Torsion Gravity: a Reappraisal

TL;DR

This paper critically reviews the role of torsion in gravity, compares different theories including teleparallel gravity and Einstein-Cartan, and discusses their implications for understanding gravitational degrees of freedom.

Contribution

It provides a comprehensive reappraisal of torsion in gravity, advocating for the teleparallel perspective as a complete description of gravitational phenomena.

Findings

Teleparallel gravity describes gravity via torsion instead of curvature.

The teleparallel approach aligns with the strong equivalence principle.

General relativity remains a complete theory of gravity.

Abstract

The role played by torsion in gravitation is critically reviewed. After a description of the problems and controversies involving the physics of torsion, a comprehensive presentation of the teleparallel equivalent of general relativity is made. According to this theory, curvature and torsion are alternative ways of describing the gravitational field, and consequently related to the same degrees of freedom of gravity. However, more general gravity theories, like for example Einstein-Cartan and gauge theories for the Poincare and the affine groups, consider curvature and torsion as representing independent degrees of freedom. By using an active version of the strong equivalence principle, a possible solution to this conceptual question is reviewed. This solution favors ultimately the teleparallel point of view, and consequently the completeness of general relativity. A discussion of the consequences for gravitation is presented.