  Milne’s philosophy of cosmology came with a closely associated cosmological model, kinematic relativity, so-called because of its tight links to the kinematics of Einstein’s Special Theory of Relativity. Kinematics, in Einstein’s Special Theory, is especially concerned with observers trying to make measurements of the behavior of objects moving in systems relative to themselves. According to Milne’s understanding, these measurements could only be made by the observers signalling among themselves using light or other electromagnetic radiation, using clocks to time the signals. In the end, all measurement—even space and velocity—reduced to timing the signals as they went from one observer to another. This idea of measurement represented a revolutionary simplification of previous ideas, and held philosophical interest for that reason alone. There were practical consequences as well. As Bondi later remarked, “Milne’s idea led straightaway to the radar speed gun!”