamental object in string theory that has no end-points, and therefore is topologically equivalent to a circle. ... In theoretical physics, type II string theory is a unified term that includes both type IIA strings and type IIB strings. ... A phenomenon is said to be chiral if it is not identical to its mirror image (see Chirality (mathematics)). The spin of a particle may be used to define a handedness for that particle. ... In physics, a heterotic string is a peculiar mixture (or hybrid) of the bosonic string and the superstring (the adjective heterotic comes from the Greek word heterosis). ... Gauge theories are a class of physical theories based on the idea that symmetry transformations can be performed locally as well as globally. ... Graph of E8 Gosset polytope, 42,1 Coxeter-Dynkin diagram: . It features superscript or subscript characters that are substituted or omitted because of technical limitations. ... In mathematics, the orthogonal group of degree n over a field F (written as O(n,F)) is the group of n-by-n orthogonal matrices with entries from F, with the group operation that of matrix multiplication. ... In mathematics, a Lie group, named after Norwegian mathematician Sophus Lie (IPA pronunciation: , sounds like Lee), is a group which is also a differentiable manifold, with the property that the group operations are compatible with the smooth structure. ... In physics, gauge theories are a class of physical theories based on the idea that symmetry transformations can be performed locally as well as globally. ... In physics, an anomaly is a classical symmetry — a symmetry of the Lagrangian — that is broken in quantum field theories. ... In this Feynman diagram, an electron and positron annihilate and become a quark-antiquark pair. ...

Integrating general relativity and quantum mechanics

General relativity typically deals with situations involving large mass objects in fairly large regions of spacetime whereas quantum mechanics is generally reserved for scenarios at the atomic scale (small spacetime regions). The two are very rarely used together, and the most common case in which they are combined is in the study of black holes. Having "peak density", or the maximum amount of matter possible in a space, and very small area, the two must be used in synchrony in order to predict conditions in such places; yet, when used together, the equations fall apart, spitting out impossible answers, such as imaginary distances and less than one dimension. For a less technical and generally accessible introduction to the topic, see Introduction to general relativity. ... For other uses of this term, see Spacetime (disambiguation). ... Fig. ... For other uses, see Black hole (disambiguation). ...

The major problem with their congruence is that, at sub-Planck (an extremely small unit of length) lengths, general relativity predicts a smooth, flowing surface, while quantum mechanics predicts a random, warped surface, neither of which are anywhere near compatible. Superstring theory resolves this issue, replacing the classical idea of point particles with loops. These loops have an average diameter of the Planck length, with extremely small variances, which completely ignores the quantum mechanical predictions of sub-Planck length dimensional warping, there being no matter that is of sub-Planck length.

See also

• AdS/CFT
• Grand unification theory
• List of string theory topics
• M-theory
• Quantum gravity
• String theory

In physics, the AdS/CFT correspondence is the equivalence between a string theory or supergravity defined on some sort of Anti de Sitter space and a conformal field theory defined on its boundary whose dimension is lower by one. ... It has been suggested that this article or section be merged into Unified field theory. ... This is a list of string theory topics, by Wikipedia page. ... M-theory is a solution proposed for the unknown theory of everything which would combine all five superstring theories and 11-dimensional supergravity together. ... This article does not cite any references or sources. ... Interaction in the subatomic world: world lines of pointlike particles in the Standard Model or a world sheet swept up by closed strings in string theory String theory is a model of fundamental physics whose building blocks are one-dimensional extended objects called strings, rather than the zero-dimensional point...

References

• For further reference see the list at string theory.