Showing papers on "Big Rip published in 1998"

A Matter-Antimatter Universe?

Abstract: We ask whether the universe can be a patchwork consisting of distinct regions of matter and antimatter. We demonstrate that, after recombination, it is impossible to avoid annihilation near regional boundaries. We study the dynamics of this process to estimate two of its signatures: a contribution to the cosmic diffuse γ-ray background and a distortion of the cosmic microwave background. The former signal exceeds observational limits unless the matter domain we inhabit is virtually the entire visible universe. On general grounds, we conclude that a matter-antimatter symmetric universe is empirically excluded.

Quantum to classical transition for fluctuations in the early universe

Abstract: According to the inflationary scenario for the very early Universe, all inhomogeneities in the Universe are of genuine quantum origin. On the other hand, looking at these inhomogeneities and measuring them, clearly no specific quantum mechanical properties are observed. We show how the transition from their inherent quantum gravitational nature to classical behavior comes about — a transition whereby none of the successful quantitative predictions of the inflationary scenario for the present-day universe is changed. This is made possible by two properties. First, the quantum state for the spacetime metric perturbations produced by quantum gravitational effects in the early Universe becomes very special (highly squeezed) as a result of the expansion of the Universe (as long as the wavelength of the perturbations exceeds the Hubble radius). Second, decoherence through the environment distinguishes the field amplitude basis as being the pointer basis. This renders the perturbations presently indistinguishable from stochastic classical inhomogeneities.

Quantum creation of an open inflationary universe

Abstract: We discuss the dramatic difference between the description of the quantum creation of an open universe using the Hartle-Hawking wave function and the tunneling wave function. Recently Hawking and Turok have found that the Hartle-Hawking wave function leads to a universe with $\ensuremath{\Omega}=0.01,$ which is much smaller than the observed value of $\ensuremath{\Omega}.$ Galaxies in such a universe would be ${10}^{{10}^{8}}$ light years away from each other, and so the universe would be practically structureless. We argue that the Hartle-Hawking wave function does not describe the probability of the creation of the universe. If one uses the tunneling wave function for the description of the creation of the universe, then in most inflationary models the universe should have $\ensuremath{\Omega}=1,$ which agrees with the standard expectation that inflation makes the universe flat. The same result can be obtained in the theory of a self-reproducing inflationary universe, independently of the issue of initial conditions. However, there exist some models where $\ensuremath{\Omega}$ may take any value, from $\ensuremath{\Omega}g1$ to $\ensuremath{\Omega}\ensuremath{\ll}1.$

Can the Universe Create Itself

Abstract: The question of first-cause has troubled philosophers and cosmologists alike. Now that it is apparent that our universe began in a big bang explosion, the question of what happened before the big bang arises. Inflation seems like a very promising answer, but as Borde and Vilenkin have shown, the inflationary state preceding the big bang could not have been infinite in duration---it must have had a beginning also. Where did it come from? Ultimately, the difficult question seems to be how to make something out of nothing. This paper explores the idea that this is the wrong question---that that is not how the Universe got here. Instead, we explore the idea of whether there is anything in the laws of physics that would prevent the Universe from creating itself. Because spacetimes can be curved and multiply connected, general relativity allows for the possibility of closed timelike curves (CTCs). Thus, tracing backwards in time through the original inflationary state we may eventually encounter a region of CTCs---giving no first-cause. This region of CTCs may well be over by now (being bounded toward the future by a Cauchy horizon). We illustrate that such models---with CTCs---are not necessarily inconsistent by demonstrating self-consistent vacuums for Misner space and a multiply connected de Sitter space in which the renormalized energy-momentum tensor does not diverge as one approaches the Cauchy horizon and solves Einstein's equations. Some specific scenarios (out of many possible ones) for this type of model are described. For example, a metastable vacuum inflates producing an infinite number of (big-bang-type) bubble universes. In many of these, either by natural causes or by action of advanced civilizations, a number of bubbles of metastable vacuum are created at late times by high energy events. These bubbles will usually collapse and form black holes, but occasionally one will tunnel to create an expanding metastable vacuum (a baby universe) on the other side of the black hole's Einstein-Rosen bridge as proposed by Farhi, Guth, and Guven. One of the expanding metastable-vacuum baby universes produced in this way simply turns out to be the original inflating metastable vacuum we began with. We show that a Universe with CTCs can be stable against vacuum polarization. And it can be classically stable and self-consistent if and only if the potentials in this Universe are retarded---which gives a natural explanation of the arrow of time in our universe. Interestingly, the laws of physics may allow the Universe to be its own mother.

