Flat Space - Christoffel symbols and Ricci = 0?

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Homework Help Overview

The discussion revolves around the calculation of Christoffel symbols and the Ricci tensor in the context of general relativity, specifically focusing on a metric that may represent flat space. The original poster seeks to find a transformation to the standard flat space metric form.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • The original poster attempts to calculate the Christoffel symbols and Ricci tensor, noting that the metric components are constants, which leads to the conclusion that both are zero. They express uncertainty regarding the transformation to flat space. Other participants suggest exploring linear transformations and propose specific forms for new coordinates to facilitate this transformation.

Discussion Status

Participants are actively engaging with the problem, providing insights and suggestions for the transformation approach. There is a collaborative atmosphere with multiple participants confirming each other's ideas, although no explicit consensus has been reached on the method to achieve the transformation.

Contextual Notes

The original poster is new to general relativity and is navigating the complexities of the topic, indicating a learning process that involves grappling with foundational concepts and mathematical formulations.

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Homework Statement


[/B]
(a) Find christoffel symbols and ricci tensor
(b) Find the transformation to the usual flat space form ## g_{\mu v} = diag (-1,1,1,1)##.

ricci1.png

Homework Equations

The Attempt at a Solution



Part(a)
[/B]
I have found the metric to be ## g_{tt} = g^{tt} = -1, g_{xt} = g_{tx} = 2c, g_{xx} = g^{xx} = 0, g_{yy} = g^{yy} = 1, g_{zz} = g^{zz} = 1##.

The christoffel symbols can be calculated by:
\Gamma_{\alpha \beta}^{\mu} = \frac{1}{2} g^{\mu v} \left( \frac{\partial g_{\alpha v}}{\partial x^{\beta}} + \frac{\partial g_{v \beta}}{\partial x^{\alpha}} - \frac{\partial g_{\alpha \beta}}{\partial x^{v}} \right)

Since all components of the metric are constants, it means ##\Gamma_{\alpha \beta}^{\mu} = 0## and ##R_{\alpha \beta}^{\mu} = 0##.

Part (b)

I'm not sure how to approach this question. I know I have to find the Jacobian ##\frac{\partial \tilde{x^{\mu}}}{\partial x^{v}}##. I also know the transformation is ##\tilde{g_{\alpha \beta}} = \frac{\partial x^{\mu}}{\partial \tilde{x^{\alpha}}} \frac{\partial x^v}{\partial \tilde{x^{\beta}}} g_{\mu v}##.
 
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Any input for part (b)?
 
For both the original line element and the usual flat space line element the metric components are constants. This suggests a linear transformation. So, maybe introduce a new time coordinate ##\tilde{t} = at + bx## where you can try to find values of ##a## and ##b## to do the job.
 
TSny said:
For both the original line element and the usual flat space line element the metric components are constants. This suggests a linear transformation. So, maybe introduce a new time coordinate ##\tilde{t} = at + bx## where you can try to find values of ##a## and ##b## to do the job.

Letting ## c \tilde t = c t - x## makes it work because ##c^2 d \tilde t^2 = c^2dt^2 - 2ct ~dt dx + dx^2##.
 
Last edited:
Looks right.
 
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TSny said:
Looks right.

Thanks a lot for all your help! I'm just starting out in GR so I'm learning as hard as I can.
 

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