  We extend the geometrical ideas of the spacetime deformations to study the
physical foundation of the post-Riemannian geometry. To this aim, we construct
the theory of 'two-step spacetime deformation' as a guiding principle. We
address the theory of teleparallel gravity and construct a consistent
Einstein-Cartan (EC) theory with the 'dynamical torsion'. We show that the
equations of the standard EC theory, in which the equation defining torsion is
the algebraic type and, in fact, no propagation of torsion is allowed, can be
equivalently replaced by the set of 'modified EC equations' in which the
torsion, in general, is dynamical. The special physical constraint imposed upon
the spacetime deformations yields the short-range propagating spin-spin
interaction.

General Relativity and Quantum Cosmology