  The theoretical basis for the prediction of anisotropies in the cosmic
microwave background is very well developed. Very low amplitude density and
temperature perturbations produce small gravitational effects, leading to an
anisotropy that is a combination of temperature fluctuations at the surface of
last scattering and gravitational redshifts both at last scattering and along
the path to the observer. All of the primary anisotropy can be handled by
linear perturbation theory, which allows a very accurate calculation of the
predicted anisotropy from different models of the Universe.
