Universe In General Relativity Research Articles

The relic radiation blunder and the cosmometric contradiction in Big Bang cosmology

The cosmic microwave background radiation is routinely cited as evidence for a hot Big Bang. Its near isotropy harmonizes with the cosmological principle. However, in prototypical Big Bang models, all matter originates from a primeval fireball that also emits the light that is redshifted into these microwaves. Since light escapes from its source faster than matter can move, it would need to return for it to still be visible to material observers, but the universe is considered ‘flat’ and non-reflective. This prevents us from observing the redshifted glow of a primeval fireball. This is concealed by considering the light to expand with the ‘Hubble flow’ while disregarding that it would escape at _c_. This “relic radiation blunder” reflects the assumption that model universes in General Relativity are filled with a spatially homogeneous fluid. For radiation, this becomes inappropriate when it is no longer scattered. What we actually observe remains unexplained. Moreover, current standard cosmology allows an expanding view into a large pre-existing universe, while for some aspects it assumes the universe to have been smaller before. This creates geometric, i.e., “cosmometric” contradictions such as between the observed source of the cosmic microwaves and the much smaller and closer assumed emitting source of the same. The criticism expressed here goes against the ‘hard core’ of an established research program. Experts in the field normally view these cores as untouchable. This attitude blocks foundational advances in science.

The Big Bang theory: two fatal flaws

The cosmic microwave background radiation is routinely cited as evidence for a hot Big Bang. Its isotropy harmonizes with the cosmological principle. However, in prototypical Big Bang models, all matter originates from a primeval fireball that also emits the light that is redshifted into these microwaves. Since light escapes from its source faster than matter can move, it would need to return for it to still be visible to material observers, but the universe is considered ‘flat’ and non-reflective. This prevents us from observing the redshifted glow of the primeval fireball. Like its observability, its homogeneity would also be transient. This is concealed by considering the light to expand with the ‘Hubble flow’ while disregarding that it escapes at _c_. This blunder reflects the practice of treating model universes in General Relativity as filled with a spatially homogeneous fluid. For radiation, this becomes inappropriate when it is no longer scattered. What we actually observe remains unexplained. Moreover, the calculation of line-of-sight distances allows an expanding view into a large pre-existing universe. For other aspects, the universe is assumed to have been smaller before. This creates contradictions such as between the observed source of the cosmic microwaves and their much smaller and closer assumed emitting source. The criticism expressed here goes against the ‘hard core’ of an established research program. Those cores are treated as inviolable, which blocks fundamental progress. Such blockage can persist for generations even if the theory that is promulgated as the best we have is actually irrational.

CMB Power Spectrum in the Emergent Universe with K-Essence

The emergent universe provides a possible method to avoid the Big Bang singularity by considering that the universe stems from a stable Einstein static universe rather than the singularity. Since the Einstein static universe exists before inflation, it may leave some relics in the CMB power spectrum. In this paper, we analyze the stability condition for the Einstein static universe in general relativity with k-essence against both the scalar and tensor perturbations. Furthermore, we find the emergent universe can be successfully realized by constructing a scalar potential and an equation of state parameter. Solving the curved Mukhanov–Sasaki equation, we obtain the analytical approximation for the primordial power spectrum, and then depict the TT-spectrum of the emergent universe. The results show that both the primordial power spectrum and CMB TT-spectrum are suppressed on large scales.

BIANCHI TYPE V MAGNETIZED STRING DUST BULK VISCOUS FLUID COSMOLOGICAL MODELS WITH VARIABLE DECELERATION PARAMETER

We have investigated Bianchi type ∨ viscous fluid cosmological models with string dust universe in general relativity. Exact solution of Einstein eld equations have been obtained by choosing deceleration parameter is function of cosmic time. Solutions for exponential and polynomial form are obtained. Some geometrical and physical aspects of models are also discussed.

