# Torsion in GR

1. Feb 8, 2008

### bchui

I ahve always wondered why only the curvature term $$R_{\mu,\nu}$$ been considered in GR. From differential Geoetry, how about the torsion tensor?

2. Feb 9, 2008

### joelperr

The simple answer is that in standard formulation of general relativity, we require a unique connection on a manifold which is torsion-free and metric compatible, which lead to the properties of the covariant derivative that we need.

3. Feb 13, 2008

### geoffc

It always bothered me as well that the torsion term was simply ignored. Many people have examined what happens when you keep the term, which has led to the Einstein-Cartan theory as a way to try and incorporate spin. Although this theory doesn't appear to be fundamental, it does seem to embed itself into supergravity which is in turn one of the limits of M-Theory.

Here is a link to Hehl's 1976 article from Rev. Mod Phs......
http://prola.aps.org/abstract/RMP/v48/i3/p393_1

And here is a much more recent article
http://arxiv.org/abs/0711.1535