Showing papers on "Big Rip published in 2007"
TL;DR: In this article, it is shown that modified gravity becomes complex at the region where the original phantom dark energy theory develops a Big Rip singularity, and that even for even scalar potentials, the ensuing modified gravity real.
291 citations
TL;DR: In this article, a string-motivated dark energy scenario featuring a scalar field coupled to the Gauss-Bonnet invariant is investigated, and the evolution of the universe in such a model, identifying its key properties.
262 citations
TL;DR: In this paper, the interplay between cosmological expansion and local attraction in a gravitationally bound system is revisited in various regimes, including weakly gravitating Newtonian systems, and various exact solutions describing a relativistic central object embedded in a Friedmann universe.
Abstract: The interplay between cosmological expansion and local attraction in a gravitationally bound system is revisited in various regimes. First, weakly gravitating Newtonian systems are considered, followed by various exact solutions describing a relativistic central object embedded in a Friedmann universe. It is shown that the ``all or nothing'' behavior recently discovered (i.e., weakly coupled systems are comoving while strongly coupled ones resist the cosmic expansion) is limited to the de Sitter background. New exact solutions are presented which describe black holes perfectly comoving with a generic Friedmann universe. The possibility of violating cosmic censorship for a black hole approaching the big rip is also discussed.
174 citations
TL;DR: A cyclic model is described, in which dark energy with w<-1 equation of state leads to a turnaround at a time, extremely shortly before the would-be big rip, at which both volume and entropy of the authors' Universe decrease by a gigantic factor, while very many independent similarly small contracting universes are spawned.
Abstract: It is speculated how dark energy in a brane world can help reconcile an infinitely cyclic cosmology with the second law of thermodynamics. A cyclic model is described, in which dark energy with w<-1 equation of state leads to a turnaround at a time, extremely shortly before the would-be big rip, at which both volume and entropy of our Universe decrease by a gigantic factor, while very many independent similarly small contracting universes are spawned. The entropy of our model decreases almost to zero at turnaround but increases for the remainder of the cycle by a vanishingly small amount during contraction, empty of matter, then by a large factor during inflationary expansion.
165 citations
TL;DR: In this article, the existence of the dark energy in the present universe could be linked to the quantum field theoretical mechanism that may have triggered primordial inflation in the early Universe, which induces a logarithmic, asymptotically-free, running of the gravitational coupling.
Abstract: The discovery of dark energy (DE) as the physical cause for the accelerated expansion of the Universe is the most remarkable experimental finding of modern cosmology. However, it leads to insurmountable theoretical difficulties from the point of view of fundamental physics. Inflation, on the other hand, constitutes another crucial ingredient, which seems necessary to solve other cosmological conundrums and provides the primeval quantum seeds for structure formation. One may wonder if there is any deep relationship between these two paradigms. In this work, we suggest that the existence of the DE in the present Universe could be linked to the quantum field theoretical mechanism that may have triggered primordial inflation in the early Universe. This mechanism, based on quantum conformal symmetry, induces a logarithmic, asymptotically-free, running of the gravitational coupling. If this evolution persists in the present Universe, and if matter is conserved, the general covariance of Einstein's equations demands the existence of dynamical DE in the form of a running cosmological term whose variation follows a power law of the redshift.
137 citations
TL;DR: In this article, the cosmological evolution of the holographic dark energy in a cyclic universe was studied and a link condition was proposed to give rise to a complete picture of holographic evolution in the cyclic model.
Abstract: In this paper we study the cosmological evolution of the holographic dark energy in a cyclic universe, generalizing the model of holographic dark energy proposed by Li. The holographic dark energy with c < 1 can realize a quintom behavior; namely, it evolves from a quintessence-like component to a phantom-like one. The holographic phantom energy density grows rapidly and dominates the late-time expanding phase, helping to realize a cyclic universe scenario in which the high energy regime is modified by the effects of quantum gravity, causing a turn-around (and a bounce) of the universe. The dynamical evolution of holographic dark energy in the regimes of low energy and high energy is governed by two differential equations, respectively. It is of importance to link the two regimes for this scenario. We propose a link condition giving rise to a complete picture of holographic evolution of a cyclic universe.