The end of the age problem, and the case for a cosmological constant revisited.

Abstract: The case for an open universe versus a flat universe with nonzero cosmological constant is reanalyzed, following new globular cluster dating results that now suggest a dramatically reduced lower limit on the age of the universe, which, for example, allow age consistency for a flat matter-dominated universe with a Hubble constant H0 ≤ 67 km s-1 Mpc-1. I incorporate not only the new age data but also updates on baryon abundance constraints and large-scale structure arguments. For the first time, the allowed parameter space for the density of nonrelativistic matter appears larger for an open universe than for a flat universe with cosmological constant, while a flat universe with zero cosmological constant remains strongly disfavored, in spite of the fact that it is now more consistent with the new age constraint. I argue that fundamental theoretical arguments favor a nonzero cosmological constant over an open universe. However, if either case is confirmed, the challenges posed for fundamental physics will be great.

The topology of the universe: the biggest manifold of them all

Abstract: Clues as to the geometry of the universe are encoded in the cosmic background radiation. Hot and cold spots in the primordial radiation may be randomly distributed in an infinite universe while in a universe with compact topology distinctive patterns can be generated. With improved vision, we could actually see whether the universe is wrapped into a hexagonal prism or a hyperbolic horn. We discuss the search for such geometric patterns in predictive maps of the microwave sky.

Is the Universe infinite or is it just really big

Abstract: The global geometry of the universe is in principle as observable an attribute as local curvature. Previous studies have established that if the universe is wrapped into a flat hypertorus, the simplest compact space, then the fundamental domain must be at least 0.4 times the diameter of the observable universe. Despite a standard lore that the other five compact, orientable flat spaces are more weakly constrained, we find the same bound holds for all. Our analysis provides the first limits on compact cosmologies built from the identifications of hexagonal prisms.

Computational Cosmology: From the Early Universe to the Large Scale Structure

Abstract: In order to account for the observable Universe, any comprehensive theory or model of cosmology must draw from many disciplines of physics, including gauge theories of strong and weak interactions, the hydrodynamics and microphysics of baryonic matter, electromagnetic fields, and spacetime curvature, for example. Although it is difficult to incorporate all these physical elements into a single complete model of our Universe, advances in computing methods and technologies have contributed significantly towards our understanding of cosmological models, the Universe, and astrophysical processes within them. A sample of numerical calculations (and numerical methods applied to specific issues in cosmology are reviewed in this article: from the Big Bang singularity dynamics to the fundamental interactions of gravitational waves; from the quark-hadron phase transition to the large scale structure of the Universe. The emphasis, although not exclusively, is on those calculations designed to test different models of cosmology against the observed Universe.

A lightweight universe

Abstract: How much matter is there in the universe? Does the universe have the critical density needed to stop its expansion, or is the universe underweight and destined to expand forever? We show that several independent measures, especially those utilizing the largest bound systems known—clusters of galaxies—all indicate that the mass-density of the universe is insufficient to halt the expansion. A promising new method, the evolution of the number density of clusters with time, provides the most powerful indication so far that the universe has a subcritical density. We show that different techniques reveal a consistent picture of a lightweight universe with only ∼20–30% of the critical density. Thus, the universe may expand forever.

Theorem for nonrotating singularity-free universes

Abstract: It is shown that all scalars built from the stress-energy tensor must have vanishing space-time average values in any nonrotating singularity-free universe in which the strong energy condition is satisfied. Application to the real universe, where observations seem to rule out such an ``empty'' universe, suggests that the hope of a reasonable realistic singularity-free cosmological model has to be abandoned.

Phase transitions in the universe

Abstract: During the past two decades, cosmologists turned to particle physics in order to explore the physics of the very early Universe. The main link between the physics of the smallest and largest structures in the Universe is the idea of spontaneous symmetry breaking, familiar from condensed matter physics. Implementing this mechanism into cosmology leads to the interesting possibility that phase transitions related to the breaking of symmetries in high energy particle physics took place during the early history of the Universe. These cosmological phase transitions may help us understand many of the challenges faced by the standard hot Big Bang model of cosmology, while offering a unique window into the very early Universe and the physics of high energy particle interactions.

