Showing papers on "Particle horizon published in 1990"
TL;DR: In particular, if the mean density of the universe is as small as the baryon density inferred from standard cosmic nucleosynthesis calculations or as determined from typical dynamical studies of galaxies and galaxy clusters, then a value of Lambda large enough to produce a k = 0 universe would result in a substantially higher frequency of multiple-image lensing of quasars than has been observed so far as discussed by the authors.
Abstract: Inflationary cosmological theories predict, and some more general aesthetic criteria suggest, that the large-scale spatial curvature of the universe k should be accurately zero (i.e., flat), a condition which is satisfied when the universe's present mean density and the value of the cosmological constant Lambda have certain pairs of values. Available data on the frequency of multiple image-lensing of high-redshift quasars by galaxies suggest that the cosmological constant cannot make a dominant contribution to producing a flat universe. In particular, if the mean density of the universe is as small as the baryon density inferred from standard cosmic nucleosynthesis calculations or as determined from typical dynamical studies of galaxies and galaxy clusters, then a value of Lambda large enough to produce a k = 0 universe would result in a substantially higher frequency of multiple-image lensing of quasars than has been observed so far. Shortcomings of the available lens data and uncertainties concerning galaxy properties allow some possibility of escaping this conclusion, but systematic searches for a gravitational lenses and continuing investigations of galaxy mass distributions should soon provide decisive information. It is also noted that nonzero-curvature cosmological models can account for the observed frequency of galaxy-quasar lens systems and for a variety of other constraints.
190 citations
TL;DR: In this paper, a cosmological model in which the universe has its critical density and the gravitational and cosmology "constants"G and Λ are time-dependent is presented.
Abstract: A cosmological model in which the universe has its critical density and the gravitational and cosmological “constants”G and Λ are time-dependent is presented. The model may possibly solve the horizon and monopole problems. It predicts a perpetually expanding universe in whichG increases and Λ decreases with time in a manner consistent with conservation of the energy-momentum tensor. The model also allows the calculation of various cosmological parameters.
144 citations
TL;DR: In this paper, the authors analyzed spherically symmetric self-similar solutions to the Einstein equations and focused on those solutions that are asymptotically k = 0 Friedmann at large z values, and possess finite but perturbed density at the origin.
Abstract: The present analysis of spherically symmetric self-similar solutions to the Einstein equations gives attention to those solutions that are asymptotically k = 0 Friedmann at large z values, and possess finite but perturbed density at the origin. Such solutions represent nonlinear density fluctuations which grow at the same rate as the universe's particle horizon. The overdense solutions span only a narrow range of parameters, and resemble static isothermal gas spheres just within the sonic point; the underdense solutions may have arbitrarily low density at the origin while exhibiting a unique relationship between amplitude and scale. Their relevance to large-scale void formation is considered.
45 citations
TL;DR: A review of the evidence for large-scale motions of galaxies out to a distance of approximately 5000 km s-1 is given in this article, where the authors present a review of evidence for the large scale motion of galaxies.
Abstract: The expansion of the Universe can be retarded in localised regions within the Universe both by the presence of gravity and by non-gravitational motions generated in the post-recombination Universe. The motions of galaxies thus generated are called 'peculiar motions', and the amplitudes, size scales and coherence of these peculiar motions are among the most direct records of the structure of the Universe. As such, measurements of these properties of the present-day Universe provide some of the severest tests of cosmological theories. The author presents a review of the evidence for large-scale motions of galaxies out to a distance of approximately 5000 km s-1.
31 citations
TL;DR: In this paper, the authors studied the problem of nonsingular cosmological models based on a theory of gravitation in flat space-times and gave the solution of the model analytically.
