Final answer:
The smoothness of the CMBR was a problem because it seemed too uniform to allow for the formation of galaxies and structures, but inflation theory and precise measurements reveal minute fluctuations that explain structure formation.
Step-by-step explanation:
The observation that the cosmic microwave background radiation (CMBR) is very smooth was initially puzzling because the formation of structures such as galaxies requires inhomogeneities in the early universe. These inhomogeneities—or wrinkles—are represented by variations in temperature and density that would later evolve into the large-scale structures seen today. The Big Bang model predicts that such fluctuations should exist, but the CMBR appeared to be too uniform. This led to the horizon problem, questioning how regions of the universe now seen to be similar in temperature could have been in causal contact. The theory of inflation addresses this by positing a rapid expansion of space that smoothed out any initial irregularities, leaving the CMBR extremely smooth with tiny fluctuations that are only observable with precise measurements. These tiny fluctuations are the seeds around which galaxies and other structures formed. Therefore, while the CMBR is not perfectly smooth, its extreme smoothness, coupled with the minute variations, is in line with current cosmological theories.