Showing papers on "Particle horizon published in 2002"
TL;DR: In this article, a cyclic model of the universe is proposed based on concepts drawn from the ekpyrotic scenario and M theory, and the universe undergoes an endless sequence of cosmic epochs.
Abstract: Based on concepts drawn from the ekpyrotic scenario and M theory, we elaborate our recent proposal of a cyclic model of the universe. In this model, the universe undergoes an endless sequence of cosmic epochs which begin with the universe expanding from a ``big bang'' and end with the universe contracting to a ``big crunch.'' Matching from ``big crunch'' to ``big bang'' is performed according to the prescription recently proposed with Khoury, Ovrut and Seiberg. The expansion part of the cycle includes a period of radiation and matter domination followed by an extended period of cosmic acceleration at low energies. The cosmic acceleration is crucial in establishing the flat and vacuous initial conditions required for ekpyrosis and for removing the entropy, black holes, and other debris produced in the preceding cycle. By restoring the universe to the same vacuum state before each big crunch, the acceleration ensures that the cycle can repeat and that the cyclic solution is an attractor.
783 citations
TL;DR: A cosmological model in which the universe undergoes an endless sequence of cosmic epochs that begin with a "bang" and end in a “crunch" is proposed, which produces the homogeneity, flatness, and energy needed to begin the next cycle.
Abstract: We propose a cosmological model in which the universe undergoes an endless sequence of cosmic epochs that begin with a “bang” and end in a “crunch.” Temperature and density at the transition remain finite. Instead of having an inflationary epoch, each cycle includes a period of slow accelerated expansion (as recently observed) followed by contraction that produces the homogeneity, flatness, and energy needed to begin the next cycle.
609 citations
TL;DR: In this article, a modification to the Friedmann-Robertson-Walker equation is proposed in which the universe is flat, matter dominated, and accelerating, and an additional term which contains only matter or radiation (no vacuum contribution) becomes the dominant driver of expansion at a late epoch of the universe.
464 citations
TL;DR: In the model where the universe is considered as a thin shell expanding in five-dimensional hyper-space, there is a possibility to obtain one scale for particle theory corresponding to the fivedimensional cosmological constant and Universe thickness as mentioned in this paper.
Abstract: In the model where the Universe is considered as a thin shell expanding in five-dimensional hyper-space there is a possibility to obtain one scale for particle theory corresponding to the five-dimensional cosmological constant and Universe thickness.
231 citations
TL;DR: The Cardassian universe as discussed by the authors is a proposed modification to the Friedmann Robertson Walker (FRW) equation in which the universe is flat, matter dominated, and accelerating, and it is shown that the Cardassian model survives several observational tests, including the cosmic background radiation, the age of the universe, the cluster baryon fraction, and structure formation.
Abstract: The Cardassian universe is a proposed modification to the Friedmann Robertson Walker (FRW) equation in which the universe is flat, matter dominated, and accelerating. Here we generalize the original Cardassian proposal to include additional variants on the FRW equation. Specific examples are presented.
In the ordinary FRW equation, the right hand side is a linear function of the energy density, $H^2 \sim \rho$. Here, instead, the right hand side of the FRW equation is a different function of the energy density, $H^2 \sim g(\rho)$. This function returns to ordinary FRW at early times, but modifies the expansion at a late epoch of the universe. The only ingredients in this universe are matter and radiation: in particular, there is {\it no} vacuum contribution. Currently the modification of the FRW equation is such that the universe accelerates. The universe can be flat and yet consist of only matter and radiation, and still be compatible with observations. The energy density required to close the universe is much smaller than in a standard cosmology, so that matter can be sufficient to provide a flat geometry. The modifications may arise, e.g., as a consequence of our observable universe living as a 3-dimensional brane in a higher dimensional universe. The Cardassian model survives several observational tests, including the cosmic background radiation, the age of the universe, the cluster baryon fraction, and structure formation. As will be shown in future work, the predictions for observational tests of the generalized Cardassian models can be very different from generic quintessence models, whether the equation of state is constant or time dependent.
58 citations
TL;DR: In this paper, the magnitude-redshift relation for Type Ia supernovae was reinterpreted to explain the current observations of the universe, which explains the current acceleration in the universe.
