Via the relative shift between the wave crests of the two partial waves, Michelson's interferometer reacts very sensitively to changes in the length of one of its arms.

In the model interferometer in this exhibition, you have the possibility of lengthening or shortening one of the interferometer arms by no more than 1.5 of a millionth of a metre - and you can observe how even this small shift influences the interference pattern!

In interferometric gravitational wave detectors, the same principle is used to detect systematic changes in distance caused by gravitational waves, shifting the partial waves relative to each other. There, the goal is to detect, with the help of advanced interferometry, changes in length amounting to no more than one billionth of a trillionth of a metre - a fraction of the diameter of an atomic nucleus!