Galaxies formed first, at redshifts of 2 to 4—or roughly nine to twelve billion years ago. Then those galaxies gathered into clusters, at redshifts of less than 1—or less than roughly six billion years ago. And now, today (in a cosmic sense), those clusters are gathering into superclusters. Matter clumped first in small structures, and those small structures continued to gather together. The universe has apparently had a bottom-up, simple-to-complex
