NEW IDEAS IN COSMOLOGY AND ASTROPHYSICS From 26 to 28 June 1961 a conference on extragalactic astronomy and cosmology was convened in Moscow under the auspices of the Cosmogony Commission of the Astronomical Council of the USSR Academy of Sciences. The conference was organized as a preparation for the symposium on these subjects which was to be held (in the USA) at the forthcoming Eleventh Congress of the International Astronomical Union in September 1961. Many prominent Soviet scientists participated in the conference and some very interesting reports were presented.
The main problems related to extragalactic research during recent years were considered in the comprehensive report of V. A. Ambartsumyan (Byurakan Astrophysical Observatory).
B. A. Vorontsov-Vel'yaminov (GAISh) concentrated in his report upon interacting galaxies and the physical interpretation of the observed galactic interactions.
The distances, motions, and distributions of galaxies within a sphere with a radius of 15 megaparsecs were discussed by Yu. P. Pskovskii (GAISh). He indicated that the complex of galaxies located within a sphere of radius 10 megaparsecs around our Galaxy is in a state of isotropic expansion associated with a rotation about some center lying in the constel lation Virgo. A comparison of the distribution of galaxies and the nature of their motions makes it possible to specify the approximate pattern of galactic motions in our part of the Metagalaxy.
E. A. Dibai (GAISh) suggested that the asymmetric distribution of gas and dust in the spiral galaxies be interpreted as a result of the combined action of rotation and radial motion along the arms. A comparison between the results obtained from this analysis and the observational data indicates that the spirals become twisted during the evolution of the spiral galaxies. • The joint report of Ya. A. Smorodinskii and B. M. Pontecorvo (Joint Institute for Nuclear Research at Dubna) was received with great interest. This report dealt with the possible role of neutrinos in astrophysics and cosmology. The two authors presented strong arguments in favor of the existence of a considerable neutrino-antineutrino background in the universe. In the present epoch the energy of the background particles
may be very low, as a result of an adiabatic reduction of the energy during the expansion of our part of the universe. During earlier evolutionary stages, however, the energy possessed by neutrinos may have been many orders of magnitude higher than the energy density of heavy matter. According to the available data, it is possible that even now the energy density of neutrinos in the universe is comparable to that of nucleons, and that it is many times greater than the energy density of visible radiation. Consequently, neutrinos must play a significant part in determining the geometry of the world. During previous stages in the evolution of the universe, isotropically and uniformly distributed neutrinos may well have completely determined the space-time metric*.
D. A. Frank-Kamenetskii (Atomic Energy Institute of the USSR Academy of Sciences), in developing his theory of the spontaneous instability of a vacuum, considered the hypothesis of the multiple production of nucleon pairs. This hypothesis is a modern variant of Boltzmann's fluctuation hypothesis. The gist of Frank-Kamenetskii's hypothesis is as follows.
The universe is assumed to be an infinite expanse which is essentially flat and free of matter. Somewhere in it, immense fluctuations of the vacuum take place very infrequently, accompanied by the formation of a colossal mass of neutrons and antineutrons. The presence of this mass causes a local twisting of space, which in turn leads to a local expansion of space. During this expansion, particles and antiparticles are annihilated and radiation is emitted. Turbulent motions arise, and eddies having unimaginably vast dimensions are formed. At a point in space where a neutron excess is accidentally created, a world similar to ours comes into existence (that is, a large accumulation of galaxies). In the event of an excess of antiparticles, on the other hand, an "antiworld" is created. The probability of such a fluctuation of the vacuum may turn out to be very low, but it will nevertheless not be zero.