Abstract: The study of nonsingular cosmological models [4] based on a theory of gravitation in flat space-times [1] is continued. For a radiation free universe the solution of the model is given analytically. Under the assumption that entropy cannot decrease the cosmological constant must be zero. At the beginning of the universe all energy is in the form of gravitation. The universe contracts. Matter and radiation are created out of gravitational energy and entropy is produced. The contraction stops and then the universe expands without limit. The creation of matter continues producing entropy but today the production of matter and entropy is negligible. The density parameter Ω0 ≈ 1, i.e. there must be “missing mass” in the universe. The “flatness” and the “homogeneity” problem are solved.
14 citations
TL;DR: In this article, the effects of shear on the occurrence of inflation were studied on the basis of a simple model for a spatially closed universe which enters an inflationary era, assuming that the universe enters a vacuumdominated phase in an abrupt transition that occurs everywhere at the same time, and the space-time geometries, before and after the phase transition, are matched to each other via the Lichnerowicz junction conditions.
Abstract: The effects of shear on the occurrence of inflation are studied on the basis of a simple model for a spatially closed universe which enters an inflationary era. It is assumed that the universe enters a vacuum‐dominated phase in an abrupt transition that occurs everywhere at the same time. The space‐time geometries, before and after the phase transition, are matched to each other via the Lichnerowicz junction conditions. The Einstein field equations are solved exactly for a viscous universe of the Kantowski–Sachs type. It is found that the inclusion of (positive) shear retards the occurrence of the vacuum phase transition. The magnitude of this effect depends on the mass of the universe at the time of the phase transition. For a universe with a mass of about 10 kg (which is a value usually associated with the mass of the region from which our universe originated), it is found that the inclusion of shear does not really have a large effect on the time at which the vacuum phase transition occurs. The generality of the results is also discussed.
10 citations
TL;DR: In this paper, the fluctuations in the cosmic microwave background radiation using the gauge invariant formalism were investigated for various cosmological models with the cosmologically constant, and the results showed that the fluctuations were stable.
Abstract: Thorough numerical calculations of the fluctuations in the cosmic microwave background radiation using the gauge invariant formalism are carried out for various cosmological models with the cosmological constant.
9 citations
TL;DR: In this paper, a model of a spatially finite universe with constant negative curvature and no boundary is presented, and the observational consequences of such a model are examined and it is shown that microwave isotropy and large scale structure with a characteristic lenghth of 100 −200 h −1 0 Mpc can be predicted.
8 citations
TL;DR: In this article, the conditions for the existence of a universe dominated by a scalar field in its early stages were analyzed in a homogeneous, Isotropic and spatially flat universe model.
Abstract: Analyzing the Klein-Gordon equation in a homogeneous, Isotropic and spatially flat universe model, we find the conditions for the existence of a universe dominated by a scalar field in its early stages.
7 citations
6 citations
TL;DR: In this article, the authors investigated the dynamics of the quantum universe under self-measurement in the framework of the path-integral approach to quantum theory of continuous measurements and the corresponding amplitude (propagator) was evaluated explicitly for a simple superspace model.
Abstract: The dynamics of the quantum universe under self-measurement is investigated in the framework of the path-integral approach to quantum theory of continuous measurements. The corresponding amplitude (propagator) is evaluated explicitly for a simple superspace model. It is shown that the picture of time evolution of the quantum universe naturally emerges as a result of its self-measurement. The Wheeler-DeWitt dynamics holds for small times when the effect of measurement can be neglected and time dependence disappears.
TL;DR: In this article, the optical depths of a radiation-dominated universe were derived for photoionization, Compton scattering, photon-matter pair production, photon photon scattering, and photon-photon pair production in interactions with the cosmic thermal background and baryonic matter.
Abstract: If the universe were radiation-dominated at redshifts greater than about 100-1000, eg, due to the presence of a small fraction of light particles in the dark matter, it would be optically thin in soft gamma-rays up to redshifts of 10,000 This is larger by an order of magnitude than for the matter-dominated universe X-rays and gamma-rays produced by cosmological high-energy processes are thus potentially observable up to z of about 10,000 Analytical formulas are derived for the optical depths of radiation-dominated universe due to photoionization, Compton scattering, photon-matter pair production, photon-photon scattering, and photon-photon pair production, in interactions with the cosmic thermal background and baryonic matter 29 refs
TL;DR: In this article, a study of matter-radiation universes under certain supplementary conditions specified in the introduction shows that the only model of this class compatible with observations is a parabolic universe which at the present time is almost the same as an Einstein-de Sitter model.
Abstract: A study of matter-radiation universes under certain supplementary conditions specified in the introduction shows us that the only model of this class compatible with observations is a parabolic universe which at the present time is almost the same as an Einstein-de Sitter model. The numerical values obtained for Hubble's constant, the age of the universe and the matter density at the present time are quite acceptable. We can also obtain some limits for the mass of neutrinos. The advantage of this parabolic model is that it gives the same results as thet
2/3 model at the present time and what is more could be used in studying problems of the formation of galaxies, after the recombination epoch, where matter and radiation have comparable importance.
TL;DR: In this paper, an interaction horizon is introduced that allows this scale to be determined for Robertson-Walker models for homogeneous isotropic universes, where the particle horizon defines causally connected regions.
Abstract: In homogeneous isotropic universes the particle horizon defines causally connected regions. For inflationary universes it is known that microphysics can interact coherently only on a much smaller scale. An interaction horizon is introduced that allows this scale to be determined for Robertson-Walker models. During inflation its upper bound is the event horizon.
TL;DR: In this article, the relation between the peculiar velocity and the density parameter in a one-dimensional inhomogeneous universe was derived for the case in which the density distribution is described by the Zeldovich solution.
Abstract: We derive the relation between the peculiar velocity and the density parameter in a one· dimensional inhomogeneous universe for the case in which the density distribution is described by the Zeldovich solution. We find that the simple relation obtained in the linear perturbation theory holds without any correction in spite of a fully non·linear nature of the problem. We also find that the inclusion of the cosmological constant in the present context does not change the above result.
TL;DR: In this paper, it was shown that the luminosity, the information and the frequency of a freely falling light source to an event horizon appear to the observer resting with respect to the horizon to decrease exponentially with a time scale which depends on the temperature of the horizon.
Abstract: It is proposed that the luminosity, the information and the frequency of a freely falling light source to an event horizon appear to the observer resting with respect to the horizon to decrease exponentially with a time scale which depends on the temperature of the horizon. This conclusion is valid not only for the Schwarzschild black hole, but also for the other black holes, the Rindler horizon, and the deSitter horizon.
01 Jan 1990
TL;DR: In this paper, it is shown that the existence of horizons of knowledge in any cosmological view of the universe is then tantamount to inherent observational limits imposed by acts of observation and theory itself.
Abstract: Unlike the usual situation with theoretical physics which is testable in the laboratory, in cosmological theories of the universe one faces the following problems: The observer is part of the system, the universe, and this system cannot be altered to test physical theory. Even though one can in principle consider any part of the observable universe as separate from the acts of observation, the very hypothesis of big bang implies that in the distant past, space-time regions containing current observers were part of the same system. One, therefore, faces a situation where the observer has to be considered as inherently a part of the entire system. The existence of horizons of knowledge in any cosmological view of the universe is then tantamount to inherent observational limits imposed by acts of observation and theory itself. For example, in the big bang cosmology the universe becomes opaque to radiation early on, and the images of extended distant galaxies merge for redshifts, z, of the order of a few. Moreover, in order to measure the distance of a remote galaxy to test any cosmological theory, one has to disperse its light to form a spectrum which would cause confusion with other background galaxies. Since the early universe should be described in quantum terms, it follows that the same problems regarding quantum reality and the role of the observer apply to the universe as a whole. One of the most fundamental properties of quantum theory, non-locality, may then apply equally well to the universe. Some of the problems facing big bang cosmology, like the horizon and flatness problems, may not then be preconditions on theoretical models but may instead be the manifestations of the quantum nature of the universe.
TL;DR: In this paper, the authors show that the understanding of the problem of time asymmetry can be reached from the hypothesis of typicalness of the universe, and they come to the following consequences: 1) the cosmological arrow of time, in general, should not coincide with the thermodynamic one, while the universe turns from the expanding phase to the contracting one.
Abstract: We show that the understanding of the problem of time asymmetry can be reached proceeding from the hypothesis of typicalness of the Universe. We come to the following consequences: 1) the cosmological arrow of time, in general, should not coincide with the thermodynamic one; 2) the thermodynamic arrow should not change its direction, while the Universe turns from the expanding phase to the contracting one; 3) CPT-invariance has to be violated. The last prediction, in principle, allows experimental verification.
TL;DR: In this article, a massive U (1) vector field A μ in a charged Robertson-Walker universe for k =+1, 0, and −1 can solve the initial singularity problem even at the level of classical gravity because the energy density becomes negative as the scale factor of the metric approaches zero.
TL;DR: In this paper, a model is proposed in which the universe evolves from vacuo and quantum fluctuations are taken into account, and the cosmological constant is shown to be inversely proportional to the squared radius of the De Sitter event horizon.
Abstract: A model is proposed in which the universe evolves from vacuo. At the Planck time a vacuum energy is considered and quantum fluctuations taken into account. These fluctuations cause the initial De Sitter event horizon to disappear and in this way the so-called cosmological constant also comes down to the actual value. This «constant» in fact results to be inversely proportional to the squared radius of the De Sitter event horizon. For increasingt, H(t)→ 0 and it is possible to match the proposed model with an FRW universe.
TL;DR: In this paper, a canonical time parameter corresponding to the synchronous reference frame is found for an isotropic cosmological model with relativistic gas, and Canonical quantization of the model is performed.
Abstract: A canonical time parameter corresponding to the synchronous reference frame is found for an isotropic cosmological model with relativistic gas. Canonical quantization of the model is performed. In the quantum theory, the radius of the Universe is an operator-valued function of time, whose values at different moments of time commute among themselves, and the state of the Universe itself does not change with time. In particular, this means that in experiments in which the radius of the Universe is measured, the presence of singularity is unavoidable within a finite interval of time in the past, and, for closed models, in the future.
TL;DR: In this article, it was shown that the exterior solutions of the Robertson-Walker metric in the Lyttleton-Bondi universe with cosmological constant are, in general, those space-times which represent stiff matter fluids in general relativity theory.
Abstract: It is shown that the exterior solutions of the Robertson-Walker metric in the Lyttleton-Bondi universe with cosmological constant are, in general, those space-times which represent stiff matter fluids in general relativity theory. This shows that a result stated by Varma and Roy is incorrect.
TL;DR: In this paper, a model for the early universe with the combined influence of scalar fields and vacuum polarization is discussed using phase plane portraints, and the results concern the probability of the birth of the universe, different de Sitter solutions and expressions for scalar perturbations.
Abstract: Models for the early Universe with the combined influence of scalar fields and vacuum polarization are discussed using phase plane portraints. The results concern the probability of the birth of the Universe, different de Sitter solutions and expressions for scalar perturbations.
TL;DR: Signals of the Quark-Gluon Plasma, supposedly a state of matter as a result of central collisions of two nuclei at ultrarelativistic energies, are investigated in this article with special emphasis on photons, photon pairs and muon pair production.
Abstract: Signals of the Quark-Gluon Plasma, supposedly a state of matter as a result of central collisions of two nuclei at ultrarelativistic energies are investigated with special emphasis on photons, photon pairs and muon pair production. Relics of the events at the primordial epochs of microseconds after the Big Bang origin of the universe, the Quark-Gluon Plasma condensing to hadrons, are investigated. The 7Li production rate is highlighted as a suitable boundary condition for early universe models.