Inhomogeneous Universe Models with Varying Cosmological Term

Abstract: The evolution of a class of inhomogeneous spherically symmetric universe models possessing a varying cosmological term and a material fluid, with an adiabatic index either constant or not, is studied.

The end of the old model Universe

Abstract: The ‘Big Bang’ model includes a few unknown numbers that determine the size, shape and future of the Universe. In the past few years our measurements of these free parameters have begun to rule out the old picture of a Universe dominated by cold dark matter. What will take its place?

Do we live in a low-density universe?

Abstract: There is a growing body of astronomical evidence that confirms the big bang model. In the hot big bang model, the density of the universe determines its geometry. The astronomical data suggest that the matter density of the universe is low. This implies that either there is some new form of matter or energy that does not cluster gravitationally (e.g. a cosmological constant) or that we live in an negatively curved universe.

Observable Relations in Relativistic Cosmology. II.

Abstract: Recent observations show that the assumption that the universe is isotropic and homogeneous, which forms part of current theories of the “expanding universe”, is probably not satisfied by the actual universe. This paper is an attempt to discover the type of relation which must hold between observable quantities if the theory of general relativity is applicable but if the assumption of isotropy and homogeneity is not made. It is first shown that Hubble's law, or something of a very similar character, must hold to a first approximation, independently of the distribution of matter. In order to relate the apparent recession of the nebulae to the distribution of matter, we must proceed to higher approximations in its relation to distance. With a certain relativistic representation of the universe in our neighbourhood, it is shown how the second approximation in the dependence of the apparent recession on distance can in fact be related to the mean density in our neighbourhood, whether or not the distribution is homogeneous or isotropic. The problem of expressing this relation in terms of quantities which are observable by astronomical methods is discussed, but is not completely solved.

Topology and the universe

Abstract: Topology may play an important role in cosmology in several different ways. First, Einstein's field equations tell us about the local geometry of the universe but not about its topology. Therefore, the universe may be multiply connected. Inflation predicts that the fluctuations that made clusters and groups of galaxies arose from random quantum fluctuations in the early universe. These should be Gaussian random phase. This can be tested by quantitatively measuring the topology of large-scale structure in the universe using the genus statistic. If the original fluctuations were Gaussian random phase then the structure we see today should have a spongelike topology. A number of studies by our group and others have shown that this is indeed the case. Future tests using the Sloan Digital Sky Survey should be possible. Microwave background fluctuations should also exhibit a characteristic symmetric pattern of hot and cold spots. The COBE data are consistent with this pattern and the MAP and PLANCK satellites should provide a definitive test. If the original inflationary state was metastable then it should decay by making an infinite number of open inflationary bubble universes. This model makes a specific prediction for the power spectrum of fluctuations in the microwave background which can be checked by the MAP and PLANCK satellites. Finally, Gott and Li have proposed how a multiply connected cosmology with an early epoch of closed timelike curves might allow the universe to be its own mother.

Flow instability in 3He-A as analog of generation of hypermagnetic field in early Universe

Abstract: It is now well-recognized that the Universe may behave like a condensed matter system in which several phase transitions have taken place Superconductors and the superfluid phases of 3He are condensed matter systems with useful similarities to the Universe: they both contain Bose fields (order parameter) and Fermions (quasiparticles) which interact in a way similar to the interaction of Higgs and gauge particles with fermions in particle physics This analogy allows us to simulate many properties of the cosmologically relevant physical (particle physics) vacuum in condensed matter, while direct experiments in particle physics are still far from realization Recently, the anomalous generation of momentum (called ``momentogenesis'') was experimentally confirmed in 3He: in the non-trivial background of a moving 3He vortex, quantum effects gave rise to the production of quasiparticles with momentum which were detected by measuring the force on the vortex This phenomenon is based on the same physics as the anomalous generation of matter in particle physics and bears directly on the cosmological problem of why the Universe contains much more matter than antimatter (``baryogenesis'') Here we report the experimental observation of the effect opposite to momentogenesis: the conversion of quasiparticle momentum into a non-trivial order parameter configuration or ``texture'' The corresponding process in a cosmological setting would be the creation of a primordial magnetic field due to changes in the matter content

The no-defect conjecture and its implications

Abstract: When the topology of the universe is non-trivial, there exist constraints on the network of topological defects that may appear during a phase transition in the early universe. Here we review the main results of two recent papers by Uzan and Peter concerning topological defects in a multiconnected universe: the no-defect conjecture, the evaluation of the redshift at which all the defects (if formed) have disappeared and the consequence on the cosmic microwave background.

