What did the near-perfect proportionality Hubble plotted imply about galactic motion?

It implied a universal rule that the rate of recession is proportional to the distance, defining the expansion of space itself.

The striking, near-perfect proportionality observed when plotting recessional velocity against distance revealed that galactic motion was not random scatter but followed a universal rule. This relationship proved that the rate of recession scaled linearly with how far away an object was. This uniformity across the sky suggested a profound physical reality: the expansion was not galaxies rushing outward through static space from a center, but rather the metric of space itself stretching uniformly everywhere. This proportionality is the core definition of cosmic expansion, distinguishing it from potential chaotic motion.