  We describe how the presence of the antisymmetric tensor (torsion) on the
world sheet action of string theory renders the size of the target space a
gauge non invariant quantity. This generalizes the R <--> 1/R symmetry in which
momenta and windings are exchanged, to the whole O(d,d,Z). The crucial point is
that, with a transformation, it is possible always to have all of the lowest
eigenvalues of the Hamiltonian to be momentum modes. We interpret this in the
framework of noncommutative geometry, in which algebras take the place of point
spaces, and of the spectral action principle for which the eigenvalues of the
Dirac operator are the fundamental objects, out of which the theory is
constructed. A quantum observer, in the presence of many low energy eigenvalues
of the Dirac operator (and hence of the Hamiltonian) will always interpreted
the target space of the string theory as effectively uncompactified.
