Cosmology and Civilizations

The available observational date and cosmological models indicate the possible existence of supercivilizations with ages of technological development 6-8 gigayears larger than on the Earth. The probability of their detection is probably conne with observations at wavelengths from 3 mcm to 3 mm, and also with the solution of the hidden mass problem and searches for multiconnection of the Universe.     

Cosmology and large telescopes

Assuming a large collecting area, a good angular resolution and a large field of view expected for the Japanese National Large Telescope (JNLT), we demonstrate that JNLT will provide a useful means of studying cosmological objects of interest. Among them I discuss how cosmological parameters and evolutionary effects can be obtained from redshift-magnitude relations, galaxy counts, distant supernovae, quasar properties, and large-scale structures. An advantage of near infrared observations is emphasized.Paper presented at the Symposium on the JNLT and Related Engineering Developments, Tokyo, November 29–December 2, 1988.     

The gas mass fraction in local and Z > 0.7 Galaxy Clusters: constraints on Cosmology

We present a study of the baryonic fraction in galaxy clusters aimed at constraining the cosmological parameters Ω_m, Ω_Lgr; and the ratio between the pressure and density of the `dark' energy, w. We use results on the gravitating mass profiles of a sample of nearby galaxy clusters observed with the BeppoSAX X-ray satellite (Ettori, De Grandi and Molendi, 2002)to set constraints on the dynamical estimate of Ω_m. We then analyze Chandra observations of a sample of eight distant clusters with redshift in the range 0.72 and 1.27 and evaluate the geometrical limits on the cosmological parameters Ω_m, Ω_Λ and w by requiring that the gas fraction remains constant with respect to the look-back time. By combining these two independent probability distributions and using a priori distributions on both Ω_b and H ₀ peaked around primordial nucleosynthesis and HST-Key Project results respectively, we obtain that, at 95.4 per cent level of confidence, (i) w < —0.54, (ii)Ω_m = 0.34^+0.11 _—0.05, Ω_Λ = 1.50^+0.24 _—1.13 for w = — 1 (corresponding to the case for a cosmological constant), and (iii) Ω_m = 1 —Ω_Λ = 0.33^+0.06 _—0.05 for a flat Universe. This paper summarizes the work in press at Astronomy & Astrophysics by Ettori, Tozzi and Rosati (astro-ph/0211335).     

Cosmology of Vacuum

Shortly the vacuum component of the Universe from the geometry point of view and from the point of view of the standard model of physics of elementary particles is discussed. Some arguments are given to the calculated value of the cosmological constant (Zel’dovich’s approximation). A new component of space vacuum (the gravitational vacuum condensate) is involved the production of which has fixed time in our Universe. Also the phenomenon of vacuum selforganization must be included in physical consideration of the Universe evolution.     

Chaos in Relativity and Cosmology

Chaos appears in various problems of Relativity and Cosmology. Here we discuss (a) the Mixmaster Universe model, and (b) the motions around two fixed black holes. (a) The Mixmaster equations have a general solution (i.e. a solution depending on 6 arbitrary constants) of Painlevé type, but there is a second general solution which is not Painlevé. Thus the system does not pass the Painlevé test, and cannot be integrable. The Mixmaster model is not ergodic and does not have any periodic orbits. This is due to the fact that the sum of the three variables of the system (α + β + γ) has only one maximum for τ = τ_m and decreases continuously for larger and for smaller τ. The various Kasner periods increase exponentially for large τ. Thus the Lyapunov Characteristic Number (LCN) is zero. The "finite time LCN" is positive for finite τ and tends to zero when τ → ∞. Chaos is introduced mainly near the maximum of (α + β + γ). No appreciable chaos is introduced at the successive Kasner periods, or eras. We conclude that in the Belinskii-Khalatnikov time, τ, the Mixmaster model has the basic characteristics of a chaotic scattering problem. (b) In the case of two fixed black holes M₁ and M₂ the orbits of photons are separated into three types: orbits falling into M₁ (type I), or M₂ (type II), or escaping to infinity (type III). Chaos appears because between any two orbits of different types there are orbits of the third type. This is a typical chaotic scattering problem. The various types of orbits are separated by orbits asymptotic to 3 simple unstable orbits. In the case of particles of nonzero rest mass we have intervals where some periodic orbits are stable. Near such orbits we have order. The transition from order to chaos is made through an infinite sequence of period doubling bifurcations. The bifurcation ratio is the same as in classical conservative systems. This revised version was published online in July 2006 with corrections to the Cover Date.     

