Showing papers on "Big Rip published in 1995"

The observational case for a low-density Universe with a non-zero cosmological constant

Abstract: OBSERVATIONS are providing progressively tighter constraints on cosmological models advanced to explain the formation of large-scale structure in the Universe. These include recent determinations of the Hubble constant1a¤-3 (which quantifies the present expansion rate of the Universe) and measurements of the anisotropy of the cosmic microwave background4,5. Although the limits imposed by these diverse observations have occasionally led to suggestions6 that cosmology is facing a crisis, we show here that there remains a wide range of cosmological models in good concordance with these constraints. The combined observations point to models in which the matter density of the Universe falls well below the critical energy density required to halt its expansion. But they also permit a substantial contribution to the energy density from the vacuum itself (a positive a¤˜cosmological constanta¤™), sufficient to recover the critical density favoured by the simplest inflationary models. The observations do not yet rule out the possibility that we live in an ever-expanding a¤˜opena¤™ Universe, but a Universe having the critical energy density and a large cosmological constant appears to be favoured.

Gravitational energy in the expanding universe

Abstract: The role of gravitational energy in the evolution of the universe is examined. In co-moving coordinates, calculation of the Landau-Lifshitz pseudotensor for FRW models reveals that: (i) the total energy of a spatially closed universe irrespective of the equation of state of the cosmic fluid is zero at all times, (ii) the total energy enclosed within any finite volume of the spatially flat universe is zero at all times, (iii) during inflation the vacuum energy driving the accelerated expansion and ultimately responsible for the creation of matter (radiation) in the universe, is drawn from the energy of the gravitational field. In a similar fashion, certain cosmological models which abandon adiabaticity by allowing for particle creation, use the gravitational energy directly as an energy source.

The energy of the Universe

Abstract: References to energy of the universe have focussed upon the matter contribution, whereas the conservation laws must include a gravitational contribution as well. The conservation laws as applied to FRW cosmologies suggest a zero total energy irrespective of the spatial curvature when the value of the cosmological constant is taken to be zero. This result provides a useful constraint on models of the early universe and lends support to currently studied theories of the universe arising as a quantum fluctuation of the vacuum.

Conditions for inflation in an initially inhomogeneous universe.

Abstract: Using a long wavelength iteration scheme to solve Einstein's equations near the big-bang singularity of a universe driven by a massive scalar field, we find how big initial quasi-isotropic inhomogeneities can be before they can prevent inflation to set in.

Physics: Concepts and Connections

Abstract: I. PRELUDE: OF STARS AND ATOMS. 1. The Way of Science: Experience and Ideas. 2. Atoms: The Nature of Things. II. THE NEWTONIAN UNIVERSE: A CLOCKWORK KINGDOM. 3. How Things Move: Galileo Asks the Right Questions. 4. Why Things Move As They Do. 5. The Universe According to Newton. III. TRANSITION TO THE NEW PHYSICS. 6. Conservation of Energy: You Can't Get Ahead -- 7. The Second Law of Thermodynamics: -- And You Can't Even Break Even. 8. Light and Electromagnetism. 9. Electromagnetic Waves. IV. THE POST-NEWTONIAN UNIVERSE: THE OBSERVER INTRUDES. 10. Relativity Theory. 11. The Universe According to Einstein. 12. Are We Alone? The Search for Extra-Terrestrial Intelligence. 13. Quantum Theory. 14. The Universe According to Quantum Theory. V. WITHIN THE ATOM: FIRE OF THE NUCLEUS, FIRE OF THE SUN. 15. The Nucleus and Radioactivity: A New Force. 16. Fusion and Fission: -- And a New Energy. 17. The Energy Future. 18. Quantum Fields: Relativity Meets the Quantum. Epilogue: Summing Up. Answers to Odd-Numbered Exercises and Problems. Glossary. Photo Credits. Index.

Quantum Cosmology and the Structure of Inflationary Universe

Abstract: In this review I consider several different issues related to inflation. I will begin with the wave function of the Universe. This issue is pretty old, but recently there were some new insights based on the theory of the self-reproducing inflationary universe. Then we will discuss stationarity of inflationary universe and the possibility to make predictions in the context of quantum cosmology using stochastic approach to inflation. Returning to more pragmatic aspects of inflationary theory, we will discuss inflationary models with $\Omega < 1$. Finally, we will describe several aspects of the theory of reheating of the Universe based on the effect of parametric resonance.

