In the s

Andrei Doroshkevich is a Leading Research Scientist at the Astro Space Center, the P. N. Lebedev Physical Institute of the Russian Academy of Sciences, Moscow. His research interests include cosmology, galaxy formation, and the relic radiation background.

For cosmology the 1960s were a very active period. Over these years the rapid development of observational techniques offered many discoveries, including the relic radiation (the CMBR), X-ray sources, and quasars. At the same time significant progress had been achieved in the understanding and description of the nature of black holes. These discoveries have demonstrated the complex nature of the universe composed of a set of objects with a wide variety of properties and evolutionary histories.

This progress immediately rearranged cosmology and transformed it to the physical theory focused on the interpretation of new phenomena and the construction of corresponding physical models. These models have opened up new fields of application for classical and quantum physics in exotic situations such as the early stages of the evolution of the universe and objects with superstrong pressure, magnetic and gravitational fields. Theoretical analysis of such problems had begun already in earlier publications of Landau, Oppenheimer, Volkoff, Snyder, Tolman, Gamow, Alpher, Herman, and some others. However, only at this period did the application of abstract theoretical constructions to observed objects become possible.

For cosmology as a whole the discovery of the CMBR was most important. In this context the key role must go to G. Gamow, who formulated the hypothesis of the hot universe using very limited observational estimates of the chemical composition of old stars. Unfortunately his expectations of the direct observations of the CMBR were not so promising and they were not realized over an extended period after his predictions.

The development of Soviet cosmology at this period is well reviewed here by I. Novikov. I can only repeat that in 1963-1964 Novikov and I began to work in Zel'dovich's group and were interested in manifestations of the properties of galaxies. Thus, we calculated the background radiation produced by galaxies and found that it is quite small in the millimeter wavelength range. (It is interesting that this inference remains valid up to now.) For comparison we plotted in the same figure the Planck spectrum of the relic radiation for the temperature T = 1K. From this figure it was obvious that the CMBR can be successfully observed by high precision measurements at suitable wavelengths. The main problems were linked with the technical limitations and reduction of atmospheric noise. Unfortunately, owing to very limited contacts between Soviet and Western astronomers, our publication (Doroshkevich and Novikov 1964) remained unknown for many years.

In the 1960s the very limited available information about the discovered phenomena stimulated construction of a wide set of cosmological models, the majority of which are forgotten now. Nonetheless, some of such models can be restored in the light of the new observational evidence in favor of weak large-scale anisotropy of the universe. Of course, such models must be close in main features to the now accepted ACDM cosmology which quite well describes the main observations. Beyond that point, according to presently discussed simple models of cosmological inflation, the primordial anisotropy, global rotation and magnetic field catastrophically decayed. This means that there are problems that call for further observational and theoretical investigations.

However, the list of the parameters used for the analysis of the intensity and polarization of the CMBR can be extended and, for example, include the possible contribution of small-scale initial entropy perturbations and possible complex composition of the dark matter component. Such analysis strongly restrict amplitudes of these "hidden parameters" but cannot reject them. At the same time, it can noticeably change the derived parameters of the ACDM cosmological model.

These comments are called on to demonstrate a succession of many basic ideas in cosmology which have been discussed in the sixties and remain relevant up to now.

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