  We follow the point of view that superstring theory, as the theory of quantum
gravity in the number of spacetime dimensions bigger than 4, serves as
mathematics for both, 4 dimensional QG and exotic smoothness on open
4-manifolds. Extra-dimensions, supersymmetry or some other string techniques,
belong to the mathematical toolkit suitable for the above purposes. Physics in
dimension 4 is reached via exotic 4-geometries on $\mathbb{R}^4$. In the paper
we discuss the techniques of exact superstring backgrounds, CFT and $SU(2)_k$
WZW models, as suitable for the description of effects assigned to the magnetic
field and its gravitational backreactions on exotic Euklidean $\mathbb{R}^4$
which is the underlying smoothness for the 4-dimensional spacetime.