Multidimensional Cosmology and Asymptotical AdS

A non-linear gravitational model with a multidimensional geometry and quadratic scalar curvature is considered. For certain parameter ranges, the extra dimensions are stabilized if the internal spaces have negative constant curvature. As a consequence, the 4-dimensional effective cosmological constant as well as the bulk cosmological constant become negative. The homogeneous and isotropic external space is asymptotically AdS₄. The connection between the D-dimensional and the 4-dimensional fundamental mass scales sets an additional restriction on the parameters of the considered non-linear models. This revised version was published online in July 2006 with corrections to the Cover Date.     

伽玛暴宇宙学的研究

伽玛射线暴(简称伽玛暴,gamma-ray burst (GRB))是一种来自宇宙空间中的伽玛射线波段流量突然增亮的现象,最早由Vela卫星在1967年发现.1997年人们通过余辉测得了伽玛暴的红移,从而确定了其宇宙学的起源.伽玛暴宇宙学包括用长暴的标准烛光关系限制暗能量和宇宙学参数,用长暴研究高红移的恒星形成率,研究金属丰度的演化、尘埃及量子引力等.     

Cosmology after COBE

The measured anisotropies in the temperature of the cosmic microwave background radiation (CMB) by the Cosmic Background Explorer (COBE) are consistent with models of gravitational collapse for the formation of large scale structure in the universe. The amplitude of cosmological fluctuations on the largest scales is fixed by COBE. From COBE's data it is also possible to test for the shape of the primordial spectrum. Statistical tests using COBE's two year data and based on the geometric characteristics of anisotropy spots taking into account cosmic variance and the relevant experimental details indicate that the primordial spectrum has a slope in the rangen = 0.8 – 1.3. Possible identification of hot and cold spots of cosmological origin is also given.Presented at the Fourth United Nations/European Space Agency Workshop on Basic Space Science. Cairo, Egypt, 27 June - 1 July 1994.     

Brans-Dicke Quantum Cosmology

By solving a Wheeler-De Witt ‘extended’ equation in the Brans-Dicke theory, we have found that the probability distribution predicts: i) An initial value for the Brans-Dicke scalar field φ ∼ ρ^1/2_VAC in the beginning of the inflation, where ρ_VAC is the vacuum density energy (this gives a planck mass ∼ ρ^1/4_VAC) ii) Large values for the Brans-Dicke parameter w. On the other hand it is shown that by taking into account the dynamical behaviour of φ and the matter scalar field σ we can formulate a ‘creation boundary condition’ where in the ‘beginning’ of the Universe (R =0, ‘nothing’ for some authors) we have a dynamical σ already ‘created’. This could be the energetic mechanism which makes Universe tunnels the potential barrier to evolve classically after. Besides we have found the possibility of a cosmological uncertainty principle. This revised version was published online in July 2006 with corrections to the Cover Date.     

Cosmology and a flat space

A theory of gravitation in a flat space is briefly described, which gives a completely new view on cosmological problems. Instead of expansion of the Universe, a contraction of bodies and clusters is obtained. This theory excludes the closed solutions as non-physical ones and gives a simple condition for the stability of gravitationally-bounded systems with respect to cosmological gravitational field.     

