Editing Compactification (physics) (section)

==In string theory==

In string theory, compactification is a generalization of [[Kaluza–Klein theory]].<ref>[[Dean Rickles]] (2014). ''A Brief History of String Theory: From Dual Models to M-Theory.'' Springer, p. 89 n. 44.</ref> It tries to reconcile the gap between the conception of our universe based on its four observable dimensions with the ten, eleven, or twenty-six dimensions which theoretical equations lead us to suppose the universe is made with.

For this purpose it is assumed the [[String theory#Extra dimensions|extra dimensions]] are "wrapped" up on themselves, or "curled" up on [[Calabi–Yau manifold|Calabi–Yau spaces]], or on [[orbifold]]s. Models in which the compact directions support [[flux]]es are known as ''flux compactifications''. The [[coupling constant]] of [[string theory]], which determines the probability of strings splitting and reconnecting, can be described by a [[Field (physics)|field]] called a [[dilaton]]. This in turn can be described as the size of an extra (eleventh) dimension which is compact. In this way, the ten-dimensional [[String theory#Dualities|type IIA string theory]] can be described as the compactification of [[M-theory]] in eleven dimensions. Furthermore, [[String theory#Dualities|different versions of string theory]] are related by different compactifications in a procedure known as [[T-duality]].

The formulation of more precise versions of the meaning of compactification in this context has been promoted by discoveries such as the mysterious duality.