The nature and origin of large-scale density fluctuations

The small-scale clumpiness of the universe is studied in the light of the discovery of large angular scale fluctuations in the brightness of the microwave background. The constraints that this new measure may provide on models for the nature and origin of the departures from a homogeneous universe are reviewed. The possibility that the anisotropy originates in the Galaxy, that it is primeval, or that it arises from gravitational potential gradients is assessed and the relationship of the anisotropy to the Sachs-Wolfe effect is examined. The relation between the actual galaxy distribution and the measure of it by n-point correlation functions is discussed in order to determine whether the adopted covariance function is correct. Anticorrelation and models for the origin of clustering, as well as the clustering length problem are also investigated.