The Time Surface Term in Quantum Gravity

Abstract: The role of the time surface term in the ADM Hamiltonian formulation of general relativity is investigated. We show that the variable contained in the time surface term (the scale factor) plays the role of a time-like variable. The conjugated variable represents the energy density in the reduced phase space, where the Schr\"odinger like equation for a wave function is derived. The contribution from the surface term to the phase of the wave function allows us to define {\bf the phase time of the quantum Universe} so that it coincides with {\bf the proper time as an invariant interval} for the classical dust filled Universe. The quantum scenario of the evolution of the Universe filled in by the Weinberg-Salam fields is considered. The wave function of the early Universe as the functional from the Higgs fields and scale factor realizes the unitary irreducible representation of the SO(4,1) group. The elementary particle masses are determined by the angles of the scale--scalar field mixing.

A Model universe with variable dimension: Expansion as decrumpling

Abstract: We propose a model universe, in which the dimension of the space is a continuous variable, which can take any real positive number. The dynamics leads to a model in which the universe has no singularity. The difference between our model and the standard Friedman-Robertson-Walker models become effective for times much before the presently accepted age of the universe.

5D generalized inflationary cosmology

Abstract: We consider a 5D Kaluza-Klein type cosmological model with the fifth coordinate being a generalization of the invariant “historical” timeτ of the covariant theory of Horwitz and Piron. We distinguish between vacuum-, off-shell matter-, and on-shell matter-dominated eras as the solutions of the corresponding 5D gravitational field equations, and build an inflationary scenario according to which passage from the off-shell matter-dominated era to the on-shell one occurs, probably as a phase transition. We study the effect of this phase transition on the expansion rate in both cases of localO(4,1) andO(3,2) invariance of the extended (x µ,τ) manifold and show that it does not change in either case. The expansion of the model we consider is not adiabatic; the thermodynamic entropy is a growing function of cosmic time for the closed universe, and can be a growing function of historical time for the open and the flat universe. A complete solution of the 5D gravitational field equations is obtained for the on-shell matter-dominated universe. The open and the closed universe are shown to tend asymptotically to the standard 4D cosmological models, in contrast to the flat universe which does not have the corresponding limit. Finally, possible cosmological implications are briefly discussed.

Can the vacuum foam structure solve the flatness problem of a big bang universe

Abstract: It seems the vacuum foam structure of the very early universe, together with the traversable Lorentzian wormholes inherent in it, could provide a very large statistical entropy, which means that we may easily solve the flatness problem in a big bang universe without inflation.

Quantization of closed mini-superspace models as bound states

Abstract: The Wheeler-DeWitt equation is applied to closedk>0 Friedmann-Robertson-Walker metric with various combination of cosmological constant and matter (e.g., radiation or pressureless gas). It is shown that if the universe ends in the matter dominated era (e.g., radiation or pressureless gas) with zero cosmological constant, then the resulting Wheeler-DeWitt equation describes a bound state problem. As solutions of a nondegenerate bound state system, the eigen-wave functions are real (Hartle-Hawking). Furthermore, as a bound state problem, there exists a quantization condition that relates the curvature of the three space with the various energy densities of the universe. If we assume that our universe is closed, then the quantum number of our universe isN∼(Gk)−1∼10122. The largeness of this quantum number is naturally explained by an early inflationary phase which resulted in a flat universe we observe today. It is also shown that if there is a cosmological constant Λ>0 in our universe that persists for all time, then the resulting Wheeler-DeWitt equation describes a non-bound state system, regardless of the magnitude of the cosmological constant. As a consequence, the wave functions are in general complex (Vilenkin).

A static model of the universe

Abstract: It is shown that the observational data of cosmology and the universe evolution can be explained in the framework of static (non-expanding) models of the universe without singularity by introducing in the time part of the metrics the scale factor, dependent on time. The latter can be interpreted as a function of the light velocity evolution or the rate of cosmic time relative to the linear atomic time.

Inflation in ω-field cosmology

Abstract: In this paper, we shall apply the ω-field theory as first proposed by Yu13 to cosmology. Under the assumption that the spacetime geometry of the Universe is described by the Robertson-Walker metric and the matter tensor-consists only of theω-field, the Universe is found to follow a de Sitter Expansion. The horizon and flatness problems may thus be explained in a simple and natural way.

The Universe on a Large Scale

Abstract: To know the distribution of matter in the universe has been one of astronomers’ constant quests. It is pursued by studying more and more distant galaxies. The idea of a remote universe had been held since the middle of the eighteenth century. In the nineteenth century Herschel and Dreyer catalogued the many bright nebulae and noted how they were grouped. Recognition of the extragalactic realm of nature, mainly due to Shapley and Hubble in the years 1920–1930 (by the identification of Cepheids in Andromeda), like the discovery of the universal recession of galaxies by Hubble, opened the way to the development of extragalactic astronomy and to what would become observational cosmology. On extragalactic scales the galaxies, owing to the contrast in density that they represent (the mean density of our Galaxy within 10 kpc is approximately 2 × 10−24 g cm−3, while the mean density of the universe lies (probably) between 10−29 and 10−31g CM−3), are the most immediately discernible entities. Until recently they were thought to provide a reliable indicator of matter on a large scale, and their study led to the idea of a globally homogeneous and isotropic universe.