134 citations
TL;DR: In this paper, a unified description of the early evolution of universe is presented with a number of possible assumptions on the bulk viscous term and cosmological constant in which an inflationary phase is followed by radiation-dominated phase.
Abstract: Einstein's field equations with variable gravitational and cosmological 'constants' are considered in the presence of bulk viscosity for a spatially flat homogeneous and isotropic universe. Solutions are obtained by using a 'gamma-law' equation of state p = (? ? 1)?, where the adiabatic parameter ? varies continuously as the universe expands. A unified description of the early evolution of universe is presented with a number of possible assumptions on the bulk viscous term and gravitational constant in which an inflationary phase is followed by radiation-dominated phase. We investigate the cosmological model with constant and time-dependent bulk viscosity (proportional to power function of energy density and to Hubble parameter) along with constant and variable gravitational constant. The effect of viscosity is shown to affect the past and future of the universe. In all cases, the cosmological constant ? is found to be positive and a decreasing function of time, which supports the results obtained from recent supernovae Ia observations. The possibility that the present acceleration of the universe is driven by a kind of viscous fluid is explained. At the background level this model is similar to the generalized Chaplygin gas model. The physical and geometrical significance of the early cosmological models has also been discussed.
102 citations
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TL;DR: In this article, the authors compare two forms of the Robertson-Walker (RW) metric, written in (the traditional) comoving coordinates, and a set of observer-dependent coordinates, first for the well known de Sitter universe containing only dark energy, and then for a newly derived form of the RW metric, for a universe with dark energy and matter.
Abstract: The cosmological principle, promoting the view that the universe is homogeneous and isotropic, is embodied within the mathematical structure of the Robertson-Walker (RW) metric. The equations derived from an application of this metric to the Einstein Field Equations describe the expansion of the universe in terms of comoving coordinates, from which physical distances may be derived using a time-dependent expansion factor. These coordinates, however, do not explicitly reveal properties of the cosmic spacetime manifested in Birkhoff's theorem and its corollary. In this paper, we compare two forms of the metric--written in (the traditional) comoving coordinates, and a set of observer-dependent coordinates--first for the well-known de Sitter universe containing only dark energy, and then for a newly derived form of the RW metric, for a universe with dark energy and matter. We show that Rindler's event horizon--evident in the co-moving system--coincides with what one might call the "curvature horizon" appearing in the observer-dependent frame. The advantage of this dual prescription of the cosmic spacetime is that with the latest WMAP results, we now have a much better determination of the universe's mass-energy content, which permits us to calculate this curvature with unprecedented accuracy. We use it here to demonstrate that our observations have probed the limit beyond which the cosmic curvature prevents any signal from having ever reached us. In the case of de Sitter, where the mass-energy density is a constant, this limit is fixed for all time. For a universe with a changing density, this horizon expands until de Sitter is reached asymptotically, and then it too ceases to change.
99 citations
TL;DR: In this article, the authors investigated the thermodynamic properties of the universe with dark energy and showed that the apparent horizon is the physical horizon in dealing with thermodynamics problems, based on the well known correspondence between the Friedmann equation and the first law of thermodynamics of the visible horizon.
Abstract: We have investigated the thermodynamical properties of the Universe with dark energy Adopting the usual assumption in deriving the constant co-moving entropy density that the physical volume and the temperature are independent, we observed some strange thermodynamical behaviours However, these strange behaviours disappeared if we considered the realistic situation where the physical volume and the temperature of the Universe are related On the basis of the well known correspondence between the Friedmann equation and the first law of thermodynamics of the apparent horizon, we argued that the apparent horizon is the physical horizon in dealing with thermodynamics problems We have concentrated on the volume of the Universe within the apparent horizon and considered that the Universe is in thermal equilibrium with the Hawking temperature on the apparent horizon For dark energy with w ≥ −1, the holographic principle and the generalized second law are always respected
99 citations
TL;DR: In this paper, a dynamical system of phantom scalar field under exponential potential in the background of loop quantum cosmology was considered, and it was shown that the universe always bounces after accelerating even in the domination of the phantom field.
