Sketch of the interferometric set-up for light under the influence of a gravitational wave. Credit: B. Schröder/HZDR When massive objects such as black holes merge or neutron stars collide, they can send gravitational waves rippling through the universe. These waves travel at the speed of light and cause extremely small distortions in space-time. Albert Einstein predicted their existence more than a century ago, but scientists did not directly observe them until 2015. Now, Prof. Ralf Schützhold,