Cosmological Model in Four Time and Four Space Dimensions

We develop a cosmological model in a physical background scenario of four time and four space dimensions ((4+4)-dimensions or (4+4)-universe). We show that in this framework the (1+3)-universe is deeply connected with the (3+1)-universe. We argue that this means that in the (4+4)-universe there exists a duality relation between the (1+3)-universe and the (3+1)-universe.

Applying the Stefan-Boltzmann Law to a Cosmological Model (a Brief Note)

This brief note brings the reader up-to-date with the recent successes of the new Haug-Tatum cosmology model. In particular, the significance of recent proof that the Stefan-Boltzmann law applies to such a model is emphasized and a rationale for this is given. Remarkably, the proposed solutions of this model have incorporated all 580 supernova redshifts in the Union2 database. Therefore, one can usefully apply this thermodynamic law in the form of a continually expanding black-body universe model. To our knowledge, no other cosmological model has achieved such high-precision observational correlation.

Cosmological Constant and Stability of the Cosmological Models

The importance of cosmological constant for the cosmological models is given. The variations of the cosmological model for parameters and were discussed respectively. Near , the cosmological model is unstable with the change of , and near , the cosmological model is unstable with the change of . So when we consider the stable cosmological model, we must consider the nonzero cosmological constant.

Bianchi-Type II String Cosmological Models with Bulk Viscosity

The locally rotationally symmetric Bianchi-type II string cosmological models with bulk viscosity are obtained, where an equation of state, , and a relation between metric potentials, , are adopted. The physical features of the models are also discussed. In special cases the model reduces to the string models without viscosity that was previously given in the literatures.

Anisotropic Plane Symmetric Two-Fluid Cosmological Model with Time-Varying G and A

We investigate a two-fluid anisotropic plane symmetric cosmological model with variable gravitational constant G（t） and cosmological term A（t）. In the two-fluid model, one fluid is chosen to be that of the radiation field modeling the cosmic microwave background and the other one a perfect fluid modeling the material content of the universe. Exact solutions of the field equations are obtained by using a special form for the average scale factor which corresponds to a specific time-varying deceleration parameter. The model obtained presents a cosmological scenario which describes an early acceleration and late-time deceleration. The gravitation constant increases with the cosmic time whereas the cosmological term decreases and asymptotically tends to zero. The physical and kinematical behaviors of the associated fluid parameters are discussed.

Anisotropic Standard Decelerating Cosmological Model with Quadratic Equation of State

Spatially homogeneous and anisotropic Bianchi type-I cosmological model containing perfect fluid with quadratic equation of state has been diagnosed in general theory of relativity. To obtain a deterministic solution, we have used a relation between metric potentials. The exact solution of Einstein’s field equations thus obtained represents an expanding and decelerating universe. The physical and kinematical parameters of the model have also been analyzed with certain constrained between the parameters of the quadratic equation of state.

An interacting two-fluid scenario for dark energy in a Bianchi type-I cosmological model

We study the evolution of the dark energy parameter within a Bianchi type-I cosmological model filled with barotropic fluid and dark energy. The solutions have been obtained for power law and exponential forms of the expansion parameter （they correspond to a constant deceleration parameter in general relativity）. After a long time, the models tend to be isotropic under certain conditions.

A Solution to the Cosmological Constant Problem Using the Holographic Principle (A Brief Note)

This paper integrates a quantum conception of the Planck epoch early universe with FSC model formulae and the holographic principle, to offer a reasonable explanation and solution of the cosmological constant problem. Such a solution does not appear to be achievable in cosmological models which do not integrate black hole formulae with quantum formulae such as the Stephan-Boltzmann law. As demonstrated herein, assuming a constant value of Lambda over the great span of cosmic time appears to have been a mistake. It appears that Einstein’s assumption of a constant, in terms of vacuum energy density, was not only a mistake for a statically-balanced universe, but also a mistake for a dynamically-expanding universe.

Entropy and Cosmological Constant of a Universe Calculated by Means of Dimensional Analysis, Margolus-Levitin Theorem and Landauer’s Principle

By means of the dimensional analysis a spherically simmetric universe with a mass M = c3/(2HG) and radius equal to c/H is considered, where H is the Hubble constant, c the speed of light and G the Newton gravitational constant. The density corresponding to this mass is equal to the critical density ρcr = 3H2/(8πG). This universe evolves according to a Bondi-Gold-Hoyle scenario, with continuous creation of matter at a rate such to maintain, during the expansion, the density always critical density. Using the Margolus-Levitin theorem and the Landauer’s principle, an entropy is associated with this universe, obtaining a formula having the same structure as the Bekenstein-Hawking formula of the entropy of a black hole. Furthermore, a time-dependent cosmological constant Λ, function of the Hubble constant and the speed of light, is proposed.

The “Dead Universe” Theory: Natural Separation of Galaxies Driven by the Remnants of a Supermassive Dead Universe

This article explores the dead universe theory as a novel interpretation for the origin and evolution of the universe, suggesting that our cosmos may have originated from the remnants of a preceding universe. This perspective challenges the conventional Big Bang theory, particularly concerning dark matter, the expansion of the universe, and the interpretation of phenomena such as gravitational waves.

The Hawking Hubble Temperature as the Minimum Temperature, the Planck Temperature as the Maximum Temperature, and the CMB Temperature as Their Geometric Mean Temperature

Using a rigorous mathematical approach, we demonstrate how the Cosmic Microwave Background (CMB) temperature could simply be a form of geometric mean temperature between the minimum time-dependent Hawking Hubble temperature and the maximum Planck temperature of the expanding universe over the course of cosmic time. This mathematical discovery suggests a re-consideration of Rh=ctcosmological models, including black hole cosmological models, even if it possibly could also be consistent with the Λ-CDM model. Most importantly, this paper contributes to the growing literature in the past year asserting a tightly constrained mathematical relationship between the CMB temperature, the Hubble constant, and other global parameters of the Hubble sphere. Our approach suggests a solid theoretical framework for predicting and understanding the CMB temperature rather than solely observing it.1.

Black Hole Complementarity in Terms of the Outsider and Insider Perspectives

A complementarity hypothesis concerning outsider and insider perspectives of a gargantuan black hole is proposed. The two thought experiments presented herein are followed by a brief discussion of a new interpretation of black hole interior “space-and-time-reversal”. Specifically, it is proposed that the “singularity” space of the black hole interior is time-like and the expansion time of the black hole interior is space-like. The resemblance of this new insider interpretation to our own expanding and redshifting big bang universe is compelling.

Modelling and Analysis of the Hubble Diagram of 280 Type SNIa Supernovae and Gamma Ray Bursts Redshifts with Analytical and Empirical Redshift/Magnitude Functions

Based on an analysis of 280 Type SNIa supernovae and gamma-ray bursts redshifts in the range of z = 0.0104 - 8.1 the Hubble diagram is shown to follow a strictly exponential slope predicting an exponentially expanding or static universe. At redshifts > 2 - 3 ΛCDM models show a poor agreement with the observed data. Based on the results presented in this paper, the Hubble diagram test does not necessarily support the idea of expansion according to the big-bang concordance model.

Accelerating dark energy models with anisotropic fluid in Bianchi type Ⅵ_0 space-time

Motivated by the increasing evidence for the need of a geometry that re- sembles Bianchi morphology to explain the observed anisotropy in the WMAP data, we have discussed some features of Bianchi type VI0 universes in the presence of a fluid that has an anisotropic equation of state （EoS） parameter in general relativity. We present two accelerating dark energy （DE） models with an anisotropic fluid in Bianchi type VI0 space-time. To ensure a deterministic solution, we choose the scale factor a（t） = √tnet, which yields a time-dependent deceleration parameter, representing a class of models which generate a transition of the universe from the early decelerating phase to the recent accelerating phase. Under suitable conditions, the anisotropic mod- els approach an isotropic scenario. The EoS for DE co is found to be time-dependent and its existing range for derived models is in good agreement with data from recent observations of type Ia supernovae （SNe Ia） （Knop et al. 2003）, SNe Ia data com- bined with cosmic microwave background （CMB） anisotropy and galaxy clustering statistics （Tegmark et al. 2004a）, as well as the latest combination of cosmological datasets coming from CMB anisotropies, luminosity distances of high redshift SNe Ia and galaxy clustering. For different values of n, we can generate a class of physically viable DE models. The cosmological constant A is found to be a positive decreasing function of time and it approaches a small positive value at late time （i.e. the present epoch）, which is corroborated by results from recent SN Ia observations. We also ob- serve that our solutions are stable. The physical and geometric aspects of both models are also discussed in detail.

Stability Analysis of the Viscous Polytropic Dark Energy Model in Einstein Cosmology

The viscous polytropic gas model as one model of dark energy is hot-spot and keystone to the modern cosmology. We study the evolution of the viscous polytropic dark energy model interacting with the dark matter in the Einstein cosmology. Setting the autonomous dynamical system for the interacting viscous polytropic dark energy with dark matter and using the phase space analysis method to investigate the dynamical evolution and its critical stability, we find that the viscosity property of the dark energy creates a benefit for the stable critical dynamical evolution of the interaction model between dark matter and dark energy in the flat Friedmann-Robertson-Walker universe and the viscosity of dark energy will soften the coincidence problem just like the interacting dark energy model.

