Gravitational wave (GW) detection using gamma rays — A gamma ray clock

Gravitational waves are ripples in spacetime, caused by events like black hole mergers. They stretch and squeeze space as they pass through. While laser interferometers detect this by measuring tiny changes in distance, gamma-ray-based methods aim to detect the effects of GWs on energy levels or the propagation of gamma photons. Gamma-ray nuclear clocks are extremely sensitive to time dilationand changes in spacetime curvature. As a GW passes through a region of space, it can cause tiny shifts in the frequencyof nuclear transitions (i.e., gravitational redshift). These shifts cause phase or frequency modulations in the emitted gamma photons, which can be detected by comparing with a reference clock. If a gravitational wave changes the local passage of time even slightly, a gamma-ray clock might "tick" at a different rate, and the gamma photon frequency shifts reveal the wave’s presence [1].