What is Coupling constant?
{{quantum field theory}} Every [[force]] has a '''coupling constant''', which is a [[Measurement|measure]] of its [[Intensity (physics)|strength]] in an [[Fundamental force|interaction]]. The coupling constant determines the [[Probability|chance]]s of one [[particle]] to [[Emission|emit]] or [[Absorption|absorb]] another particle. In [[electromagnetism]], for example, the coupling constant is based on the [[electric charge]]. A coupling constant plays an important role in [[Dynamics (mechanics)|dynamics]]. When physicists study the [[Quantum electrodynamics|quantum behaviour of electromagnetism]], they can not solve the whole theory exactly, because every particle may emit and absorb many other particles, which may also do the same, endlessly. So events of emission and absorption are considered as [[Perturbation theory|perturbations]] and are dealt with by a series of [[approximation]]s. This also can happen in [[string theory]]. String theories have a coupling constant. It determines the probability that a 1-dimensional string of [[energy]] will separate into ''two'' separate energy strings. But unlike in particle theories, the string coupling constant is not just a number, but depends on one of the [[oscillation]] modes of the string. [[Category:Quantum mechanics]] [[Category:Statistics]] {{physics-stub}}