A Dynamical Approach to a Self-similar Universe

Abstract: We write a non-relativistic Lagrangian for a hierar- chical universe. The equations of motion are solved numerically and the evolution of the fractal dimension is obtained for differ- ent initial conditions. We show that our model is homogeneous at the time of the last scattering, but evolves into a self-similar universe with a remarkably constant fractal dimension. We also show that the Hubble law is implied by this model and make an estimate for the age of the universe.

On the Hawking Turok solution to the Open Universe wave function

Abstract: Hawking and Turok have recently published a solution to the WKB "wave-function for the universe" which they claim leads in a natural way to an open universe as the end point of the evolution for a universe dominated by a scalar field. They furthermore argue that their solution a preferred solution under the rules of the game. This paper will, I hope, clarify their solution and the limits of validity of their argument.

Is There Cosmological Evidence for Additional Particles

Abstract: An extended cosmological model of the early Universe with additional antisymmetric tensor particles is described. The cosmological effects of the additional particles, namely, additional interactions of the early Universe plasma with the tensor particles, a shift of the early Universe temperature-time dependence and the total energy density increase are discussed. The efficiency of the tensor particle interactions with early Universe plasma components and their corresponding cosmological time and temperature are determined.

The inflationary Universe - from theory to observations.

Abstract: The inflationary Universe resolves some of the most outstanding issues of standard cosmology including the horizon and flatness problems and the origin of density fluctuations in the Universe. Inflationary models also predict the existence of a relic gravity wave background. Both gravity waves and density fluctuations induce fluctuations in the cosmic microwave background (CMB), the discovery of large angle anisotropies in the CMB having the scale invariant spectrum predicted by inflationary models has fuelled the hope that the inflationary scenario may indeed provide the correct description of the very early Universe. Upcoming large scale galaxy surveys (SDSS & 2dF) and CMB missions (MAP, Planck Surveyor) will further probe the inflationary scenario by throwing light on the origin and evolution of large scale structure in the Universe.

A quantum mechanical approach for a system of self-gravitating particles as applied to the universe

Abstract: A quantum mechanical formulation for the evolution of the present universe is made by considering it as a system of self-gravitating particles, fermionic in nature. Using a model single particle density distribution ρ(r) of its particles, singular at the origin, a compact expression for its radius R0 is obtained. A singular form of ρ(r) may be considered to be consistent with the Big Bang Theory of the universe. Assuming Mach's principle to hold good in the evolution of the universe, and taking the age of the present universe, τ0, to be 20 × 109 yr, we obtain the total mass of the universe M = (1.28 × 1023) M⊙, M⊙ being the solar mass, and the value , in extremely good agreement with the results obtained by others. Considering neutrinos to be the most possible candidate for the Dark Matter (DM), we find its mass to be ≃ 8 eV/c2, which also nicely agrees with the result as speculated by some recent calculations. Our theory reproduces the ratio of the neutrinos to the number of nucleons and the density of neutrinos in the present universe correctly.

Cosmology: A circumscribed Universe

Abstract: It would be hard to argue with Douglas Adams's statement, in The Hitch-Hiker's Guide to the Galaxy, that “Space is big”. But it may be a lot smaller than we thought. Evidence had come from the cosmic microwave background that the Universe is infinite, or at least not small compared with the distance we can see; but two astrophysicists have realized that this doesn't hold if the Universe has a low density. Such a so-called ‘open’ Universe can nevertheless be wrapped round on itself, allowing us to look at the back of our own heads, so to speak. We could soon find out for sure, as the scheduled satellites MAP and PLANCK search the microwave sky for identical rings.