 Earlier measurements of the CMB indicated that it was homogeneous. That would be a problem, because if it were 100% homogeneous, the resulting universe would be 100% homogeneous, and it isn't. But our measurement technologies have improved dramatically over the past half century. The Planck satellite measurements detected small amounts of temperature deviation, called anisotropy, meaning different in different directions. The image uses color to show variations from the average with blue for minus 200 millionths of a degree through green and yellow to red, which represents plus 200 millionths of a degree. That temperature deviation comes to one part in 100,000. These temperature deviations come from small mass density deviations in the plasma at the time of decoupling. For example, suppose we had a small mass density excess in this region. Light from this region would be gravitationally redshifted. These mass density deviations would be the same magnitude as the temperature deviations, one in 100,000. It is also important to note that these anisotropies have structure. We see large structures, small, even tiny structures, and giant structures. We even see structures within structures at every scale. In other words, they're quite fractal. These small-scale anisotropies in the CMB are what led to the large-scale structures such as galaxy clusters, filaments, and voids that we see today. For example, a very tiny spot of red on the surface of last scattering, representing a small decrease in mass density in that region, will have expanded 1,100 times to the size of the coma cluster today. The fact that there is a cosmic microwave background with all these characteristics is one of the most important pieces of evidence we have that verifies and validates our current Big Bang model of the universe.