What conceptual leap cemented Hubble's contribution regarding light shifting?

Realizing the uniformity pointed toward the space *between* galaxies stretching, rather than galaxies moving *through* static space.

While Vesto Slipher provided the velocity data (redshifts), Hubble's genius lay in synthesizing this with distance measurements to prove the cosmological nature of the redshift. If the universe were static, redshift would imply local gravitational interactions or random motion. Hubble's conceptual leap was recognizing that the observed *uniformity* of the velocity-distance relationship across the entire sky meant that the spatial fabric itself was expanding—carrying the light waves with it. This crucial distinction between motion *through* fixed space and the expansion *of* space cemented his contribution to modern cosmology.