e/Newtonian gauge

Information
has gloss	eng: In general relativity, Newtonian gauge is a perturbed form of the Friedmann-Robertson-Walker line element. The gauge freedom of general relativity is used to eliminate two scalar degrees of freedom of the metric, so that it can be written as :ds^2 =-(1+2\Psi)dt^2+a^2(t)(1-2\Phi)\delta_ab}dx^adx^b, where the Latin indices a and b are summed over the spatial directions and \delta_ab} is the Kronecker delta. Conformal Newtonian gauge is the closely related gauge in which :ds^2 =a^2(t)[-(1+2\Psi)d\tau^2+(1-2\Phi)\delta_ab}dx^adx^b] which is related by the simple transformation dt=a(t)d\tau. These metrics are perturbed forms of the Friedmann-Robertson-Walker metric. They are called Newtonian gauge because \Psi is the Newtonian gravitational potential of classical Newtonian gravity, which satisfies the Poisson equation \nabla^2\Psi=4\pi G\rho for non-relativistic matter and on scales where the expansion of the universe may be neglected.
lexicalization	eng: Newtonian gauge
instance of	c/Mathematical methods in general relativity