
T Duality
T
duality was the major discovery during the period between string
revolutions from 19861992. The simplest case has one compact dimension
— a circle of radius R.
Momentum excitations: E_{n}
= n/R
Winding mode excitations: E_{m}
= 2 p T R m
T is the string tension T = (2 p
L_{st}^{2})^{1}
T duality is the invariance of a theory
under switching m with n
and R with L_{st}^{2}/R.
The implication of T duality is that
quantum geometry at short distances falls under a new Generalized Uncertainty
Principle:

