Entropy of viscous Universe models

The cosmological event horizon entropy and the apparent horizon entropy of the ΛCDM and the Bianchi type I Universe model with viscosity has been calculated numerically, and analytically in the large time limit. It is shown that for these Universe models the cosmological event horizon entropy increases with time and for large times it approaches a finite maximum value. The effect of viscosity upon the entropy is also studied and we have found that its role is to decrease the entropy. The bigger the viscosity coefficient is the less the entropy will be. Furthermore, the radiation entropy for the ΛCDM Universe model with and without viscosity is investigated, and together with the cosmological event horizon entropy are used to examine the validity of the generalized second law of thermodynamics, which states that the total rate of change of entropy of the Universe is never negative, in this Universe model.     

The thermodynamics of early universe

Using the extented Jaynes's principle of maximum entropy we determine the effect of the quantum phenomena on the thermodynamical properties of matter in the early stage of Universe. It is shown that the thermodynamical free energy of the matter of the early Universe becomes very large value due to these quantum phenomena. Both the entropy as well as the free energy of the Universe become singular at the Big Bang.     

The role of expansion for the entropy of the Universe

Under assumption of the closed FRW-universe, the idea is presented that the cosmological expansion/contraction on its own, has an entropy balancing effectively the changing entropy of the cosmic fluid in such a way that at every epoch the total entropy of the Universe remains constant.     

Evolution of the information in the universe

Information in the universe evolves according to a nonlinear law, which results from a combination of nonlinear dynamics and quantum theory. The Kolmogoroff-Sinai entropy rate of the Universe evolves in inverse proportion to the temperature. Since the evolution of temperature is known from standard cosmology, the time dependence of the universal entropy rate can be determined and the temporal evolution of the universal information content can be calculated. Information starts growing at the enormous rate of 10⁴⁴ bits per second from an initial value of at least 2 (seven) bits at Planck time. However, it reaches its contemporary value only if one or more inflationary phases have been passed by the Universe in the course of its evolution.     

The expansive nondecelerative universe

(a) Hubble's discovery of the expansion of the Universe makes it possible to choose unambiguously from the models described by Friedmann's equations of universe dynamics. (b) From the present temperature of the cosmic microwave background radiation, the specific entropy in the matter era and the model properties of the expansive nondecelerative universe, we can determine the present parameters of our Universe with deviations smaller than 2.2%.     

On the exact solutions and invariant rays of the phase plane in Brans-Dicke theory

On the basis of the model properties of the expansive nondecelerative universe, present temperature of cosmic microwave background and specific entropy in the era of matter, the present parameters of our Universe may be exactly determined.     

The signature of string ball near surface horizon of cylindrical Universe

The correspondence principle offered a unique opportunity to test cylindrically symmetric model for Universe at correspondence point “the centre of mass energies around (M _s/(g _s)²)”. First by using this symmetry, the Universe state for highly excited string “string ball” is studied and the entropy of these states is calculated. Then, to consider the string ball states, a copy of the original Hilbert space is constructed with a set of creation/annihilation operators that have the same commutation properties as the original ones. The total Hilbert space is the tensor product of the two spaces H _physical ?H _unphysical , where in this case H _physical denotes the physical quantum state space of the string ball. It is shown that string ball states can be represented by a maximally entangled two-mode squeezed state of the physical and unphysical spaces of string. Also, the entropy for these string states is calculated. It is found that Universe entropy matches the string entropy at transition point. This means that our result is consistent with correspondence principle and thus cylindrically symmetric model works. Finally the signature of bosonic string ball is studied. When string balls are produced, they evaporate to Massive particles like Higgs boson. Then Higgs bosons decay to quarks and gluons. Thus an enhancement of these partons can be a signature of bosonic string ball inside the cylindrically symmetric Universe.     

Oscillatory Universe, dark energy and general relativity

The concept of oscillatory Universe appears to be realistic and buried in the dynamic dark energy equation of state. We explore its evolutionary history under the framework of general relativity. We observe that oscillations do not go unnoticed with such an equation of state and that their effects persist later on in cosmic evolution. The ‘classical’ general relativity seems to retain the past history of oscillatory Universe in the form of increasing scale factor as the classical thermodynamics retains this history in the form of increasing cosmological entropy.     

Trends of stellar entropy along stellar evolution

This paper is devoted to discussing the difference in the thermodynamic entropy budget per baryon in each type of stellar object found in the Universe. We track and discuss the actual decrease of the stored baryonic thermodynamic entropy from the most primitive molecular cloud up to the final fate of matter in black holes, passing through evolved states of matter as found in white dwarfs and neutron stars.We then discuss the case of actual stars with different masses throughout their evolution, clarifying the role of the virial equilibrium condition for the decrease in entropy and related issues. Finally, we discuss the role of gravity in driving the composition and the structural changes of stars with different Main Sequence masses during their evolution up to the final product. Particularly, we discuss the entropy of a black hole in this context arguing that the dramatic increase in its entropy, differently from the other cases, is due to the gravitational field itself.     