Abstract: We consider a dynamical system of phantom scalar field under exponential potential in the background of loop quantum cosmology. In our analysis, there is neither stable node nor repeller unstable node but only two saddle points, hence no big rip singularity. Physical solutions always possess potential energy greater than the magnitude of the negative kinetic energy. We found that the universe bounces after accelerating even in the domination of the phantom field. After bouncing, the universe finally enters the oscillatory regime.
84 citations
TL;DR: In this paper, the authors consider a varying equation of state parameter dependent on the radial coordinate, i.e., ω(r) = p(r)/ρ(r).
Abstract: A possible candidate for the late time accelerated expanding universe is phantom energy, which possesses rather bizarre properties, such as the prediction of a Big Rip singularity and the violation of the null energy condition. The latter is a fundamental ingredient of traversable wormholes, and it has been shown that phantom energy may indeed sustain these exotic geometries. Inspired by the evolving dark energy parameter crossing the phantom divide, we consider in this work a varying equation of state parameter dependent on the radial coordinate, i.e., ω(r) = p(r)/ρ(r). We shall impose that phantom energy is concentrated in the neighbourhood of the throat, to ensure the flaring out condition, and several models are analysed. We shall also consider the possibility that these phantom wormholes be sustained by their own quantum fluctuations. The energy density of the graviton one-loop contribution to a classical energy in a phantom wormhole background and the finite one-loop energy density are considered as a self-consistent source for these wormhole geometries. The latter semi-classical approach prohibits solutions with a constant equation of state parameter, which further motivates the imposition of a radial dependent parameter, ω(r), and only permits solutions with a steep positive slope proportional to the radial derivative of the equation of state parameter, evaluated at the throat. The size of the wormhole throat as a function of the relevant parameters is also explored.
TL;DR: In this paper, the universe content is considered as a non-perfect fluid with bulk viscosity and is described by a more general equation of state (endowed some deviation from the conventionally assumed cosmic perfect fluid model).
Abstract: The universe content is considered as a non-perfect fluid with bulk viscosity and is described by a more general equation of state (endowed some deviation from the conventionally assumed cosmic perfect fluid model). We assume the bulk viscosity is a linear combination of two terms: one is constant, and the other is proportional to the scalar expansion θ = 3/a. The equation of state is described as p = (γ−1)ρ+p0, where p0 is a parameter. In this framework we demonstrate that this model can be used to explain the dark energy dominated universe, and different proper choices of the parameters may lead to three kinds of fates of the cosmological evolution: no future singularity, big rip, or Type-III singularity as presented in [S. Nojiri, S.D. Odintsov, and S. Tsujikawa, Phys. Rev. D 71 (2005) 063004].
TL;DR: In this paper, it was shown that singularities may not be originated from the phantom nature of the fluid, and that if initially the tension of the brane in a brane-world Chaplygin model is large enough then an infrared cut off appears in the past.
Abstract: Although it has been believed that the models with generalised Chaplygin gas do not contain singularities, in a previous work we have studied how a big freeze could take place in some kinds of phantom generalised Chaplygin gas. In the present work, we study some types of generalised Chaplygin gas in order to show how different sorts of singularities could appears in such models, in the future or in the past. We point out that: (i) singularities may not be originated from the phantom nature of the fluid, and (ii) if initially the tension of the brane in a brane-world Chaplygin model is large enough then an infrared cut off appears in the past.
TL;DR: In this article, the authors discuss the constraints coming from current observations of type Ia supernovae on cosmological models which allow sudden future singularities of pressure (with the scale factor and the energy density regular).
Abstract: We discuss the constraints coming from current observations of type Ia supernovae on cosmological models which allow sudden future singularities of pressure (with the scale factor and the energy density regular). We show that such a sudden singularity may happen in the very near future (e.g. within $10\ifmmode\times\else\texttimes\fi{}{10}^{6}\text{ }\text{ }\mathrm{\text{years}}$) and its prediction at the present moment of cosmic evolution cannot be distinguished, with current observational data, from the prediction given by the standard quintessence scenario of future evolution. Fortunately, sudden future singularities are characterized by a momentary peak of infinite tidal forces only; there is no geodesic incompleteness, which means that the evolution of the universe may eventually be continued throughout until another ``more serious'' singularity such as a big crunch or big rip.
TL;DR: In this paper, the future event horizon is chosen as the horizon of the flat Friedmann-Lemaitre-Robertson-Walker universe, and the interacting holographic dark energy model is able to explain the phantom divide line crossing.
Abstract: Choosing the future event horizon as the horizon of the flat Friedmann–Lemaitre–Robertson–Walker universe, we show that the interacting holographic dark energy model is able to explain the phantom divide line crossing. We show that if we take the particle event horizon as the horizon of the universe, besides describing the ω = −1 crossing (based on astrophysical data), we are able to determine appropriately the ratio of dark matter to dark energy density at the transition time. In this approach, after the first transition from the quintessence to the phantom phase, there is another transition from the phantom to the quintessence phase which avoids the big rip singularity.
TL;DR: In this paper, it was shown that the cosmological deceleration of the solar system can be approximated by a factor of 10 orders of magnitude with respect to estimates from observational cosmology.
Abstract: The gravitational action of the smooth energy-matter components filling in the universe can affect the orbit of a planetary system. Changes are related to the acceleration of the cosmological scale size R. In a universe with significant dark matter, a gravitational system expands or contracts according to the amount and equation of state of the dark energy. At present time, the Solar System, according to the {lambda}CDM scenario emerging from observational cosmology, should be expanding if we consider only the effect of the cosmological background. Its fate is determined by the equation of state of the dark energy alone. The mean motion and periastron precession of a planet are directly sensitive to Re/R, whereas variations with time in the semimajor axis and eccentricity are related to its time variation. Actual bounds on the cosmological deceleration parameters q{sub 0} from accurate astrometric data of perihelion precession and changes in the third Kepler's law in the Solar System fall short of 10 orders of magnitude with respect to estimates from observational cosmology. Future radio-ranging measurements of outer planets could improve actual bounds by 5 orders of magnitude.
TL;DR: In this article, it was shown that if the universe is only filled with generalized phantom Chaplygin gas with equation of state $p=-c^2s^2/\rho^{\alpha}$ with $\alpha<-1$, then such a model cannot be matched to the data of astronomical observations.
Abstract: Recently it was found that dark energy in the form of phantom generalized Chaplygin gas may lead to a new form of the cosmic doomsday, the big freeze singularity. Like the big rip singularity, the big freeze singularity would also take place at a finite future cosmic time, but unlike the big rip singularity it happens for a finite scale factor.Our goal is to test if a universe filled with phantom generalized Chaplygin gas can conform to the data of astronomical observations. We shall see that if the universe is only filled with generalized phantom Chaplygin gas with equation of state $p=-c^2s^2/\rho^{\alpha}$ with $\alpha<-1$, then such a model cannot be matched to the data of astronomical observations. To construct matched models one actually need to add dark matter. This procedure results in cosmological scenarios which do not contradict the data of astronomical observations and allows one to estimate how long we are now from the future big freeze doomsday.
TL;DR: In this paper, the authors investigate observational constraints on the curvature of the universe not restricting ourselves to a cosmological constant as dark energy, in particular allowing a dark energy equation of state to evolve with time in several ways.
Abstract: We investigate observational constraints on the curvature of the universe not restricting ourselves to a cosmological constant as dark energy, in particular allowing a dark energy equation of state to evolve with time in several ways. We use type Ia supernovae (SNeIa) data from the latest gold data set which includes 182 SNeIa, along with the cosmic microwave background shift parameter and the baryon acoustic oscillation peak. We show quantitatively that the constraint on the curvature of the universe depends on the dark energy model: some popular parametrizations give constraints closely around the flat universe at 5% level (2σ C.L.) whereas some parametrizations allow the universe to be as open as having Ωk ~ 0.2.
TL;DR: In this article, the authors investigate the effect of the bulk content in the general Gauss-Bonnet braneworld on the evolution of the universe and find that the combination of the dark radiation and the matter content plays a crucial role in the universe's evolution.
