= Retarded quadrupole field
{title2=$\bar h_{ij}(t,\mathbf x)\simeq 2\ddot I_{ij}(t-r)/r$}
For a compact slowly moving source in the <weak-field approximation>, with no incoming homogeneous wave and $G=c=1$, the retarded <Linearized Einstein equations> give this leading far-zone <trace-reversed metric perturbation>. The key consequence of <stress-energy conservation> is $\ddot I_{ij}=2\int T_{ij}\,d^3x$. The physical <gravitational wave> is obtained by the <transverse-traceless projector>.
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