Dynamical Study of a Constant Viscous Dark Energy Model in Classical and Loop Quantum Cosmology

Dynamical behaviors and stability properties of a flat space Friedmann-Robertson-Walker universe filled with pressureless dark matter and viscous dark energy are studied in the context of standard classical and loop quantum cosmology. Assuming that the dark energy has a constant bulk viscosity, it is found that the bulk viscosity effects influence only the quintessence model case leading to the existence of a viscous late time attractor solution of de- Sitter type, whereas the quantum geometry effects influence the phantom model case where the big rip singularity is removed. Moreover, our results of the Hubble parameter as a function of the redshift are in good agreement with the more recent data.

Constraining the variable generalized Chaplygin gas model in matter creation cosmology

We explore the variable generalized Chaplygin gas(VGCG)model in the theory of matter creation cosmology within the framework of a spatially homogeneous and isotropic flat Friedmann—Lemai tre—Robertson—Walker space-time.Matter creation cosmology is based on reinterpretation of the energy–momentum tensor in Einstein's field equations.This creation corresponds to an irreversible energy flow from the gravitational field to the created matter constituents.The variable Chaplygin gas(VCG)is also studied as a particular solution.We use the Markov chain Monte Carlo method to constrain the free parameters of three models,namely,Lambda-Cold-Dark matter(ΛCDM),VGCG and VCG models with and without matter creation from the latest observational data from baryon acoustic oscillations,cosmic chronometer,type Ia supernovae(Pantheon)including gamma-ray bursts,quasars and the local measurement of H_(0) from R21 data.Two different combinations of dataset provide a fairly tight constraint on the parameters of theΛCDM,VGCG and VCG models.The present values of various cosmological parameters are obtained,which are very close to theΛCDM model.Furthermore,we perform stability analysis,Bayesian evidence analysis and information criteria analysis for these models through studying the sound speed,Bayes factor,and Akaike information criteria(AIC)and Bayesian information criteria(BIC)selection criteria.The values of sound speed for VGCG and VCG models shows that both the models are stable.According to AIC,it is observed that VGCG and VCG models with matter creation are supported considerably less by current observations,while BIC shows that these models are not favoured by observational data.

Dynamical Evolution of Modified Chaplygin Gas

Based our previous work [Mod. Phys. Lett. A 22 （2007） 783, Gen. Relat. Gray. 39 （2007） 653], some properties of modified Chaplygin gas （MCG） as a dark energy model continue to be studied mainly in two aspects： one is the change rates of the energy density and energy transfer, and the other is the evolution of the growth index. It is pointed that the density of dark energy undergoes the change from decrease to increase no matter whether the interaction between dark energy and dark matter exists or not, but the corresponding transformation points are different from each other.Eurthermore, it is stressed that the MCG model even supports the existence of interaction between dark energy and dark matter, and the energy of transfer flows from dark energy to dark matter. The evolution of the interaction term with an ansatz 3Hc^2ρ is discussed with the MCG model. Moreover, the evolution of the growth index f in the MCG model without interaction is illustrated, from which we find that the evolutionary trajectory of f overlaps with that of the ACDM model when a 〉 0.7 and its theoretical value f ≈ 0.566 given by us at z = 0.15 is consistent with the observations.

The Hubble Constant Problem and the Solution by Gravitation in Flat Space-Time

General Relativity implies an expanding Universe from a singularity, the so-called Big Bang. The rate of expansion is the Hubble constant. There are two major ways of measuring the expansion of the Universe: through the cosmic distance ladder and through looking at the signals originated from the beginning of the Universe. These two methods give quite different results for the Hubble constant. Hence, the Universe doesn’t expand. The solution to this problem is the theory of gravitation in flat space-time where space isn’t expanding. All the results of gravitation for weak fields of this theory agree with those of General Relativity to measurable accuracy whereas at the beginning of the Universe the results of both theories are quite different, i.e. no singularity by gravitation in flat space-time and non-expanding universe, and a Big Bang (singularity) by General Relativity.

The interpretation of the CMBR

In the popular ACDM model,the cosmic microwave background radiation(CMBR)is thought to be the remnant of the early hot universe.An important precondition of this interpretation of CMBR is:after the last scattering surface formed,the high temperature ionized gases in the universe became low temperature neutral gases and so the universe has been completely transparent to the radiation which comes from the hot early universe.However,observations show that today most gases in the universe are still in a high temperature ionized state.The universe is not completely transparent to the radiation which comes from the hot early universe.According to the famous Sunyaev-Zeldovich effect,if the CMBR comes from the early hot universe and follows a perfect blackbody spectrum,the free electrons in the cosmic plasma will distort the perfect blackbody spectrum of the CMBR.In this case,the observed CMBR cannot be of a perfect blackbody spectrum.This is a fatal flaw in the interpretation of CMBR using the ACDM model.In order to overcome this fatal flaw,in this paper it is proposed that in the ACDM model frame,a better interpretation of CMBR is:The CMBR is a thermal equilibrium product between the high temperature ionized gases and the cosmic radiation field in the local universe space.