Hi,(adsbygoogle = window.adsbygoogle || []).push({});

I have a question concerning the Wald's book: General Relativity.

In the appendix E, he derived the Einstein equation by considering the surface term (GHY).

I do not understand what he said after the equation (E.1.38).

Actually he considers that [itex]h^{bc}\nabla_c(\delta g_{ab})=0[/itex], because we fix [itex]\delta g_{ab}=0[/itex] on the surface, but therefore why the other term in (E.1.38) is not null, the term [itex]h^{bc}\nabla_a(\delta g_{bc})[/itex].

They look the same for me, and after some algebra, where we replace the covariant derivative by the one compatible with the metric on the surface we should have a total derivative term on the surface that we can integrate away.

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!

# Clarification on Wald's book

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