Abstract: We investigate the effect of the bulk content in the general Gauss-Bonnet braneworld on the evolution of the Universe. We find that the Gauss-Bonnet term and the combination of the dark radiation and the matter content of the bulk play a crucial role in the Universe's evolution. We show that our model can describe the superacceleration of our Universe with the equation of state of the effective dark energy in agreement with observations.
TL;DR: In this paper, a modified Chaplygin gas (MCG) model of unifying dark energy and dark matter is considered, in which dark energy interacts with dark matter, and the evolution of such a unified dark sectors model is studied and the statefinder diagnostic to the MCG model is performed in our model.
Abstract: A modified Chaplygin gas (MCG) model of unifying dark energy and dark matter is considered in this paper, in which dark energy interacts with dark matter. Concretely, the evolution of such a unified dark sectors model is studied and the statefinder diagnostic to the MCG model is performed in our model. By analysis, it is shown that the effective equation of state (EoS) parameter of dark energy can cross the so-called phantom divide ω = −1, the behavior of MCG will be like ΛCDM in the future and therefore our Universe will not end up with Big Rip in the future. Furthermore, we plot the evolution trajectories of the MCG model in the statefinder parameter r–s plane and illustrate the discrimination between this scenario and the generalized Chaplygin gas (GCG) model.
TL;DR: In this article, the future event horizon is chosen as the horizon of the flat FLRW universe to explain the phantom divide line crossing, but the thermodynamics second law is not respected in this model.
Abstract: By choosing the future event horizon as the horizon of the flat FLRW universe, we show that although the interacting holographic dark energy model is able to explain the phantom divide line crossing, but the thermodynamics second law is not respected in this model. We show that if one takes the particle event horizon as the horizon of the universe, besides describing $\omega=-1$ crossing in a consistent way with thermodynamics second law, he is able to determine appropriately the ratio of dark matter to dark energy density at transition time. In this approach, after the first transition from quintessence to phantom, there is another transition from phantom to quintessence phase which avoids the big rip singularity.
TL;DR: In this article, the authors discuss FRW universe with time-dependent EoS dark fluid which leads to multiple de Sitter space and the possibility of transitions between universe regions with positive and negative cosmological constant is also established.
TL;DR: In this paper, it was shown that as we extrapolate the current CDM universe forward in time, all evidence of the Hubble expansion will disappear, so that observers in our "island universe" will be fundamentally incapable of determining the true nature of the universe.
Abstract: We demonstrate that as we extrapolate the current $\Lambda$CDM universe forward in time, all evidence of the Hubble expansion will disappear, so that observers in our "island universe" will be fundamentally incapable of determining the true nature of the universe, including the existence of the highly dominant vacuum energy, the existence of the CMB, and the primordial origin of light elements. With these pillars of the modern Big Bang gone, this epoch will mark the end of cosmology and the return of a static universe. In this sense, the coordinate system appropriate for future observers will perhaps fittingly resemble the static coordinate system in which the de Sitter universe was first presented.
TL;DR: In this paper, the Euler and Gibbs relations permit two different possibilities for the entropy and temperature: a situation in which the entropy is negative and the temperature is positive or vice versa.
Abstract: The accretion of phantom fields by black holes within a thermodynamic context is addressed. For a fluid violating the dominant energy condition, the case of a phantom fluid, the Euler and Gibbs relations permit two different possibilities for the entropy and temperature: a situation in which the entropy is negative and the temperature is positive or vice versa. In the former case, if the generalized second law (GSL) is valid, then the accretion process is not allowed whereas in the latter, there is a critical black hole mass below which the accretion process occurs. In a universe dominated by a phantom field, the critical mass drops quite rapidly with the cosmic expansion and black holes are only slightly affected by accretion. All black holes disappear near the big rip, as suggested by previous investigations, if the GSL is violated.
TL;DR: In this article, the authors discuss astronomical and astrophysical evidence, which relate to the principle of zero-total energy of the universe, that imply several relations among the mass M, the radius R and the angular momentum L of a sphere representing a Machian universe.
