What evidence supports the existence of fluctuations in the cosmic microwave background?

The presence of fluctuations in the cosmic microwave background (CMB) is supported primarily by the evidence from large scale structure formation in the universe. The CMB, which is the remnant radiation from the Big Bang, contains tiny temperature fluctuations caused by density variations in the early universe.

These fluctuations are critical because they correspond to regions of slightly different densities. Over time, these density variations served as the seeds for the gravitational collapse that led to the formation of galaxies and clusters of galaxies. As the universe expanded, regions with higher density attracted more matter, leading to the large-scale structure we observe today, including galaxy clusters, filaments, and voids.

The correlation between the observed CMB fluctuations and the distribution of galaxies across the universe provides strong observational data supporting the theory of cosmic inflation and the evolution of structure in the universe. These connections allow astronomers to understand how initial conditions in the early universe led to the cosmic web structure that we see in the present day.