# Duality

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## Duality (physics)

The state of having two natures, which is often applied in physics. The classic example is wave-particle duality. The elementary constituents of nature—electrons, quarks, photons, gravitons, and so on—behave in some respects like particles and in others like waves.

Duality is often used in a more precise sense. It indicates that two seemingly different, theoretical descriptions of a physical system are actually mathematically equivalent. Such an occurrence is very useful. Various properties and phenomena are clearer in one or the other of the descriptions, and calculations that are difficult or impossible in one description may be simple in the other. In the case of wave-particle duality, the wave description corresponds to a theory of quantized fields, where the field variables are governed by an uncertainty principle. The particle description corresponds to a Feynman integral over all particle paths in spacetime. The quantized-field and path integral theories sound very different but are mathematically equivalent, making identical predictions. See Feynman integral, Quantum field theory, Quantum mechanics, Uncertainty principle, Wave mechanics

#### Weak-strong duality

In some systems, there is weak-strong duality, meaning that when the coupling constant g of the original description is large that of the dual description, g, is small; for example g = 1/g. When g is large, so the interactions in the original description are strong and the perturbation theory in this description is highly inaccurate, then perturbation theory in the dual description gives a very accurate description.

#### Duality in superstring theory

It is believed that a complete theory of all particles and interactions must be based on quantization of one-dimensional objects (loops) rather than points: this is superstring theory. In superstring theory there is again the problem that perturbation theory is the main tool, giving an incomplete description of the physics. The situation has greatly improved with the discovery that weak-strong duality is a general property of string theory. In fact, there are five known string theories, and all are dual to one another. A notable feature in string theory is that in addition to strings and solitons, duality requires certain other objects as well: D-branes, which are local disturbances to which strings become fixed. Remarkably, the same methods have also been used to solve some long-standing problems regarding the quantum mechanics of black holes. See Quantum gravitation;, Superstring theory

References in periodicals archive ?
As a scenario for reducing labor market duality, the analysis considers the case in which the measure of duality used in the study goes back to its pre-bubble level of 5% (from 21% for the most recent available data).
The focus is on the ways through which the main elements of duality theory in advanced microeconomics are connected to each other.
Egudo: Proper efficiency and multi-objective duality in nonlinear programming, Journal of Information and Optimization Science, 8(1987), 155-166.
To relax convexity assumption imposed on the function in theorems on optimality and duality, various generalized convexity concepts have been proposed.
In contrast to the duality of spirit and substance, the duality of oppressors and oppressed develops in the operational area.
Because of the dynamic possibilities of DGS (Cabri 3D specifically), it is possible to consider the visualisation of regular solids duality with animation methods.
It is believed that for those firms experiencing poor performance in the pre-restructuring period will face significant pressures to not possess CEO duality status.
Very recently kurketal [13] have introduced V-[rho]--invexity concept generalizing V-invex function and studied weak and strong duality for non-smooth multiobjective programs.
Alawi added that the statement about Kirkuk given by Talabani is a result of "the duality in responsibilities, it is a constitutional duality, since the constitution which was written in a hurry is responsible for that result.
lt;p>Also, the questionnaire discovered that there is duality in granting licenses for the schools from ministries that have no relationship with the Education Ministry, and that there are student seat numbers for public exams given for unlicensed schools without permission from the ministry or Secretariat Capital.
Yazbek: The Duality Of Arms Gives Strength To Lebanon

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