The Secret Melody: And Man Created the Universe

Abstract: 1: Past Universes. 2: From the Milky Way to the Universe. 3: The Actors in the Drama: The Galaxies and the Space-Time Couple. 4: The Big Bang Today. 5: The History Book of the Universe. 6: The Invisible and the Fate of the Universe. 7: An Accidental or Necessary Universe?. 8: God and the Big Bang. 9: The Secret Melody. 10: Appendix A: Light and the Doppler Effect. 11: Appendix B: The Elasticity of the Space-Time Couple. 12: Appendix C: Black Holes. 13: Appendix D: The Uncertainty Principle in Quantum Mechanics. 14: Appendix E: The Cosmological Parameters and the Evolution of the Universe. 15: Glossary. 16: Bibliography. 17: Index

Density perturbations in a cosmological de Donder gauge

Abstract: Density perturbations are considered during the radiation-dominated and the dust-dominated periods of the expanding universe. The perturbations are taken to have spherical symmetry and the investigation is carried out in the de Donder gauge. In order to guarantee the energy-momentum conservation of the perturbation in the de Donder gauge a compatibility condition is obtained. Equations for the propagation of a spherically symmetric perturbation in linear approximation on a FRW cosmological background are presented. It turns out that the evolutiontendency of the formation is mainly predicted by the state of the cosmic background. A radiation-dominated universe does not stimulate growth processes; the perturbation will be in a frozen state or it will diffuse. It is found that the dust-dominated universe stimulates the perturbation mass to grow. The rate of this cosmic affected growing process is proportional toR−1 (R being the scale factor of the universe), so that it seems that almost all galaxies were formed at the beginning of the present dust-dominated era.

The Stuff of the Universe; Dark Matter, Mankind and Anthropic Cosmology

Abstract: Why are we here? Part 1 Cosmic coincidences: how special is the universe? the geography of the universe two kinds of dark matter. Part 2 The stuff of the universe: the particle zoo halo stuff core stuff cosmic string gravity's telescopes the Lyman forest - emergence and evolution of galaxies. Part 3 The bespoke universe: tailor-made for man? or off the peg?

A Theory Approach for Creation of the Matter of Universe.

Abstract: We shall represent an approach for the creation of the matter of Universe in the framework of a Quantum Theory, established in an 8-dimensional space. The primitive matter was being created from the Primary Vacuum and it consisted of the deuterons atoms, neutrinos and photons, From these neutral elements the attractive centres were formed and in the final stage an extremely high mass density Universe was built, and successively, the Big-Bang occurred. The problems of particle dominance, of excess of the deuterons and of magnitude of the numbers of neutrinos, etc. are discussed. MIRAMARE TRIESTE August 1993 'On leave of absence from: Hochiminh City University, P.O. Box 657, Central Post Office, llochiniinh City, Vietnam.

The volume expansion rate and the age of the Universe

Abstract: Under four assumptions such that 1) Einstein’s theory of gravity is correct, 2) existence of foliation by geodesic slicing, 3) the trace of the extrinsic curvature, K, is negative at the present time in observed region, that is, the observed universe is now expanding, 4) the strong energy condition is satisfied, we show that Hv0t0 ≤ 1, where Hv ≡ −K/3 agrees with the Hubble parameter in the case of a homogeneous and isotropic universe, and t0 is the age of the Universe. If Hv0t0 > 1 is confirmed observationally, at least one of the four assumptions is incorrect. Key word: Hubble parameter

Formation of structure in the universe

Abstract: An introduction to modern theories for the origin of structure in the Universe is given. After a brief review of the growth of cosmological perturbations in an expanding Universe and a summary of some important observational results, the lectures focus on the inflationary Universe scenario and on topological defect models of structure formation. A summary of the theory and current observational status of cosmic microwave background temperature fluctuations is given. The final chapter is devoted to some speculative ideas concerning the connection between cosmology and fundamental physics, in particular to ways in which the singularity problem of classical cosmology may be resolved.

Cosmology: A First Course

Abstract: 1. Discovering the cosmos 2. The relativistic Universe 3. General relativity and the dynamics of the Universe 4. The primordial Universe 5. Galaxy formation Conclusion.