The existing gravitational wave detectors, LIGO and Virgo, using long arms along which laser light travels to measure exquisitly small variations in length, are very expensive and complex devices. A new idea has been proposed to design a detector using the scattering effect on light photons of (still hypothetical) gravitons. This could potentially be a much cheaper, simpler device. If it worked it would also reveal a lot about gravitons and help to marry quantum physics and relativistic spacetime – an elusive but much pursued aim. It would also cast some light on th issue of whether gravitons are massless – moving at the speed of light, or have a small mass themselves and move slightly slower – the massive gravity theories. It would also have bearing on dark matter and dark energy.