The Persistence of Nonlinear Gravitational Wave Memory

TL;DR

This paper explores the nonlinear gravitational wave memory effect, revealing that it causes a permanent displacement in test masses but diminishes over time due to echoes, highlighting complex nonlinear dynamics.

Contribution

It demonstrates that nonlinear gravitational wave memory vanishes at late times in a sea of echoes, challenging previous assumptions about its permanence.

Findings

Memory causes permanent displacement of test masses

Memory diminishes over time due to echoes

Nonlinear features are crucial in gravitational wave behavior

Abstract

Nonlinear gravitational wave memory is a surprise of theoretical physics. Whereas it is understood that a gravitational wave induces oscillatory squeezing and stretching motion in a collection of freely-falling test masses, it is unexpected that the wave leaves a residual displacement of the test masses. This displacement is the tribute in memoriam to the passing wave. The memory originates in a nonlinear feature of gravitation. Whilst merging black holes are a significant source of gravitational waves, the gravitational wave energy itself is a further source of gravitational waves. The memory is often described as a permanent displacement of the test masses caused by a burst of primary gravitational waves. But as we show, memory vanishes at late times in a sea of echoes.