Abstract: It is generally argued that present cosmological observations support the accelerating models of the universe, as driven by a cosmological constant or "dark energy." We argue here that an alternative model of the universe is possible, which explains the current observations of the universe. We demonstrate this with a reinterpretation of the magnitude-redshift relation for Type Ia supernovae, since this was the test that gave a spurt to the current trend in favor of the cosmological constant.
55 citations
TL;DR: A cosmological model based on Kaluza-Klein theory is studied in this paper, in which the scale factor of the compact space evolves as an inverse power of the radius of the observable universe, and the Freedmann-Robertson-Walker equations of standard four-dimensional cosmology are obtained precisely.
Abstract: A cosmological model based on Kaluza-Klein theory is studied. A metric, in which the scale factor of the compact space evolves as an inverse power of the radius of the observable universe, is constructed. The Freedmann-Robertson-Walker equations of standard four-dimensional cosmology are obtained precisely. The pressure in our universe is an effective pressure expressed in terms of the components of the higher dimensional energy-momentum tensor. In particular, this effective pressure could be negative and might therefore explain the acceleration of our present universe. A special feature of this model is that, for a suitable choice of the parameters of the metric, the higher dimensional gravitational coupling constant could be negative.
55 citations
TL;DR: In this article, the authors present a new numerical treatment of the evolution of primordial magnetic fields and apply it to weakly helical seeds as they occur in certain early Universe scenarios, finding that initial helicities not much larger than the baryon to photon number can lead to fields of about 10 − 13 Gauss with coherence scales slightly below a kilo-parsec today.
Abstract: Most early Universe scenarios predict negligible magnetic fields on cosmological scales if they are unprocessed during subsequent expansion of the Universe. We present a new numerical treatment of the evolution of primordial fields and apply it to weakly helical seeds as they occur in certain early Universe scenarios. We find that initial helicities not much larger than the baryon to photon number can lead to fields of about 10^{-13} Gauss with coherence scales slightly below a kilo-parsec today.
53 citations
TL;DR: In this article, the mass power spectrum for a universe dominated by the Chaplygin gas is evaluated numerically from scales of the order of the Hubble horizon to 100 Mpc, and the results are compared with a pure baryonic model and a cosmological constant model.
Abstract: The mass power spectrum for a Universe dominated by the Chaplygin gas is evaluated numerically from scales of the order of the Hubble horizon to 100 Mpc. The results are compared with a pure baryonic Universe and a cosmological constant model. In all three cases, the spectrum increases with k, the wavenumber of the perturbations. The slope of the spectrum is higher for the baryonic model and smaller for the cosmological constant model, the Chaplygin gas interpolating these two models. The results are analyzed in terms of the sound velocity of the Chaplygin gas and the moment the Universe begins to accelerate.
51 citations
TL;DR: In this paper, it was shown that the universe started in an unstable de Sitter state, by semiclassical tunneling via a Hawking-Moss instanton, and that an expanding universe is most likely to emerge from this state by using the no boundary proposal to specify the class of histories.
Abstract: We show why the universe started in an unstable de Sitter state. The quantum origin of our universe implies one must take a ``top down'' approach to the problem of initial conditions in cosmology, in which the histories that contribute to the path integral depend on the observable being measured. Using the no boundary proposal to specify the class of histories, we study the quantum cosmological origin of an inflationary universe in theories such as trace anomaly driven inflation in which the effective potential has a local maximum. We find that an expanding universe is most likely to emerge in an unstable de Sitter state, by semiclassical tunneling via a Hawking-Moss instanton. Since the top down view is forced upon us by the quantum nature of the universe, we argue that the approach developed here should still apply when the framework of quantum cosmology will be based on M theory.
48 citations
TL;DR: In this paper, the Friedmann-Lemaitre model was proposed as the standard model of the universe and a new formula for the point of time when decelerated expansion changed into accelerated expansion was given.
Abstract: Up to about four years ago the dynamical properties of the evolution of the universe were assumed to be well described by the Einstein-de Sitter universe model, which is a flat universe model dominated by cold matter. However, the discovery that the cosmic expansion is accelerating made it clear that, at the present time, the evolution of the universe is dominated by some sort of vacuum energy with repulsive gravitation. The most simple type of vacuum energy is the Lorentz invariant vacuum energy which has constant energy density during the expansion of the universe. This type of vacuum may be represented mathematically by including a cosmological constant in Einstein's field equations. Hence, the flat Friedmann-Lemaitre model, which is a universe model with cold matter and vacuum energy, has replaced the Einstein-de Sitter model as the standard model of the universe. In this paper we give a pedagogical presentation of this model, including, among others, a new formula for the point of time when decelerated expansion changed into accelerated expansion.
