superstring theory


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Superstring theory

A proposal for a unified theory of all interactions, including gravity. At present, the strong, weak, and electromagnetic interactions are accounted for within the framework of the standard model. This model correctly describes experiments up to the highest energies performed so far, and gives a complete description of the elementary particles and their interactions down to distances of the order of 10-18 m. Nevertheless, it has serious limitations, and attempts to overcome them and to unify the forces of nature have been only partly successful. Moreover, these attempts have left standing fundamental difficulties in reconciling gravitation and the laws of quantum mechanics. Superstring theory represents an ambitious program to unify all of the interactions observed in nature, including gravitation, in a theory with no unexplained parameters. In other words, this theory, if successful, should be able to account for all of the particles observed in nature and their interactions. See Elementary particle, Fundamental interactions

String concept

In string theory, the fundamental objects are not point particles, as in standard theories of elementary particles, but one-dimensional extended objects, the open and closed strings. In such a theory, what are usually called the elementary particles are simply particular quantum states of the string. In superstring theories, space-time is ten-dimensional (space is nine-dimensional). If such theories are to describe nature, six dimensions must be “curled up” or “compact.” The main consequence of such extra dimensions is the existence of certain very massive particles. See Space-time

The essential features of string theories can be understood by analogy with the strings of a musical instrument. Such strings vibrate at a characteristic frequency, as well as any integer multiple of that frequency. Each of these modes of vibration (so-called normal modes) can be excited by plucking or striking the string. In classical physics, the amplitudes of vibration of each mode can take on a continuum of values. If there were a string of atomic dimensions, subject to the laws of quantum mechanics, the energies of this quantum string could take on only discrete values, corresponding to particular quantum states. See Quantum mechanics, Vibration

The strings of superstring theory are quite similar. The main difference is that they obey Einstein's principles of special relativity. As a result, since each quantum state has a particular energy, it has a definite mass. Thus, each state of the string behaves as a particle of definite mass. Because it is possible, in principle, to pump an arbitrarily large amount of energy into the string, the theory contains an infinity of different types of particles of arbitrarily large mass. The interactions of these particles are governed by the ways in which the strings themselves interact. To be consistent with the principles of relativity, a string can interact only by splitting into two strings or by joining together with another string to form a third string. As a result, the interactions of strings are nearly unique. This geometric picture of string interactions translates into a precise set of rules for calculating the interaction of individual string states, that is, particles. See Relativity

Classical solutions

Obtaining a description of superstring theory analogous to quantum field theory is an active topic of research. However, even though the equations that describe this field theory are not completely known at present, it is known how to find classical solutions of these equations, and by various techniques, an enormous number of such solutions have been found. These include states in which space-time has any dimension between one and ten, and states with many bizarre symmetries and spectra. Each of these solutions then corresponds to a possible ground state of the system. The theories built around some of these states look very much like the real world. Not only are four dimensions flat while six are compact, but they possess gauge symmetries close to that of the standard model. Some have three or four generations of quarks and leptons, as well as light Higgs particles, which are of crucial importance in the standard model. Many of these solutions possess space-time supersymmetry. See Higgs boson, Lepton, Quarks

However, if the theory does describe nature, it must have some mechanism that chooses one of the possible ground states. Because the masses and couplings of the elementary particles depend only on the choice of ground state, determining this true ground state will yield a set of predictions for these quantities. If string theory is a correct theory, these predictions must agree with the experimental values.

superstring theory

(soo -per-string) See string theory.

superstring theory

[′sü·pər‚striŋ ‚thē·ə·rē]
(particle physics)
A theory of elementary particles which obeys supersymmetry and in which the particles are one-dimensional, closed curves with zero thickness and length of the order of the Planck length, 10-35 m.
References in periodicals archive ?
Based on the observation that the two different theoretical results agree, it has been concluded that the results obtained by the calculation in Maldacena's theory include the quantum gravity effects correctly as the calculation in conventional superstring theory does.
There is a possible analogy here to the way the "Minimally Supersymmetric Standard Model" (MSSM) really is a whole class of theories, in this case defined (as stated by superstring theory critic Lee Smolin in a quotation in the Part II chapter on "The Problem of Parameters," p.
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For the first time Superstring theory was formulated in 1968 by Gabriele Veneziano, young Italian physicist who worked in CERN and studied strong nuclear interactions [14].
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(5.) Green MB, Schwarz JH and Witten E: "Superstring Theory: Volume 1." Cambridge, p14, 1988.
"Superstring theory has revolutionized speculation about the physical world by suggesting that strings play a pivotal role in the universe.
[10, 11] were able to prove that there are theoretical links, such that the Superstring theory reduces to AdS/CFT theory, and Ads/CFT theory reduces to the so-called Light Front Holography, which in turn this model can serve as first approximation to the Quantum Chromodynamics theory.
Designed for graduate students and researchers in the fields of cognitive science, economics, finance, psychology and political science, this volume also describes probability models that can be applied to superstring theory and quantum cosmology.
Witten, Superstring theory, Cambridge University Press, 1978.Page 25.
The concept is called "superstring theory," because theoreticians imagine the core components of the universe as tiny loops of string or membranes vibrating in 11 dimensions.
In this best-selling book (voted one of the best science books of the year by the New York Times and the Washington Post), Kaku explores the mathematics of higher dimensions (hyperspace), illuminating superstring theory in the process.