Cartan's Torsion: Necessity and Observational Evidence

This article starts with the mathematical definition, concrete description, and physical meaning of Cartan's torsion. I proceed with the argumentation that torsion is required for the description of intrinsic spin. Moreover I argue that the duality between curvature and torsion is analogous to the duality between electricity and magnetism. I conclude this article by pointing out that the aligned rotation axes of the galaxies of the Perseus-Pisces supercluster may be interpreted as a topological defect generated by torsion.