TL;DR: In this article, the authors present arguments against the inflationary cosmologies, arguing that both of them are essentially identical from the viewpoint of their application to the observable universe and that they cannot be applied to the real world.
Abstract: This paper reviews two cosmologies which assume that the observable universe was initially vacuumlike (i.e., the cosmological medium was Lorentz invariant). In the earlier nonsingular Friedmann cosmology, the Friedmann universe comes into being during the phase transition of an initial vacuumlike state to the state of 'ordinary' matter. In the course of this transition, the emerging matter is accelerated, which causes the universe to expand and attain the Friedmann expansion regime. In the inflationary cosmology, the transition to the Friedmann universe is preceded by an epoch of inflation in which the universe grows spontaneously by many tens of orders of magnitude without or almost without changes in its composition and density. The idea of inflation gives rise to a variety of scenarios involving a cosmological singularity, or the birth of one universe within another, or the world-as-a-whole as an infinite set of universes, etc. The present paper provides arguments against the inflation idea. On dismissing it, both cosmologies are essentially identical from the viewpoint of their application to the observable universe.
TL;DR: In this article, the evolution of the observable part of the universe has been studied from a cosmological point of view, and a new concept, the Q-sphere (or Q-space, in the case of quintessence) is introduced.
Abstract: We consider ever-expanding big bang models with a cosmological constant, Λ, and investigate in detail the evolution of the observable part of the universe. We also discuss quintessence models from the same point of view. A new concept, the Λ-sphere (or Q-sphere, in the case of quintessence) is introduced. This is the surface in our visible universe that bounds the region where dark energy dominates the expansion, and within which the universe is accelerating. We follow the evolution of this surface as the universe expands, and we also investigate the evolution of the particle and event horizons as well as the Hubble surface. We calculate the extent of the observable universe and the portion of it that can be seen at different epochs. Furthermore, we trace the changes in redshift, apparent magnitude and apparent size of distant sources through cosmic history. Our approach is different from, but complementary to, most other contemporary investigations, which concentrate on the past light cone at the present epoch. When presenting numerical results we use the FRW world model with Ωm0 = 0.30 and ΩΛ0 = 0.70 as our standard cosmological model. In this model the Λ-sphere is at a redshift of 0.67, and within a few Hubble times the event horizon will be stationary at a fixed proper distance of 5.1 Gpc (assuming h0 = 0.7). All cosmological sources with present redshift larger than 1.7 have by now crossed the event horizon and are therefore completely out of causal contact.
TL;DR: In this paper, the existence of shear-free cosmological models with rotation and expansion which support inflationary scenarios was demonstrated and the corresponding metrics belong to the family of spatially homogeneous models with the geometry of the closed universe.
Abstract: We demonstrate the existence of shear-free cosmological models with rotation and expansion which support inflationary scenarios. The corresponding metrics belong to the family of spatially homogeneous models with the geometry of the closed universe (Bianchi type IX). We show that the global vorticity does not prevent inflation and can even accelerate it.
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31 Jan 2002TL;DR: In this paper, the authors used the universe's spots to observe global geometry in a manner analogous to the use of multiple images of a gravitationally lensed quasar to study the geometry of the lens.