Abstract: We discuss astronomical and astrophysical evidence, which we relate to the principle of zero-total energy of the Universe, that imply several relations among the mass M, the radius R and the angular momentum L of a “large” sphere representing a Machian Universe. By calculating the angular speed, we find a peculiar centripetal acceleration for the Universe. This is an ubiquituous property that relates one observer to any observable. It turns out that this is exactly the anomalous acceleration observed on the Pioneers spaceships. We have thus shown that this anomaly is to be considered a property of the Machian Universe. We discuss several possible arguments against our proposal.
TL;DR: By analysis, it is shown that the state parameter of dark energy can cross the so-called phantom divide ω = -1, the behavior of MCG will be like ΛCDM in the future and therefore the universe will not end up with Big Rip in thefuture.
Abstract: A modified Chaplygin gas (MCG) model of unifying dark energy and dark matter is considered in this paper. Concretely, the evolution of such a unified dark sector model is studied and the statefinder diagnostic to the MCG model is performed in our model. By analysis, it is shown that the state parameter of dark energy can cross the so-called phantom divide ω = -1, the behavior of MCG will be like ΛCDM in the future and therefore our universe will not end up with Big Rip in the future. In addition, we plot the evolution trajectory of the MCG model in the statefinder parameter r–s plane and show the discrimination between this scenario and other dark energy models.
TL;DR: The origin of the Big Bang hypothesis has been examined in detail in detail by as discussed by the authors, who investigated how the Belgian physicist and cosmologist Georges Lemaitre in 1931 arrived at the hypothesis that the universe had begun in a Big Bang, or what he called a primeval atom.
Abstract: Summary In spite of the paradigmatic status of the Big Bang model of the universe, the genesis of this idea has never been examined in detail. This paper investigates how the Belgian physicist and cosmologist Georges Lemaitre in 1931 arrived at the hypothesis that the universe had begun in a Big Bang, or what he called a ‘primeval atom’. Four years earlier, he had suggested a closed expanding model in which the universe slowly inflated from an equilibrium Einstein state, but in 1931 he advocated an abrupt beginning from an initial, superdense concentration of nuclear matter. Why did Lemaitre believe that the universe had a definite beginning a finite time ago? It turns out that the law of increase of entropy was one motivation, and that the existence of long-lived radioactive substances was another. Contrary to what is often stated, he most likely had the idea of an exploding universe before 1931. Among his chief inspirations to think about the origin of the universe, we draw attention to his persistent f...
TL;DR: In this article, it was shown that dark energy emerges from higher-derivative gravity with a non-linear term proportional to R 2 and R 3 with R being the Ricci scalar curvature.
TL;DR: In this paper, the Euler and Gibbs relations permit two different possibilities for the entropy and temperature: a situation in which the entropy is negative and the temperature is positive or vice-versa.
Abstract: The accretion of phantom fields by black holes within a thermodynamic context is addressed. For a fluid violating the dominant energy condition, case of a phantom fluid, the Euler and Gibbs relations permit two different possibilities for the entropy and temperature: a situation in which the entropy is negative and the temperature is positive or vice-versa. In the former case, if the generalized second law (GSL) is valid, then the accretion process is not allowed whereas in the latter, there is a critical black hole mass below which the accretion process occurs. In a universe dominated by a phantom field, the critical mass drops quite rapidly with the cosmic expansion and black holes are only slightly affected by accretion. All black holes disappear near the big rip, as suggested by previous investigations, if the GSL is violated.
TL;DR: For the Poincare gauge theory of gravity, the authors explored the possibility of using dynamical scalar torsion to explain the current state of the accelerating universe and showed that with certain suitable sets of chosen parameters, this model can give a (qualitatively) proper description of the current universe without a cosmological constant.
Abstract: For the Poincare gauge theory of gravity we consider the dynamical scalar torsion mode in a cosmological context. We explore in particular the possibility of using dynamical torsion to explain the current state of the accelerating Universe. With certain suitable sets of chosen parameters, this model can give a (qualitatively) proper description of the current universe without a cosmological constant, and the universe described is oscillating with a period of the Hubble time.