= Bondi-Sachs formalism
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The Bondi-Sachs formalism uses outgoing <null hypersurfaces> to describe <gravitational radiation>. A <null coordinate> $u$ labels wavefronts, <areal radius> $r$ labels cross-sections, and angular coordinates label null generators.
The <Einstein field equations> split into radial relations and evolution equations for the angular geometry. At <future null infinity>, changing <Bondi shear> gives the <Bondi news function>, linking radiation to loss of <Bondi mass> in nonlinear <general relativity>.<Bondi-Sachs Formalism by Thomas Mädler and Jeffrey Winicour>[Sections 2–3: coordinates, hierarchy and asymptotic radiation]{ref}
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