A dipole moment of the microwave background as a cosmological effect

We present a spherically symmetrical, Tolman-Bondi cosmological model, in which the curvature of space and the entropy (i. e. , the photon to baryon ratio) varies with a distance from the center. The dipole and quadrupole moments in the distribution of the microwave cosmic background radiation are calculated as a function of cosmic time and position of an observer, assuming that the distance to the horizon is much smaller than any characteristic scale in the model. We find that the quadrupole moment is affected mostly by the gradient in the curvature of space (a gradient in the gravitational potential), while the dipole moment is dominated by the gradient of entropy. It is easy to select the parameters so that the dipole is much larger than quadrupole. This indicates that the observed dipole in the microwave background may be cosmological in origin. The usual interpretation in terms of an infall onto the "Great Attractor, " or another relatively local mass concentration, should not be considered to be the only possibility. In order to reproduce the observed dipole moment the entropy at horizon in the direction toward 11ʰ^ right ascension and -25ᵈeg^ declination should be 0. 8% higher than in the opposite direction. The clearest distinction between a local Doppler effect and a cosmological origin of the observed dipole moment may be provided by the kinematics of galaxies. Conceptually the simplest, but very difficult in practice, would be the observations of proper motions of moderately distant galaxies. There is a possibility of using the effects of gravitational microlensing to estimate proper motions of galaxies. A massive search for type Ia supernovae could provide a verification of the large-scale disturbances in the Hubble flow based on a stellar, rather than a galactic distance indicator.