Natural entropy production in an inflationary model for a polarized vacuum

Though entropy production is forbidden in standard FRW Cosmology, Berman and Som presented a simple inflationary model where entropy production by bulk viscosity, during standard inflation without ad hoc pressure terms can be accommodated with Robertson–Walker’s metric, so the requirement that the early Universe be anisotropic is not essential in order to have entropy growth during inflationary phase, as we show. Entropy also grows due to shear viscosity, for the anisotropic case. The intrinsically inflationary metric that we propose can be thought of as defining a polarized vacuum, and leads directly to the desired effects without the need of introducing extra pressure terms.     

A note on the problem of choosing a model of the Universe,IV

The Friedmannian model of the Universe with ultra-relativistic equation of statep=–1/3 withk=0 is nondecelerative, i.e., it expands with the constant velocityv=c during the whole expanding phase of evolution of the Universe. The ultrastable nondecelerative model is the only model of the Universe which fulfills all conditions resulting from the quantum-mechanical and relativistic analysis of the Universe.     

The phase diagram of the intergalactic medium and the entropy floor of groups and clusters: are clusters born warm?

We point out that two problems of observational cosmology, namely the facts (i) that ≳60 per cent of the baryonic content of the Universe is not observed at   z ∼ 0  and (ii) that the properties of small clusters do not agree with simple expectations, could be closely related. As shown by recent studies, the shock heating associated with the formation of large-scale structures heats the intergalactic medium (IGM) and leads to a 'warm IGM' component for the gas. In the same spirit, we suggest the intracluster medium (ICM) to be a mixture of galaxy-recycled, metal-enriched gas and intergalactic gas, shock heated by the collapsing much larger scales. This could be obtained through two processes: (1) the late infalling gas from the external warm IGM is efficiently mixed within the halo and brings some additional entropy, or (2) the shocks generated by larger non-linear scales are also present within clusters and can heat the ICM. We show that, if assumption (1) holds, the entropy brought by the warm IGM is sufficient to explain the observed properties of clusters, in particular the entropy floor and the   L _X– T   relation. On the other hand, we note briefly that scenario (2) would require a stronger shock heating because of the larger density of the ICM as compared with filaments. Although the efficiency of these two processes remains to be checked on a quantitative level, they have the advantage of dispensing with the need to invoke any strong preheating from supernovae or quasars (which has otherwise been introduced for the sole purpose of reproducing the behaviour of clusters). Matter ejection by galaxies is included in the present calculations and, consistently with the metal-enrichment requirements, is indeed shown to yield only a quite moderate entropy increase. Our scenario of clusters being 'born warm' can be checked through the predicted redshift evolution of the entropy floor.     

On the nature of dark energy: the lattice Universe

There is something unknown in the cosmos. Something big. Which causes the acceleration of the Universe expansion, that is perhaps the most surprising and unexpected discovery of the last decades, and thus represents one of the most pressing mysteries of the Universe. The current standard ΛCDM model uses two unknown entities to make everything fit: dark energy and dark matter, which together would constitute more than 95 % of the energy density of the Universe. A bit like saying that we have understood almost nothing, but without openly admitting it. Here we start from the recent theoretical results that come from the extension of general relativity to antimatter, through CPT symmetry. This theory predicts a mutual gravitational repulsion between matter and antimatter. Our basic assumption is that the Universe contains equal amounts of matter and antimatter, with antimatter possibly located in cosmic voids, as discussed in previous works. From this scenario we develop a simple cosmological model, from whose equations we derive the first results. While the existence of the elusive dark energy is completely replaced by gravitational repulsion, the presence of dark matter is not excluded, but not strictly required, as most of the related phenomena can also be ascribed to repulsive-gravity effects. With a matter energy density ranging from ～5 % (baryonic matter alone, and as much antimatter) to ～25 % of the so-called critical density, the present age of the Universe varies between about 13 and 15 Gyr. The SN Ia test is successfully passed, with residuals comparable with those of the ΛCDM model in the observed redshift range, but with a clear prediction for fainter SNe at higher z. Moreover, this model has neither horizon nor coincidence problems, and no initial singularity is requested. In conclusion, we have replaced all the tough problems of the current standard cosmology (including the matter-antimatter asymmetry) with only one question: is the gravitational interaction between matter and antimatter really repulsive as predicted by the theory and as the observation of the Universe seems to suggest? We are awaiting experimental responses.     

Probing the dark side of the Universe with weak gravitational lensing effects

Arising from gravitational deflections of light rays by large-scale structures in the Universe, weak-lensing effects have been recognized as one of the most important probes in cosmological studies. In this paper, we review the main progress in weak-lensing analyses, and discuss the challenges in future investigations aiming to understand the dark side of the Universe with unprecedented precisions.     