Abstract: The universe displays a three-dimensional pattern of hot and cold spots in the radiation remnant from the big bang. The global geometry of the universe can be revealed in the spatial distribution of these spots. In a topologically compact universe, distinctive patterns are especially prominent in spatial correlations of the radiation temperature. Whereas these patterns are usually washed out in statistical averages, we propose a scheme which uses the universe’s spots to observe global geometry in a manner analogous to the use of multiple images of a gravitationally lensed quasar to study the geometry of the lens. To demonstrate how the geometry of space forms patterns, we develop a simple real-space approximation to estimate temperature correlations for any set of cosmological parameters and any global geometry. We present correlated spheres which clearly show topological pattern formation for compact flat universes as well as for the compact negatively curved space introduced by Weeks and another discovered by Best. These examples illustrate how future satellite-based observations of the microwave background can determine the full geometry of the universe. @S0556-2821~98!02124-9# PACS number~s!: 98.70.Vc, 98.80.Hw From the zebra’s stripes to the leopard’s spots, the animal kingdom displays a diversity of coat patterns. Following the innovative ideas of Turing @1#, mathematical biologists have posed and partly answered the question of how the leopard got its spots. The fluctuation of enzymes diffusing through the developing embryo can lead to the spatial pattern formation displayed by animal coats. Both the geometry and size of the animal exert a strong influence on differentiating patterns. For instance, the broad cylindrical shape of the leopard’s body favors spots while the tapered tail induces stripes @2#. Remarkably, these diverse features can arise from the properties of simple solutions to second-order partial differential equations on the geometry and topology appropriate for animal limbs, tails, or bodies. 1
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TL;DR: In this paper, the authors present gravitation as a theory in which the coordinates are distances and velocities between galaxies and show that there are three possibilities for the universe to expand: decelerating, constant and accelerating, and it is shown that the Universe is now in the latter phase.
Abstract: We present gravitation as a theory in which the coordinates are distances and velocities between galaxies. We show that there are three possibilities for the Universe to expand: decelerating, constant and accelerating, and it is shown that the Universe is now in the latter phase. Assuming "Omega"_m=0.245, the time at which the Universe goes over from a decelerating to an accelerating expansion, occurs at 8.5 Gyr ago, at which time the cosmic radiation temperature was 146K. The theory predicts also that now there is a positive pressure, p=0.034g/cm^2, in the Universe. Although the theory has no cosmological constant, we extract from it its equivalence and show that "Lambda"=1.934x10^{-35}s^{-2}, which is in excellent agreement with measurements. It is also shown that the three-dimensional space of the Universe is Euclidean. Comparison with general relativity theory is finally made and it is shown that the classical experiments as well as the gravitational radiation prediction follow from the present theory, too.
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TL;DR: In this article, the authors consider a model in which local Lorentz invariance is spontaneously broken in the very early universe, and in this epoch the speed of light undergoes a first or second order phase transition to a value ~ 30 orders of magnitude smaller, corresponding to the presently measured speed.
Abstract: It is generally believed that inflationary cosmology explains the isotropy, large scale homogeneity and flatness as well as predicting the deviations from homogeneity of our universe. We show that this is not the only cosmology which can explain successfully these features of the universe. We consider anew and modify a model in which local Lorentz invariance is spontaneously broken in the very early universe, and in this epoch the speed of light undergoes a first or second order phase transition to a value ~ 30 orders of magnitude smaller, corresponding to the presently measured speed of light. Before the phase transition at a time t ~ t_c, the entropy of the universe is reduced by many orders of magnitude, allowing for a semiclassical quantum field theory calculation of a scale invariant fluctuation spectrum. After the phase transition has occurred, the radiation density and the entropy of the universe increase hugely and the increase in the entropy follows the arrow of time determined by the spontaneously broken direction of the vev _0. This solves the enigma of the arrow of time and the second law of thermodynamics. A new calculation of the primordial Gaussian and adiabatic fluctuation spectrum is carried out, leading to a scale invariant scalar component of the power spectrum. We argue that there are several attractive features of VSL theory compared to standard inflationary theory, and that it provides an alternative cosmology with potentially different predictions.
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TL;DR: In this paper, the authors consider the brane gas picture of the early universe and show that a moving 3-brane, which they identify with our universe, can inflate even though it is radiation-dominated.
Abstract: We consider the brane gas picture of the early universe. At later stages, when there are no winding modes and the background is free to expand, we show that a moving 3-brane, which we identify with our universe, can inflate even though it is radiation-dominated. The crucial ingredients for successful inflation are the coupling to the dilaton and the equation of state of the bulk. If we suppose the brane initially forms in a collision of higher-dimensional branes, then the spectrum of primordial density fluctuations naturally has a thermal origin.
TL;DR: The quantum origin of the universe due to a positive cosmological constant is studied in this paper, where it is shown that the universe can be viewed as a supercomputing system.
Abstract: The quantum origin of the Universe due to a positive cosmological constant is studied.
