Light rays, gravitational waves, and pulse-time offsets

TL;DR

This paper investigates how gravitational waves can cause detectable pulse-time offsets in light signals, especially when emissions occur near the source, potentially enabling future observations of such effects.

Contribution

It develops a covariant framework in general relativity to analyze pulse-time offsets caused by gravitational waves, highlighting conditions for larger observable effects.

Findings

Offsets in pulse arrival times could reach 10^{-10} to 10^{-9} seconds.

Detectable effects are more significant when light emissions occur near the gravitational wave source.

Potential detection involves tight binary systems and nearby pulsars.

Abstract

One might expect light to be scattered when it passes through a gravitational wave, and might hope that in favourable circumstances these scatterings could be observed on Earth even if the interaction occurs far away. Damour and Esposito-Far\`ese, and Kopeikin, Sch\"afer, Gwinn and Eubanks, found that there were cancellations making such effects disappointingly small. Here I show that those cancellations depend on the emission of the light occurring far behind the gravity-wave source; for light-emissions near that source, larger effects are possible. I first develop a covariant treatment of the problem in exact general relativity (the propagation of light being modelled by geometric optics), and then specialise to linearised gravity. The most promising candidates identified here for detection in the not-too-distant future would involve sufficiently tight binaries as sources of gravitational radiation, and nearby pulsars as light-sources. In some favourable but not extreme cases, I find offsets in the pulses' times of arrival at Earth by ~ 10^{-10} -- 10^{-9} s, with periods half the binaries' periods.