Cosmology in scalar-tensor f(R, T) gravity

In this work, we use reconstruction methods to obtain cosmological solutions in the recently developed scalar-tensor representation of $f(R,T)$ gravity. Assuming that matter is described by an isotropic perfect fluid and the spacetime is homogeneous and isotropic, i.e., the Friedmann-Lema\^{\i}tre-Robertson-Walker (FLRW) universe, the energy density, the pressure, and the scalar field associated with the arbitrary dependency of the action in $T$ can be written generally as functions of the scale factor. We then select three particular forms of the scale factor: an exponential expansion with $a(t)\ensuremath{\propto}{e}^{t}$ (motivated by the de Sitter solution); and two types of power-law expansion with $a(t)\ensuremath{\propto}{t}^{1/2}$ and $a(t)\ensuremath{\propto}{t}^{2/3}$ (motivated by the behaviors of radiation- and matter-dominated universes in general relativity, respectively). A complete analysis for different curvature parameters $k={\ensuremath{-}1,0,1}$ and equation of state parameters $w={\ensuremath{-}1,0,1/3}$ is provided. Finally, the explicit forms of the functions $f(R,T)$ associated with the scalar-field potentials of the representation used are deduced.

Helmoltz problem for the Riccati equation from an analogous Friedmann equation

We report a solution of the inverse Lagrangian problem for the first order Riccati differential equation by means of an analogy with the Friedmann equation of a suitable Friedmann–Lemaître–Robertson–Walker universe in general relativity. This analogous universe has fine-tuned parameters and is unphysical, but it suggests a Lagrangian and a Hamiltonian for the Riccati equation and for the many physical systems described by it.

Higher Dimensional Bianchi Type-I Cosmological Models With Massive String in General Relativity

Here we studied Bianchi type-I cosmological models with massive strings in general relativity in five dimensional space time. Out of the two different cases obtained here, one case leads to a five dimensional Bianchi type-I string cosmological model in general relativity while the other yields the vacuum Universe in general relativity in five dimensional space time. The physical and geometrical properties of the model Universe are studied and compared with the present day’s observational findings. It is observed that our model is anisotropic, expanding, shearing, and decelerates at an early stage and then accelerates at a later time. The model expands along x, y, and z axes and the extra dimension contracts and becomes unobservable at t → ∞. We also observed that the sum of the energy density (ρ) and the string tension density (λ) vanishes (ρ + λ = 0).

Interacting generalized anisotropic scalar field models

This paper is devoted to investigate the interacting generalized ghost pilgrim dark energy model in the background of anisotropic universe in general relativity. We analyze the two parameters i.e., hubble parameter and equation of state parameter to explore the cosmological evolution of the Bianchi type universe. We study scalar field dark energy models i.e., quintessence, dilaton, K-essence and tachyon to check the consistency of the current universe with their scalar field and corresponding potentials. Further, we check the compatibility of fractional density of matter and dark energy with recent observations of Plank along with their graphical analysis. It is remarkable to conclude that that both fractional densities admits consistency with Plank data 2018 in all cases of Bainchi type universe.

Bulk viscous LRS bianchi type-I cosmological model of the inflationary universe in general relativity

Bulk viscous LRS bianchi type-I cosmological model of the inflationary universe in general relativity

Energy–momentum distributions of Ruban universe in general relativity and teleparallel gravity

In this study, we obtain Einstein, Bergmann–Thomson (BT), Landau–Lifshitz (LL), Møller, Papapetrou (PP) and Tolman energy–momentum (EM) distributions for Ruban universe model in general relativity (GR) and teleparallel gravity (TG). We obtain same results for Einstein, Bergmann–Thomson and Landau–Lifshitz energy–momentum distributions in GR and TG. Also, we get same results for Einstein and Tolman energy–momentum distributions in GR. The Møller energy–momentum results are different in GR and TG. Also, using Ruban universe model, we obtain LRS Bianchi type I solutions and we get zero energy–momentum results for this universe model in GR and TG. These results of LRS Bianchi type I universe model agree with Aygün et al., Taşer et al., Doğru et al., Banerjee–Sen, Tryon and Xulu in different gravitation theories.

