Weak and Strong Coupling
In a quantum field theory with a dimensionless coupling constant g, if g ≪ 1 (g is much smaller than one) then the theory is said to be weakly coupled. In this case it is well described by an expansion in powers of g, called perturbation theory. If the coupling constant is of order one or larger, the theory is said to be strongly coupled. An example of the latter is the hadronic theory of strong interactions (which is why it is called strong in the first place). In such a case non-perturbative methods have to be used to investigate the theory.
Read more about this topic: Coupling Constant
Famous quotes containing the words weak and, weak, strong and/or coupling:
“When cowardice is made respectable, its followers are without number both from among the weak and the strong; it easily becomes a fashion.”
—Eric Hoffer (1902–1983)
“Royalty is a government in which the attention of the nation is concentrated on one person doing interesting actions. A Republic is a government in which that attention is divided between many, who are all doing uninteresting actions. Accordingly, so long as the human heart is strong and the human reason weak, Royalty will be strong because it appeals to diffused feeling, and Republics weak because they appeal to the understanding.”
—Walter Bagehot (1826–1877)
“When the ivy has found its tower, when the delicate creeper has found its strong wall, we know how the parasite plants grow and prosper.”
—Anthony Trollope (1815–1882)
“The time of the seasons and the constellations
The time of milking and the time of harvest
The time of the coupling of man and woman
And that of beasts. Feet rising and falling.
Eating and drinking. Dung and death.”
—T.S. (Thomas Stearns)