B Find Geodesics in Dynamic Ellis Orbits Metric

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The discussion revolves around finding geodesics in the dynamic Ellis orbits metric, specifically the metric ds² = -dt² + dp² + (5p² + 4t²)dφ², with a focus on those with nonzero angular momentum. Participants explore the feasibility of using previously discussed techniques from the FLRW metric, particularly the geodesic Lagrangian method, which simplifies calculations by eliminating certain derivatives. There is a consensus that while the Lagrangian method can be beneficial, the absence of Killing fields for t and p complicates the integration of geodesics. The conversation highlights the importance of understanding the underlying equations rather than seeking shortcuts, emphasizing that some differential equations can be solved exactly while others cannot. Overall, the thread underscores the complexity of the problem and the necessity of rigorous mathematical approaches in general relativity.
  • #91
I'm sure you have written it down. But where did it enter your differential equations? What would be different about them if the LHS was not zero? Or to put it another way, if you had used ##\mathcal{L}'=\mathcal{L}\pm 1## instead?

I don't see why the substitution wouldn't work, as long as you understand that you've introduced a third angular coordinate that isn't an angle in spacetime in any meaningful sense. I just suspect that inserting you null/timelike/spacelike constraint will be messy.

I'd be very doubtful of anything passing through the origin, but that's an issue with the spacetime not the maths.
 
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  • #92
Ibix said:
I'm sure you have written it down. But where did it enter your differential equations? What would be different about them if the LHS was not zero? Or to put it another way, if you had used ##\mathcal{L}'=\mathcal{L}\pm 1## instead?

I don't see why the substitution wouldn't work, as long as you understand that you've introduced a third angular coordinate that isn't an angle in spacetime in any meaningful sense. I just suspect that inserting you null/timelike/spacelike constraint will be messy.

I'd be very doubtful of anything passing through the origin, but that's an issue with the spacetime not the maths.

Ibix said:
I'm sure you have written it down. But where did it enter your differential equations? What would be different about them if the LHS was not zero? Or to put it another way, if you had used ##\mathcal{L}'=\mathcal{L}\pm 1## instead?

I don't see why the substitution wouldn't work, as long as you understand that you've introduced a third angular coordinate that isn't an angle in spacetime in any meaningful sense. I just suspect that inserting you null/timelike/spacelike constraint will be messy.

I'd be very doubtful of anything passing through the origin, but that's an issue with the spacetime not the maths.
Actually, I was wrong about substituting the trig functions yielding the desired result. Honestly I feel like ##t^2+p^2=f(\lambda)## might be as far as I can get in terms of anything exact. But that is probably enough. By the way, what do you mean by LHS?
 
  • #93
Onyx said:
By the way, what do you mean by LHS?
Left Hand Side. It's a completely standard abbreviation.
 

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