The shape of bouncing universes

What happens to the most general closed oscillating universes in general relativity? We sketch the development of interest in cyclic universes from the early work of Friedmann and Tolman to modern variations introduced by the presence of a cosmological constant. Then we show what happens in the cyclic evolution of the most general closed anisotropic universes provided by the Mixmaster universe. We show that in the presence of entropy increase its cycles grow in size and age, increasingly approaching flatness. But these cycles also grow increasingly anisotropic at their expansion maxima. If there is a positive cosmological constant, or dark energy, present then these oscillations always end and the last cycle evolves from an anisotropic inflexion point towards a de Sitter future of everlasting expansion.

Cyclic mixmaster universes

We investigate the behaviour of bouncing Bianchi type IX `Mixmaster' universes in general relativity. This generalises all previous studies of the cyclic behaviour of closed spatially homogeneous universes with and without entropy increase. We determine the behaviour of models containing radiation by analytic and numerical integration and show that increase of radiation entropy leads to increasing cycle size and duration. We introduce a null energy condition violating ghost field to create a smooth, non-singular bounce of finite size at the end of each cycle and compute the evolution through many cycles with and without entropy increase injected at the start of each cycle. In the presence of increasing entropy we find that the cycles grow larger and longer and the dynamics approach flatness, as in the isotropic case. However, successive cycles become increasingly anisotropic at the expansion maxima which is dominated by the general-relativistic effects of anisotropic 3-curvature. However, it becomes positive after expansion drives the dynamics close enough to isotropy for the curvature to become positive and for gravitational collapse to ensue. In the presence of a positive cosmological constant, radiation and a ghost field we show that, for a very wide range of cosmological constant values, the growing oscillations always cease and the dynamics subsequently approach those of the isotropic de Sitter universe at late times. This model is not included in the scope of earlier cosmic no-hair theorems because the 3-curvature can be positive. In the case of negative cosmological constant, radiation and an ultra-stiff field (to create non-singular bounces) we show that a sequence of chaotic oscillations also occurs, with sensitive dependence on initial conditions. In all cases, we follow the oscillatory evolution of the scale factors, the shear, and the 3-curvature from cycle to cycle.

Energy distributions of Bianchi type-VI h Universe in general relativity and teleparallel gravity

In this paper, we have investigated the energy and momentum density distributions for the inhomogeneous generalizations of homogeneous Bianchi type-VI h metric with Einstein, Bergmann–Thomson, Landau–Lifshitz, Papapetrou, Tolman and Moller prescriptions in general relativity (GR) and teleparallel gravity (TG). We have found exactly the same results for Einstein, Bergmann–Thomson and Landau–Lifshitz energy–momentum distributions in Bianchi type-VI h metric for different gravitation theories. The energy–momentum distributions of the Bianchi type- VI h metric are found to be zero for h = −1 in GR and TG. However, our results agree with Tripathy et al, Tryon, Rosen and Aygun et al.

Low redshift universe and a varying ghost dark energy

Recently, a phenomenological modification of ghost dark energy has been suggested and appropriate models of low redshift universe have been constructed. In this paper, we will consider a model of low redshift universe in General Relativity containing another model of varying ghost dark energy. In this model, an effective fluid is a radiation-like fluid in an early universe and evolves to quintessence dark energy in large scale universe. Cosmographic analysis of new model is performed and appropriate constraints on the parameters of the model are obtained. We have a look at suggested model via statefinder hierarchy in addition to thermodynamical description of it. We also study massless particle creation possibility in a radiation dominated universe of our cosmological model. According to our theoretical results, massless particle production is possible. To study particle creation, a straight analogy between quantization in Minkowski background and canonical quantization of a scalar field in curved dynamical backgrounds is taken into account.

