Observational evidence from the Cosmic Microwave Background (CMB) confirms the existence of initial density fluctuations in the early universe, which are the seeds for galaxy formation.

The Cosmic Microwave Background (CMB) is the faint afterglow of the Big Bang, a snapshot of the universe when it was only about 380,000 years old. Precise measurements of the CMB by missions like COBE, WMAP, and Planck have revealed tiny temperature anisotropies – minuscule variations in temperature across the sky. These variations correspond to slight differences in density in the primordial plasma. These initial density fluctuations, though small, were crucial. Over billions of years, gravity acted upon these slightly denser regions, pulling in more matter. The regions that were slightly denser became the gravitational wells where dark matter began to clump, eventually leading to the formation of the first stars, galaxies, and the large-scale structure of the cosmos we observe today. The amplitude and distribution of these fluctuations are key inputs for cosmological models predicting galaxy formation.