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This paper appeared in Russian in Doklady AN SSSR and in English in the translation journal Soviet Physics–Doklady. In it the cosmic radiation from galaxies in the frequency range $$10^8 \hbox {Hz}$$ to $$10^{15} \hbox {Hz}$$ was estimated and shown to agree with data. It was then shown, following earlier ideas of Gamow, that the black-body cosmic microwave background from a big bang would significantly exceed the galactic radiation in the range $$10^9 \hbox {Hz}$$ to $$10^{11} \hbox {Hz}$$ . This was the first accurate prediction of that background, which now plays a key role in cosmology. The first announcement of its detection came in the following year. The paper has been selected by the Editors of General Relativity and Gravitation for re-publication in the Golden Oldies series of the journal. This republication is accompanied by an editorial note written by R. Durrer and a brief autobiography by A. G. Doroshkevich: an autobiography of I. D. Novikov appeared with a previous Golden Oldie.

We study the effects of an information-theoretically motivated nonlinear correction to the Wheeler-deWitt equation in the minisuperspace scheme for flat, $k=0$, Friedmann-Robertson-Walker (FRW) universes. When the only matter is a cosmological constant, the nonlinearity can provide a barrier that screens the original Big Bang, leading to the quantum creation of a universe through tunneling just as in the $k=1$ case. When the matter is instead a free massless scalar field, the nonlinearity can again prevent a contracting classical universe from reaching zero size by creating a bounce. Our studies here are self-consistent to leading order in perturbation theory for the nonlinear effects., Final Journal version: Further clarification in Introduction and Conclusion. references added. figures same as in version 1

A brief overview of loop quantum cosmology of homogeneous isotropic models is presented with emphasis on the origin of and subtleties associated with the resolution of big bang and big crunch singularities. These results bear out the remarkable intuition that John Wheeler had. Discussion is organized at two levels. The the main text provides a bird's eye view of the subject that should be accessible to non-experts. Appendices address conceptual and technical issues that are often raised by experts in loop quantum gravity and string theory., To appear in the Proceedings of the Bad Honef Workshop entitled \emph{Quantum Gravity: Challenges and Perspectives}, dedicated to the memory of John A. Wheeler

Recent observations of large scale structure of the Universe, especially that of Type Ia supernovae, indicate that the Universe is flat and is accelerating, and that the dominant energy density in the Universe is the cosmic dark energy. We propose a model in which the cosmic effective Yang-Mills condensate familiar in particle physics plays the role of the dark energy that causes the acceleration of the Universe. Since the quantum effective Yang-Mills field in certain states has the equation of state py = −ρy, when employed as the cosmic matter source, it naturally results in an accelerating expansion of the Universe. With the matter components (Ωm ∼ 1/3) being added into the model, the composition of YM condensate and matter components can give rise to the desired equation of state w ∼ −2/3 for the Universe.

Much of the published work regarding the Isotropic Singularity is performed under the assumption that the matter source for the cosmological model is a barotropic perfect fluid, or even a perfect fluid with a $\gamma$-law equation of state. There are, however, some general properties of cosmological models which admit an Isotropic Singularity, irrespective of the matter source. In particular, we show that the Isotropic Singularity is a point-like singularity and that vacuum space-times cannot admit an Isotropic Singularity. The relationships between the Isotropic Singularity, and the energy conditions, and the Hubble parameter is explored. A review of work by the authors, regarding the Isotropic Singularity, is presented., Comment: 18 pages, 1 figure

The Hamilton-Jacobi equation for the string cosmology is solved using the gradient expansion method. The zeroth order solution is taken to be the standard pre-big bang model and the second order solution is found for the dilaton and the three-metric. It indicates that corrections generated by inhomogeneities of the seed metric are suppressed near the singularity and are growing towards the asymptotic past, but corrections generated by the dilaton inhomogeneities are growing near the singularity and are suppressed in the past. Possible influences of initial metric inhomogeneities on the pre-big bang superinflation are discussed., Comment: Strongly revised version

Recently Melia and Shevchuk (Mon Not R Astron Soc 419:2579,2012) (MS) have proposed the so-called \(R_h =ct\) cosmology where the “Gravitational Horizon” of the universe \(R_h\) is equal to the distance travelled by light since “Big Bang”. Here we would like to see whether the basic claim \(R_h=ct\) is correct or not because MS have not given any cogent derivation for the same. Essentially we will compare the twin expressions for the Einstein energy momentum complex (EMC) of the Friedmann universe obtained by using an appropriate superpotential and also by a direct method. To enable a meaningful comparison of the twin expressions, both are computed by using the same quasi-Cartesian coordinates. We however do not claim that Einstein EMC is superior to many other routes of defining EM of a self-gravitating system. In fact, for static isolated spherical syatems, the idea of a coordinate independent field energy of Lynden-Bell and Katz (Mon Not R Astron Soc 213:21, 1985) might be quite physically significant. Yet, here, we use Einstein EMC because (i) our system is non-static and not isolated one (ii) our primary aim is not find any absolute value of EM, and, finally, (iii) only Einstein pseudo-tensor offers equivalent twin expressions for EM which one can be equated irrespective of any physical significance. Following such comparison of equivalent twin expressions of Einstein energy, we find an exact proof as to why Friedmann universe must be spatially flat even though, mathematically one can conceive of curved spaces in any dimension. Additionally, it follows that, apparently, the scale factor \(S(t) \propto t\) as insisted by \(R_h=ct\) proposition. Nonetheless, because of close similarity of this form, \(S(t) \propto t\), with the (vacuum) Milne metric, and also because of implied unphysical equation of state, \(R_h=ct\) cosmology is unlikely to represent the physical universe.

We present the result of an experiment of the Florence group which has detected a quadrupole anisotropy in the cosmic background radiation. We show that this result implies that the universe either has large metric perturbations outside the particle horizon, or will become largely irregular in the future.

Mechanics is considered in a universe containing negative mass. Demanding (i) conservation of momentum, (ii) principle of equivalence, (iii) no runaway motions, (iv) no Schwarzschild black holes, and (v) the inertial and active gravitational masses of a body shall have the same sign, we find thatall mass must be negative. Some properties of such a universe are investigated. We show that a neutral spherical body of arbitrarily small size is possible, and observers external to it can communicate with each other by light rays without horizon problems. There are no cosmological models with a power-law big bang, and there is an abundance of nonsingular models. Like electric charges would attract each other, and unlike ones would repel. This could produce stars and galaxies held together by charge and not gravity. The investigation does not suggest any reason why mass in the real universe should be positive.

If one defines the size of the present universe in terms of a hypersurface of simultaneity generated by the spatial geodesies orthogonal to our world line today, then it is finite in all expanding Big Bang Friedmann models.