Turnaround radius in modified gravity

In an accelerating universe in General Relativity there is a maximum radius above which a shell of test particles cannot collapse, but is dispersed by the cosmic expansion. This radius could be used in conjunction with observations of large structures to constrain the equation of state of the universe. We extend the concept of turnaround radius to modified theories of gravity for which the gravitational slip is non-vanishing.

Kasner Cosmological Models with Two-Fluid Source in General Relativity

In this paper we present Bianchi type-I metric of the Kasner form describing two-fluid source of the universe in general relativity. In Kasner cosmological models one fluid is a radiation field modeling the cosmic microwave background, while the other is a matter field, modeling material content of the universe. The radiation and matter content of the universe are in interactive phase. We have also presented anisotropic, homogeneous nature of Kasner cosmological models with two-fluid. The behavior of fluid parameters and kinematical parameters of the models are also discussed.

Exact de Sitter solutions in quadratic gravitation with torsion

Several exact cosmological solutions of quadratic gravitation with two torsion functions are presented. These solutions give an essentially different explanation from the one in most of previous works to the cause of the accelerating cosmological expansion and the origin of the torsion of the spacetime. These solutions can be divided into two classes. The solutions in the first class define the critical points of a dynamic system representing an asymptotically stable de Sitter spacetime. The solutions in the second class have exact analytic expressions which have never been found in the literature. The acceleration equation of the universe in general relativity is only a special case of them. These solutions indicate that even in vacuum the spacetime can be endowed with torsion, which means that the torsion of the spacetime has an intrinsic nature and a geometric origin. In these solutions the acceleration of the cosmological expansion is due to either the scalar torsion or the pseudoscalar torsion function. Neither a cosmological constant nor dark energy is needed. It is the torsion of the spacetime that causes the accelerating expansion of the universe in vacuum. All the effects of the inflation, the acceleration and the phase transformation from deceleration to acceleration can be explained by these solutions. Furthermore, the energy and pressure of the matter without spin can produce the torsion of the spacetime and make the expansion of the universe decelerate as well as accelerate.

Energy–momentum localization for Bianchi type-IV Universe in general relativity and teleparallel gravity

In this study we have investigated the energy–momentum distributions for homogeneous and anisotropic Bianchi type-IV in B class Universe. For this purpose, we have used energy–momentum complexes of Einstein, Bergmann–Thomson, Landau–Lifshitz (LL), Papapetrou, Tolman and Moller in general relativity (GR) is also Einstein, Bergmann–Thomson, Landau–Lifshitz and Moller in teleparallel gravity (TG). From the obtained results we have found that Einstein and Bergmann–Thomson distributions are exactly giving the same results in GR and TG but the Landau–Lifshitz, Papapetrou Tolman and Moller energy–momentum distributions do not provide the same results with Einstein and Bergmann–Thomson in GR and TG. Furthermore, Einstein, Bergmann–Thomson and LL results are the same in different gravitation theories and we get that both GR and TG are equivalent theories for these prescriptions. From the obtained solutions, we could say that these are equivalent theories. Also, Moller energy–momentum distributions do not give the same results in GR and TG. However, we have found that all energy prescriptions are negative and our results agree with Nester et al.

A higher-dimensional Bianchi type-I inflationary Universe in general relativity

A five-dimensional Bianchi type-I inflationary Universe is investigated in the presence of massless scalar field with a flat potential. To get an inflationary Universe, a flat region in which the potential V is constant is considered. Some physical and kinematical properties of the Universe are also discussed.

Axially Symmetric Bianchi Type-IX Inflationary Universe in General Relativity

Axially symmetric Bianchi type-IX space-time in the presence of mass less scalar field with a flat potential V is investigated. To get an inflationary universe, we have considered a flat region in which potential V is constant. Some physical and kinematical properties of the model are discussed.