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## Trace of SEM tensor

Hi,

Let $T_{\alpha\beta}$ be the stress-energy momentum tensor. What does $g_{\alpha\beta}T^{\alpha\beta}$ mean? I have always thought of the Ricci tensor and the SEM as the same thing essentially, but the Ricci scalar essentially assigns a number to the curvature of the manifold, what does $T$ say?

Thanks,

 PhysOrg.com science news on PhysOrg.com >> Front-row seats to climate change>> Attacking MRSA with metals from antibacterial clays>> New formula invented for microscope viewing, substitutes for federally controlled drug
 Recognitions: Science Advisor I don't know in GR, but Nordstrom's scalar gravitation, the first consistent relativistic theory of gravity, can be reformulated using the Ricci Scalar and the trace SEM. It doesn't match observation, but it's historically interesting. See Eq 16 of http://arxiv.org/abs/gr-qc/0405030
 Recognitions: Science Advisor Another random fact is that CFTs and Maxwell's equations have traceless SEMs.

Recognitions:
Gold Member

## Trace of SEM tensor

Thanks atyy for those references and tit-bits. I'm going to bump to see if I can get anything else.