Register to reply 
Second order expansion of metric in freefallby InsertName
Tags: metric 
Share this thread: 
#1
Dec2212, 06:59 AM

P: 27

Hello,
I have read that, in a freelyfalling frame, the metric/ interval will be of the form: ds^{2} = c^{2}dt^{2}(1 + R_{0i0j}x^{i}x^{j})  2cdtdx^{i}([itex]\frac{2}{3}[/itex] R_{0jik}x^{j}x^{k}) + (dx^{i}dx^{j}(δ_{ij}  [itex]\frac{1}{3}[/itex] R_{ikjl}x^{k}x^{l}) to second order. Does anyone know where I could find a derivation of this result? 


#2
Dec2212, 02:40 PM

Sci Advisor
Thanks
P: 4,160

InsertName, That's an interesting formula! It's derivation is almost immediate, except I have doubts about the absence of the time coordinate, and the factors of 1/3.
Expand the metric in a Taylor's series: g_{μν} = A_{μν} + B_{μνσ}x^{σ} + C_{μσντ}x^{σ}x^{τ} + ... It's always possible to choose coordinates such that A_{μν} = η_{μν} and B_{μνσ} = 0, and in these coordinates the Christoffel symbols vanish. Then the formula for the Riemann tensor reduces to R_{μσντ} = ½(g_{μτ,σν} + g_{σν,μτ}  g_{μν,στ}  g_{στ,μν}) = C_{μστν} + C_{τνμσ}  C_{μσντ}  C_{σμτν}. If you assume C to have the same symmetry as the Riemann tensor, then this is 4C_{μστν}, showing that C_{μστν} = (1/4)R_{μσντ} 


Register to reply 
Related Discussions  
MultiVariable Second Order Taylor Series Expansion, Ignoring SOME second order terms  Differential Equations  6  
Free Fall Question (Nonsolvable 2nd order equation)  Introductory Physics Homework  3  
Metric for an observer in free fall two schwarzchild radii from black hole.  General Physics  1  
Swartzchild metric and free fall  Special & General Relativity  9  
Metric expansion  Special & General Relativity  18 