How to reduce Einstein's equation for perfect fluids

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Discussion Overview

The discussion revolves around the reduction of Einstein's equation for perfect fluids using a specific metric. Participants explore the implications of this reduction in the context of general relativity, particularly regarding static uniform density stars.

Discussion Character

  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant presents a metric and claims it leads to a reduction of Einstein's equation to a specific system of equations involving the gravitational potential and fluid properties.
  • Another participant questions whether the original post is a homework question and prompts for evidence of independent effort.
  • A participant clarifies that the inquiry is based on an article, asserting that static uniform density stars must be spherical in general relativity.
  • Another participant requests clarification on the components of the metric, indicating uncertainty about the line element.

Areas of Agreement / Disagreement

The discussion shows a lack of consensus, with some participants seeking clarification while others assert claims based on external sources. Uncertainty remains regarding the specifics of the metric and its implications.

Contextual Notes

Participants express limitations in understanding the components of the metric and the implications of the equations presented. There is also a dependence on the definitions of terms like gravitational potential and perfect fluids.

Who May Find This Useful

This discussion may be useful for those interested in general relativity, particularly in the context of perfect fluids and the mathematical formulation of Einstein's equations.

joshyxc1979
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Using the metric $$ds^2=-V^2 dt^2 +g_{ab} dx^a dx^b$$, where $$g_{ij}$$ is the Riemannian metric of the constant t-surfaces, and V is the gravitational potential, show that Einstein's equation $$G_{ij}=8\pi T_{ij}$$ for perfect fluids reduces to the system
$$D^a D_a V= 4 \pi V( \rho +3p)\\
R_{ab}=V^{-1}D_a D_b V+4 \pi ( \rho -p) g_{ab}$$
Where $$D_a$$ and $$R_{ab}$$ are the three dimensional covariant derivative and Ricci curvature tensor associated with $$g_{ab}$$.
 
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Is this a homework question? Have you tried it yourself?
 
No its not a homework question, I read it in an article by J. of Math Phys 29 (2) feb 1988. Static uniform density stars must be spherical in GR
 
I'm sorry, could you write the whole line element? I don't know the components of g_{ij} expliclity.
 

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