Bondi-Sachs Formalism

TL;DR

The Bondi-Sachs formalism in General Relativity offers a null-coordinate approach that demonstrated gravitational radiation as a nonlinear effect and revealed the extended symmetry group at null infinity.

Contribution

It introduced a metric-based formalism adapted to null geodesics, showing gravitational waves cause mass loss and uncovering the BMS symmetry group.

Findings

Gravitational radiation is a nonlinear effect.

Emission of gravitational waves leads to mass loss.

The symmetry group at null infinity is larger than Poincare.

Abstract

The Bondi-Sachs formalism of General Relativity is a metric-based treatment of the Einstein equations in which the coordinates are adapted to the null geodesics of the spacetime. It provided the first convincing evidence that gravitational radiation is a nonlinear effect of general relativity and that the emission of gravitational waves from an isolated system is accompanied by a mass loss from the system. The asymptotic behaviour of the Bondi-Sachs metric revealed the existence of the symmetry group at null infinity, the Bondi-Metzner-Sachs group, which turned out to be larger than the Poincare group.