hi everyone(adsbygoogle = window.adsbygoogle || []).push({});

i'm brand new to forums and i'm holdin a seminar on a variation of the hilbert action as described in wald's book general relativity. if anyone knows that book and topic pretty well maybe you can help me, my question is this:

for the variation [itex]\delta R_{ab}[/itex] with respect to parameter [itex]\lambda[/itex] of the ricci tensor [itex]R_{ab} [/itex] wald uses a result from the end of chapter 7, where he assumes [itex] g_0^{ab}[/itex] to be a solution of einstein's equation, so in the calculation of [itex]\delta R_{ab}[/itex] he assumes already that [itex]R_{ab} = 0[/itex] at $\lambda = 0$ so he works it out in terms of the tensor [itex]C^c_{ab}[/itex] (the tensor difference between two covariant derivatives).

my problem is: he useseinstein's equationon the unperturbed metric to fish out [itex]\delta R_{ab}[/itex], then uses that to deriveeinstein's equationwith the hilbert action.

is there a good explanation for using this equation to derive this very same equation? i hope i explained myself clearly enough.

thanks in advance

**Physics Forums | Science Articles, Homework Help, Discussion**

Dismiss Notice

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Hilbert action according to robert wald

**Physics Forums | Science Articles, Homework Help, Discussion**