Solution strategy for linearized gravity problem

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SUMMARY

The discussion focuses on solving a problem related to linearized gravity, specifically the metric for a moving mass and the trajectory of a photon in its gravitational field. The metric is given as $$ds^2 = -(1 + 2 \phi)dt^2 + (1-2\phi)\delta_{ij}dx^i dx^j$$ with $$\phi = -GM/(x^2 + y^2 + z^2) \ll 1$$. Participants emphasize the importance of transforming to the rest frame of the moving mass and the limitations of the Lorentz transformation in non-Minkowski spacetimes. The conversation highlights the necessity of understanding the Riemann tensor and the Lorentz gauge conditions for accurate transformations in linearized gravity.

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  • Understanding of linearized gravity concepts
  • Familiarity with Lorentz transformations and their limitations
  • Knowledge of Riemann tensor and its implications in curved spacetime
  • Ability to work with geodesic equations in general relativity
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  • Study the derivation of the Riemann tensor in linearized gravity
  • Learn about the Lorentz gauge conditions as discussed in MTW
  • Explore the geodesic equation and its applications in gravitational fields
  • Review Chapter 6 of Carroll's lecture notes on linearized gravity for additional insights
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  • #31
Jonsson said:
That is a good thing, because we are not interested in all null paths.

Isn't a photon trajectory a null path?

Jonsson said:
Yes, I agree these solve (*), but why is it important that you've found exactly one solution that don't interest us?

Because what I found isn't a geodesic but is a solution to (*). So (*) isn't a complete specification of the geodesic problem statement.

Jonsson said:
Can you propose some strategy that will work?

yes, solve the geodesic problem for the metric you've been given then transform the answer to the ##M## is in motion frame?
 
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  • #32
Paul Colby said:
yes, solve the geodesic problem for the metric you've been given then transform the answer to the ##M## is in motion frame?

Thanks. I found the deflection angle is ##\frac{4GM}{b}##. How do you say I transform this quantity back?
 

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