- #1

WannabeNewton

Science Advisor

- 5,815

- 543

__A First Course in General Relativity__, the use of the weak field approximation is confusing to me. I constantly get confused when the term "f(x) is only valid to first order in f..." for the Newtonian potential in the metric comes up. At a certain point the book states:

...1/2(-1/(1 + 2[tex]\phi[/tex]))(-2[tex]\phi[/tex]),0 (where ,0 is the time derivative)

and then the book simplifies this to:

[tex]\phi[/tex],0 + 0([tex]\phi[/tex][tex]^{2}[/tex])

I have NO IDEA how that step came about. Does this step and the whole "correct to first order" have to do with a Taylor expansion and if so how does one come to what the book came to? Thanks.