Energy Composition of the Universe: Time-Independent Internal Symmetry

The energy composition of the Universe, as emerged from the Type Ia supernova observations and the WMAP data, looks preposterously complex, – but only at the first glance. In fact, its structure proves to be simple and regular. An analysis in terms of the Friedmann integral enables to recognize a remarkably simple time-independent covariant robust recipe of the cosmic mix: the numerical values of the Friedmann integral for vacuum, dark matter, baryons and radiation are approximately identical. The identity may be treated as a symmetry relation that unifies cosmic energies into a regular set, a quartet, with the Friedmann integral as its common genuine time-independent physical parameter. Such cosmic internal (non-geometrical) symmetry exists whenever cosmic energies themselves exist in nature. It is most natural for a finite Universe suggested by the WMAP data. A link to fundamental theory may be found under the assumption about a special significance of the electroweak energy scale in both particle physics and cosmology. A freeze-out model developed on this basis demonstrates that the physical nature of new symmetry might be due to the interplay between electroweak physics and gravity at the cosmic age of a few picoseconds. The big ‘hierarchy number’ of particle physics represents the interplay in the model. This number quantifies the Friedmann integral and gives also a measure to some other basic cosmological figures and phenomena associated with new symmetry. In this way, cosmic internal symmetry provides a common ground for better understanding of old and recent problems that otherwise seem unrelated; the coincidence of the observed cosmic densities, the flatness of the co-moving space, the initial perturbations and their amplitude, the cosmic entropy are among them.     

Dark matter annihilation at cosmological redshifts: possible relic signal from annihilation of weakly interacting massive particles

We discuss the possibility of observing the products of the dark matter annihilation that was going on in the early Universe. Of all the particles that could be generated by this process, we consider only photons, as they are both uncharged and easily detectable. The younger the Universe was, the higher the dark matter concentration n and the annihilation rate (proportional to n ²) were. However, the emission from the very early Universe cannot reach us because of the opacity. The main part of the signal was generated at the moment the Universe had just become transparent for the photons produced by the annihilation. Thus, the dark matter annihilation in the early Universe should have created a sort of relic emission. We obtain its flux and the spectrum.
If weakly interacting massive particles (WIMPs) constitute dark matter, it is shown that we may expect an extragalactic gamma-ray signal in the energy range 0.5–20 MeV with a maximum near 8 MeV. We show that an experimentally observed excess in the gamma-ray background at 0.5–20 MeV could be created by the relic signal from the annihilation of WIMPs only if the dark matter structures in the Universe had appeared before the Universe became transparent for the annihilation products  ( z ≃ 300)  . We discuss in more detail physical conditions whereby this interpretation could be possible.     

Entropy change and phase transitions in an expanding Universe

The work compiles a correlated study of a gravitational quasi equilibrium thermodynamic approach for establishing and signifying a unique behavior of the cosmological entropy and phase transitions in an expanding Universe. On the basis of prescribed boundary conditions for the cluster temperature a relation for the intra‐cluster medium (ICM) of galaxy clusters has been derived. A more productive and signifying approach of the correlation functions used for galaxy clustering phenomena shows a unique behavior of the entropy change where a phenomenon known as the gravitational phase transition occurs. This unique behavior occurs with a symmetry breaking from mild clustering to low clustering and from mild clustering to high clustering which differs from a normal symmetry breaking in material sciences. We also derive results for the specific latent heat associated with the phase transitions of 3.20 T_c and 0.55 T_c for the mildly clustered phase to the low clustered phase and from the mildly clustered phase to the highly clustered phase, respectively. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Size of ambiplasma domains in the Universe

Assuming that the initial state of the Universe can be simulated by a thin large-scale homogeneous ambiplasma described by fluid type equations for charged particles (both matter and antimatter particles), stability calculations have been carried out of the various normal modes which might be supported by such a system. The present simplified analysis does not lead to the formation of matter-antimatter symmetric domains smaller than the size of the proto-metagalaxy (Alfvén, 1981) from the initial state of the Universe.     

Acceleration of the Universe in presence of tachyonic field

In this letter, we have assumed that the Universe is filled in tachyonic field with potential, which gives the acceleration of the Universe. For certain choice of potential, we have found the exact solutions of the field equations. We have shown the decaying nature of potential. From recently developed statefinder parameters, we have investigated the role of tachyonic field in different stages of the evolution of the Universe.     

The formation of the spectrum of preglactic inhomogeneities in the CDM and HDM of the Universe

We consider the evolution of large-scale cosmological density perturbations in CDM and HDM Universe containing weakly interacting relativistic particles with number density to be the model free paramer. The dependence of parameters of the large-scale structure on the collisionless particle numbers is discussed. A new cosmological test of the total number of light weakly interacting particles in the Universe is proposed.