TL;DR: In this paper, the authors analyse the chemical history of the dark age through the creation of the primordial nuclei to the formation of the first atoms and molecules, and describe the consequences of the molecular formation on the birth of the proto-objects.
TL;DR: The universe is filled with neutrinos as discussed by the authors, which were created less than one second after the Big Bang and remain in the universe today because they interact very weakly with matter.
Abstract: IF WE look deep into the universe, we see stars and galaxies of all shapes and sizes. What we do not see, however, is that the universe is filled with particles called neutrinos. These particles – which have no charge and have little or no mass – were created less than one second after the Big Bang, and large numbers of these primordial low-energy neutrinos remain in the universe today because they interact very weakly with matter. Indeed, every cubic centimetre of space contains about 300 of these uncharged relics.
TL;DR: In this article, it is shown that the first law of thermodynamics can be applied to the de Sitter universe to relate its vacuum energy, pressure, entropy of horizon, chemical potential, etc., when the cosmological constant changes due to fluctuation of the vacuum or other reasons.
Abstract: It is shown that the first law of thermodynamics can be applied to the de Sitter universe to relate its vacuum energy, pressure, entropy of horizon, chemical potential, etc., when the cosmological constant changes due to the fluctuation of the vacuum or other reasons. The second law should be reformulated in the form that the spontaneous decay of the vacuum never makes the entropy of the de Sitter universe decrease. The third law of thermodynamics, applying to the de Sitter universe, implies that the cosmological constant cannot reach zero by finite physical processes. The relation to the holographic principle is also briefly discussed.
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TL;DR: In this article, the authors explore a model of the universe in which dark energy is modelled explicitely with both a dynamical quintessence field (with a double exponential self-interaction potential) and a cosmological constant.
Abstract: In this work we explore a model of the universe in which dark energy is modelled explicitely with both a dynamical quintessence field (with a double exponential self-interaction potential) and a cosmological constant. For a given region of the parameter space, our results confirm the possibility of a collapsing universe, which is necessary for an adequate definition of both perturbative quantum field and string theories. We have also reproduced the measurements of modulus distance from supernovae with good accuracy.
TL;DR: In this article, it was shown that primordial black holes in Brans-Dicke theory cannot grow at the same rate as the size of the cosmological particle horizon.
Abstract: We investigate spherically symmetric self-similar solutions in Brans-Dicke theory. Assuming a perfect fluid with the equation of state $p=(\ensuremath{\gamma}\ensuremath{-}1)\ensuremath{\mu}(1l~\ensuremath{\gamma}l2),$ we show that there are no nontrivial solutions which approach asymptotically to the flat Friedmann-Robertson-Walker spacetime if the energy density is positive. This result suggests that primordial black holes in Brans-Dicke theory cannot grow at the same rate as the size of the cosmological particle horizon.
TL;DR: In this paper, a quantum theory of the universe is proposed, which predicts the observed dimensions of the non-homogeneities of matter density and the amplitude of fluctuations of the cosmic background radiation temperature in the universe.
Abstract: Old and new puzzles of cosmology are reexamined from the point of view of the quantum theory of the universe developed here. It is shown that in the proposed approach the difficulties of the standard cosmology do not arise. The theory predicts the observed dimensions of the non-homogeneities of matter density and the amplitude of fluctuations of the cosmic background radiation temperature in the Universe and points to a new quantum mechanism of their origin. The large-scale structure in the Universe is explained by the growth of non-homogeneities which arise from primordial quantum fluctuations due to the finite width of the quasistationary states. The theory allows one to obtain the value of the deceleration parameter, which is in good agreement with the recent SNe Ia measurements. It explains the large value of the entropy of the Universe and describes other parameters.
TL;DR: In this article, the authors investigated the effect of inhomogeneities on the volume expansion of the universe, and they found that inhomogeneity makes the expansion slower than that of the background universe when they can be regarded as small fluctuations in the background.
Abstract: In order to investigate the effect of inhomogeneities on the volume expansion of the universe, we study a modified Swiss-cheese universe model. Since this model is an exact solution of Einstein's equations, we can get insight into the nonlinear dynamics of an inhomogeneous universe from it. We find that inhomogeneities make the volume expansion slower than that of the background Einstein--de Sitter universe when they can be regarded as small fluctuations in the background universe. This result is consistent with the previous studies based on the second order perturbation analysis. On the other hand, if the inhomogeneities cannot be treated as small perturbations, the volume expansion of the universe depends on the type of fluctuations. Although the volume expansion rate approaches the background value asymptotically, the volume itself can be finally arbitrarily smaller than the background one and can be larger than that of the background, but there is an upper bound on it.
