Direct observation of structure in the cosmic microwave background

Temperature fluctuations in the cosmic microwave background are a key prediction of cosmological models of structure formation in the early Universe. Ground-based multi-frequency radio observations of the microwave background reveal well defined features that are not of atmospheric or Galactic origin; instead, they delineate the primordial density perturbations from which the structure in the present Universe originated. The amplitude of these perturbations confirms the earlier statistical detection by the COBE satellite.