超新星宇宙学的观测与研究进展

超新星在宇宙学研究中起着重要的作用,2011年的诺贝尔物理学奖就颁给了利用Ia型超新星为探针发现宇宙加速膨胀的天文学家。首先,通过详细介绍超新星宇宙学研究的物理原理和发现宇宙加速膨胀的观测与研究,讨论了宇宙加速膨胀发现过程给予当前研究工作的启示。然后,回顾超新星宇宙学研究在近10多年来的进展和主要成果,分析了当前所面临的主要问题与挑战。最后,对国内外超新星宇宙学研究中超新星观测研究的大型项目情况进行了全面回顾与介绍,讨论和展望了超新星宇宙学研究工作的方向。     

等离子天体物理学与现代等离子体宇宙观

现代科学表明宇宙中99%以上的可观测物质都处于等离子体状态,从小尺度的微观粒子动力学集体过程与能量转换机制到大尺度的宇宙等离子天体结构状态与爆发活动现象,都是等离子天体物理学的研究课题.从宇宙演化历史、大尺度结构形成以及爆发活动现象等方面,系统地论述了等离子天体物理学在现代天文学发展以及现代等离子体宇宙观形成中的重要作用.同时,结合空间卫星科学探测研究及其对现代天文学的巨大影响,进一步阐述了地球磁层和日球层等空间等离子体实地探测研究在等离子天体物理学研究中所扮演的“天然实验室”的独特作用.     

Numerical Coincidences and `Tuning' in Cosmology

Fred Hoyle famously drew attention to the significance of apparent coincidences in the energy levels of the carbon and oxygen nucleus. This paper addresses the possible implications of other coincidences in cosmology. This revised version was published online in August 2006 with corrections to the Cover Date.     

Plasma Physics in Astronomy and Cosmology

We discuss some of the major areas in astronomy and cosmology where plasma physics is important: (1) origin of stars; (2) distortions of the microwave background radiation; (3) expansion rate of the Early Universe; (4) the magnetic fields and relativistic electrons in jets; (5) the collimation of jets; (6) the origin of stellar winds; (7) the origin of filaments and clouds not gravitationally bound; and (8) the origin of cosmic rays.     

The Atacama Cosmology Telescope

The proposed Atacama Cosmology Telescope (ACT) project is described. This multi-institution collaboration aims to produce arcminute-resolution and micro-Kelvin sensitivity maps of the microwave background temperature over 200 square degree of the sky in three frequency bands. We give a brief overview of the scientific motivations for such a map, followed by a design outline of our 6-m custom telescope, an overview of our proposed bolometer array detector technology, and site considerations and scan strategy. We also describe associated optical and X-ray galaxy cluster surveys.     

Cosmology in South Africa

This paper reviews research in theoretical cosmology in South Africa, providing an overview of the work that has been done and the groups involved in that work.     

Cosmology in a brane-universe

This contribution presents the cosmological models with extra dimensions that have been recently elaborated, which assume that ordinary matter is confined on a surface, called brane, embedded in a higher dimensional spacetime. This revised version was published online in July 2006 with corrections to the Cover Date.     

Initial Data Set for Cosmology

The method of conformal metric is used to find an analytic set of consistent initial data for the linearized Einstein field equations. We discuss the relation between independent degrees of freedom and perturbations. This revised version was published online in July 2006 with corrections to the Cover Date.     

Cosmology and cosmogony in a cyclic universe

In this paper we discuss the properties of the quasi-steady state cosmological model (QSSC) developed in 1993 in its role as a cyclic model of the universe driven by a negative energy scalar field. We discuss the origin of such a scalar field in the primary creation process first described by F. Hoyle & J. V. Narlikar forty years ago. It is shown that the creation processes which take place in the nuclei of galaxies are closely linked to the high energy and explosive phenomena, which are commonly observed in galaxies at all redshifts. The cyclic nature of the universe provides a natural link between the places of origin of the microwave background radiation (arising in hydrogen burning in stars), and the origin of the lightest nuclei (H, D, He³ and He⁴). It also allows us to relate the large scale cyclic properties of the universe to events taking place in the nuclei of galaxies. Observational evidence shows that ejection of matter and energy from these centers in the form of compact objects, gas and relativistic particles is responsible for the population of quasi-stellar objects (QSOs) and gamma-ray burst sources in the universe. In the later parts of the paper we briefly discuss the major unsolved problems of this integrated cosmological and cosmogonical scheme — the understanding of the origin of the intrinsic redshifts, and the periodicities in the redshift distribution of the QSOs.