TL;DR: In this paper, the authors consider the fate of the observable universe in the light of the discovery of a dark energy component to the cosmic energy budget and examine the constraints on phenomena that may prevent the eternal acceleration of our patch of the universe.
Abstract: We consider the fate of the observable universe in the light of the discovery of a dark energy component to the cosmic energy budget. We extend results for a cosmological constant to a general dark energy component and examine the constraints on phenomena that may prevent the eternal acceleration of our patch of the universe. We find that the period of accelerated cosmic expansion has not lasted long enough for observations to confirm that we are undergoing inflation; such an observation will be possible when the dark energy density has risen to between 90% and 95% of the critical. The best we can do is make cosmological observations in order to verify the continued presence of dark energy to some high redshift. Having done that, the only possibility that could spoil the conclusion that we are inflating would be the existence of a disturbance (the surface of a true vacuum bubble, for example) that is moving toward us with sufficiently high velocity, but is too far away to be currently observable. Such a disturbance would have to move toward us with speed greater than about $0.8c$ in order to spoil the late-time inflation of our patch of the universe and yet avoid being detectable.
TL;DR: In this paper, the authors used a Riemannian four-dimensional presentation for gravitation in which the coordinates are distances and velocity rather than the traditional space and time, and solved the field equations and showed that there are three possibilities for the universe to expand.
Abstract: We use a Riemannian four-dimensional presentation for gravitation in which the coordinates are distances and velocity rather than the traditional space and time. We solve the field equations and show that there are three possibilities for the Universe to expand. The theory describes the Universe as having a three-phase evolution with a decelerating expansion, followed by a constant and an accelerating expansion, and it predicts that the Universe is now in the latter phase. It is shown, assuming Ωm = 0.245, that the time at which the Universe goes over from a decelerating to an accelerating expansion, occurs at 8.5 Gyr ago, at which time the cosmic radiation temperature was 146K. Recent observations show that the Universe's growth is accelerating. Our theory confirms these recent experimental results. The theory predicts also that now there is a positive pressure in the Universe. Although the theory has no cosmological constant, we extract from it its equivalence and show that Λ = 1.934 × 10-35 s-2. This value of Λ is in excellent agreement with measurements. It is also shown that the three-dimensional space of the Universe is Euclidean, as the Boomerang experiment shows.
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TL;DR: In this paper, the authors focus on the cosmological implications of a positively curved brane world evolving in the background of a topological anti-de Sitter black hole and show that the bulk black hole will typically induce either an asymptotically de Sitter ''bounce'' universe or a big bang/big crunch FRW universe depending on a critical value of mass.
Abstract: In view of our accelerating universe, one of the outstanding theoretical issues is the absence of a quantum-gravitational description of de Sitter space Although speculative, an intriguing circumvention may be found in the realm of brane-world scenarios; where the physical universe can be interpreted as a non-critical 3-brane moving in a higher-dimensional, static bulk In this paper, we focus on the cosmological implications of a positively curved brane world evolving in the background of a ``topological'' anti-de Sitter black hole (ie, Schwarzschild-like but with an arbitrary horizon topology) We show that the bulk black hole will typically induce either an asymptotically de Sitter ``bounce'' universe or a big bang/big crunch FRW universe, depending on a critical value of mass Interestingly, the critical mass is only non-vanishing in the case of a spherical horizon geometry We go on to provide a holographic interpretation of this curiosity
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TL;DR: In this paper, the authors describe a mission to detect these Gravitational Echos Across Time (GREAT) that would open up a new window on the very early universe.
Abstract: We are surrounded by radiation that originated from the big bang. It has traveled to us from the farthest reaches of the Universe, carrying with it an unaltered record of the beginning of time and space. The radiation is in the form of gravitational waves - propagating ripples in the curvature of spacetime. We describe a mission to detect these Gravitational Echos Across Time (GREAT) that would open up a new window on the very early universe. By studying the gravitational echoes of the big bang we will gain insight into the fundamental structure of matter, gravity, and how the Universe formed.