Figure 1: Schematic configuration of three freely-falling particles as a detector of gravitational waves.
The particles are labelled 1, 2, and 3, their positions with respect to the origin O of the coordinate
system are given by 3-vectors . The Euclidean separations between the particles
are denoted by , where the index corresponds to the opposite particle. The unit 3-vectors
point between pairs of particles, with the orientation indicated.