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

  • Thread starter Phrak
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In summary, the conversation discusses the metric tensor and the Einstein equation, which can be obtained by imposing requirements on the connection and covariant derivative. The Christoffel based covariant derivative is considered to be an imperfect solution for understanding the relationship between mass and gravity. The possibility of expressing this relationship in terms of oriented tensor densities without connections is raised, and the concept of Einstein-Cartan gravity is mentioned. The idea of gauge gravity as a 10-dimensional brane theory is also discussed, but the focus is on 4-dimensional General Relativity. The conversation ends with the suggestion to look for more work by certain authors in this field.
  • #1
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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  • #2
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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  • #3
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.
 
  • #4
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.
 

1. What is the Einstein equation and what does it represent?

The Einstein equation is a fundamental equation in the field of general relativity, which describes the relationship between the curvature of spacetime and the distribution of matter and energy. It is represented by the equation, Gμν = 8πTμν, where Gμν is the Einstein tensor and Tμν is the stress-energy tensor.

2. What are tensor densities and how are they used in solving the Einstein equation?

Tensor densities are mathematical objects that are used in the formulation of the Einstein equation to account for the changes in volume and orientation of the coordinate system. They are essential in general relativity as they allow us to describe physical quantities that are independent of the choice of coordinates.

3. How does the Einstein equation relate to the concept of spacetime curvature?

The Einstein equation is a mathematical expression of how the distribution of matter and energy in a given region of spacetime affects the curvature of that region. It tells us that matter and energy are the source of spacetime curvature, and the more concentrated they are, the stronger the curvature will be.

4. Can the Einstein equation be solved for any distribution of matter and energy?

Yes, the Einstein equation can be solved for any distribution of matter and energy. However, it becomes increasingly complex for more complicated distributions, such as those that involve multiple masses or moving objects. In these cases, numerical methods are often used to approximate solutions.

5. What are the implications of solving the Einstein equation for our understanding of the universe?

Solving the Einstein equation has allowed us to make significant advancements in our understanding of the universe, particularly in the field of general relativity. It has helped us explain various phenomena, such as gravity, the bending of light, and the expansion of the universe. It also plays a crucial role in modern theories of cosmology and the search for a unified theory of physics.

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