Gravitational memory is a persistent change in the relative configuration of freely falling bodies after a gravitational-wave burst has passed. In the weak-field transverse-traceless description, an initially separated pair obeys . A nonzero net strain change leaves a displacement rather than only a temporary oscillation.
Memory can arise from changes in the motion of material sources and from the energy carried away by radiation itself. The latter contribution reflects the nonlinear gravitational role of wave energy. Distinguishing this slow or step-like response from detector drift requires more than identifying an oscillatory waveform.[ref]
Gravitational Memory, BMS Supertranslations and Soft Theorems by Andrew Strominger and Alexander Zhiboedov. Introduction and Section 4.2, inertial detector displacement memory
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