A classical string is a one-dimensional extended object existing in four-dimensional space-time. A typical example of a classical string is a piece of thread.
A classical string is specified by the string tension T, and can exist in a space-time of arbitrary dimension. Quantum strings can only exist in certain critical space-time dimensions such as 26 and 10. Quantum bosonic strings can be made supersymmetric yielding the superstring.
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All of physical reality is made out of different states of the superstring. Roughly speaking, each vibrational mode of the string can be thought of as a point particle. Hence, one superstring gives rise to infinitely many local fermion and boson fields. All of the observed bosons and fermions can be cosidered as a vibrational mode of the fundamental superstring. It must be noted that the string is both constituent and interaction. Superstrings can be either open or closed. |
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Quantum strings inherently contain a quantum theory of gravity! For this purpose, the size of the strings must be of Planck length scale.
Consider a particle at the point x0. Conventionally, the properties of the point-particle are then specified by a field A(x0).
However, for a string, we have to determine infinitely many points (along the whole string). This is fundamentally the reason why a single string in effect yields infinitely may point-like particles.
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According to the big bang theory, we have the following scenario : Universe starts from a point -> Strings -> Inflation -> Gravity differentiates -> Further differentiation. Since strings occur before any differentiation, they must of Planck scale (10-35m), the distance at which all the forces are equally strong. |
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| Note : Distances are inversely related to energy by the uncertainty principle (the smaller the distance, the higher the energy scale). | |
Quantized Strings
D-Branes
Superstring
Particle Spectrum
String Interaction : Topology vs
GeometryLast updated: 03 March, 2000
