Curvature and Stress-Energy: Solving the Einstein Equation with Tensor Densities

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Discussion Overview

The discussion revolves around the relationship between curvature and stress-energy in the context of the Einstein equation, exploring alternative formulations using tensor densities instead of traditional connections. The scope includes theoretical considerations of gravity, specifically within the frameworks of General Relativity and its variants, as well as gauge gravity theories.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant expresses dissatisfaction with the Christoffel-based covariant derivative, suggesting that the relationship between curvature and stress-energy could be expressed using oriented tensor densities without relying on connections.
  • Another participant introduces Einstein-Cartan gravity and mentions that it relaxes the requirement for a torsion-free connection, questioning whether this theory can be expressed without connections.
  • A participant notes that many gauge gravity theories are described as 10-dimensional brane theories, while they are more interested in 4-dimensional General Relativity and its variants.
  • One participant asserts that General Relativity fundamentally relies on connections due to the relationship between gravity, curvature, and parallel transport, and mentions the Weitzenbock connection in the context of torsion.

Areas of Agreement / Disagreement

Participants express differing views on the necessity of connections in General Relativity and related theories. There is no consensus on whether the Einstein equation can be reformulated without connections, and multiple competing perspectives on gravity theories are present.

Contextual Notes

Participants highlight limitations in their understanding of the implications of torsion in gravity theories and the specific requirements of different formulations. There is also uncertainty regarding the dimensionality and applicability of various gravity theories discussed.

Who May Find This Useful

This discussion may be of interest to those exploring advanced topics in theoretical physics, particularly in the areas of gravity, curvature, and the mathematical formulations of General Relativity and gauge theories.

Phrak
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The metric tensor is expressed in 10 independent elements. From this is obtained the Einstein equation once given 7 to 9 or so requirements imposed on the the connection and covariant derivative.

In my mind the Christoffel based covariant derivative is an ugly thing, good for a first attempt at understanding the connection between mass and gravity, but not the last word.

Instead: Can the relationship between curvature and stress-energy (The Einstein equuation,or something like it) be expressed in terms of oriented tensor densities with lower indices sans the goofey connections?
 
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Have you come across Einstein-Cartan gravity or any of the many versions of gauge gravity ? A web search will find plenty, and I attach one paper that I have to hand.
 

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As far as I know Einstein-Cartan gravity is Einstein gravity where the requirement that the connection be torsion-free (symmetric in it's lower indices) is relaxed. I was unable to tell, scanning the .pdf, whether this more general theory can be expressed without connections.

All gauge gravity sites I've visited seem to indicate that gauge/gravity are 10 dimensional brane theories. I was rather more interested in 4 dimensional General Relativity, or it's variants.

I may have misunderstood the directions in which you are pointing.
 
All gauge gravity sites I've visited seem to indicate that gauge/gravity are 10 dimensional brane theories. I was rather more interested in 4 dimensional General Relativity, or it's variants.

Not what I meant at all. Here's a couple more references. I don't think GR is possible without connections because in GR gravity->curvature->parallel transport->connection ( but not necessarily in that order).
If the gravitational field is in the torsion, the Weitzenbock connection is used ( but there's no geodesics).

arXiv:gr-qc/0011087v1
arXiv:gr-qc/9602013 v1

Look for more work by the authors of these papers.
 

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