Daedalus: Gravity waving to us

Physicists are still exasperated by the elusiveness of gravitational waves. Laser interferometers and resonating metal bars have so far failed to detect them. Einstein showed that a gravitational field can be detected by its bending of light. A distant galaxy in the same line of sight as a nearer one can form an 'Einstein ring' image around it; the light is deviated in passing through the nearer galaxy's gravitational field. If an Einstein ring is ever found around an empty patch of sky, a clump of dark matter will have been discovered. Similarly, says Daedalus, the light from a distant star or galaxy should be deviated in phase with any gravitational waves through which that light passes. An observer would see the object apparently vibrating back-and-forth in the sky, in time with the gravitational waves.