A string is the fundamental object of study in a branch of theoretical physics called string theory. A string is an object with a one-dimensional spatial extent, unlike an elementary particle which is zero-dimensional. String theory is a model of fundamental physics whose building blocks are one-dimensional extended objects (strings) rather than the zero-dimensional points (particles) that are the basis of the Standard Model of particle physics. ... Bosonic string theory is the original version of string theory, developed in the late 1960s. ... 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. ... In theoretical physics, type I string theory is one of five consistent supersymmetric string theories in ten dimensions. ... In theoretical physics, type II string theory is a unified term that includes both type IIA strings and type IIB strings. ... 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). ... M-theory is a solution proposed for the unknown theory of everything which would combine all five superstring theories and 11-dimensional supergravity together. ... String field theory is a proposal to define string theory in such a way that the background independence is respected. ... Branes are objects in M-theory and its offshoot, brane cosmology. ... Quantum field theory (QFT) is the application of quantum mechanics to fields. ... Gauge theories are a class of physical theories based on the idea that symmetry transformations can be performed locally as well as globally. ... A conformal field theory is a quantum field theory (or statistical mechanics model) that is invariant under the conformal group. ... Topological quantum field theory in theoretical physics provides an example of background-independent quantum theory, but with no local degrees of freedom, and only finitely many degrees of freedom globally. ... This article needs to be cleaned up to conform to a higher standard of quality. ... In theoretical physics, a supergravity theory is a field theory combining supersymmetry and general relativity. ... General relativity (GR) is the geometrical theory of gravitation published by Albert Einstein in 1915. ... // Headline text Quantum gravity is the field of theoretical physics attempting to unify the theory of quantum mechanics, which describes three of the fundamental forces of nature, with general relativity, the theory of the fourth fundamental force: gravity. ... This is a list of string theory topics, by Wikipedia page. ... Theoretical physics is physics that employs mathematical models and abstractions rather than experimental processes. ... String theory is a model of fundamental physics whose building blocks are one-dimensional extended objects (strings) rather than the zero-dimensional points (particles) that are the basis of the Standard Model of particle physics. ... In particle physics, an elementary particle is a particle of which other, larger particles are composed. ...

The strings in string theory are tiny objects with dimensions close to the Planck length (1.6×10^-33 cm) [1]. On much larger scales, such as the scales visible in physics laboratories, such objects would look very similiar to zero-dimensional point particles. According to string theory, the various elementary particles in the standard model of quantum field theory, correspond to different vibrational modes of tiny fundamental strings. 4The Planck length is the natural unit of length, denoted by . ... The Standard Model of Fundamental Particles and Interactions The Standard Model of particle physics is a theory which describes the strong, weak, and electromagnetic fundamental forces, as well as the fundamental particles that make up all matter. ... Quantum field theory (QFT) is the application of quantum mechanics to fields. ...

Propogating in spacetime, strings sweep out a two-dimensional surface, called a worldsheet, analogous to the one-dimensional worldline traced out by a point particle. World line of the orbit of the Earth depicted in two spatial dimensions X and Y (the plane of the Earth orbit) and a time dimension, usually put as the vertical axis. ... An open surface with X-, Y-, and Z-contours shown. ... A world line of an object or person is the sequence of events labeled with time and place, that marks the history of the object or person. ...

Types of strings

Closed and open strings

Strings can be either open or closed. A closed string is a string that has no end-points, and therefore is topologically equivalent to a circle. An open string, on the otherhand, has two end-points and is topologically equivalent to a line interval. This word should not be confused with homomorphism. ... In Euclidean geometry, a circle is the set of all points at a fixed distance, called the radius, from a fixed point, called the centre (center). ...

Not all string theories contain both open and closed strings. However, any theory which contains open strings must also contain closed strings as interactions between open strings can always result in closed strings.

The oldest superstring theory containing open strings was type I string theory. However, the developments in string theory in the 1990s have shown that the open strings should always be thought of as ending on a new type of objects called the D-branes, and the spectrum of possibilities for open strings has increased a lot. 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. ... In theoretical physics, type I string theory is one of five consistent supersymmetric string theories in ten dimensions. ... In theoretical physics, D-branes are a special class of p-branes, named for the physicist Johann Dirichlet. ...

Open and closed strings both have their own characteristic vibrational patterns. One of the vibratation modes of a closed string can be identified the graviton. In certain string theories the lowest-energy vibration of an open string is a tachyon and can undergo tachyon condensation. One of the other vibrational patterns of an open string exhibits properties similiar to a photon and so on. In physics, the graviton is a hypothetical elementary particle that transmits the force of gravity in most quantum gravity systems. ... A tachyon (from the Greek ταχύς takhús, meaning swift) is any hypothetical particle that travels at superluminal velocity. ... In physics, tachyon condensation is a process in which a tachyonic field—usually a scalar field—of a negative squared mass acquires a vacuum expectation value and reaches the minimum of the potential energy. ... In physics, the photon (from Greek φως phos, meaning light) is a quantum of the electromagnetic field, for instance light. ...

Orientation

Strings can also possess an orientation, which can be thought of as an internal "arrow" which distinguishes the string from one with the opposite orientation. By contrast, an unoriented string is one with no such arrow on it.

See also

• elementary particle
• brane
• list of string theory topics

In particle physics, an elementary particle is a particle of which other, larger particles are composed. ... Branes are objects in M-theory and its offshoot, brane cosmology. ... This is a list of string theory topics, by Wikipedia page. ...

References

• Schwarz, John (2000). "Introduction to Superstring Theory". Retrieved Dec. 12, 2005.

--Drewbarfield 07:29, 14 December 2005 (UTC)Drew Barfield