哈勃常数和现代宇宙学

在介绍2009年格鲁伯宇宙学奖、简述现代观测宇宙学和哈勃常数的研究简史后,论述用哈勃空间望远镜研究哈勃常数和哈勃图在宇宙学中的应用.     

关于宇宙学常数问题的知识要点和几点思考

大爆炸宇宙学告诉我们,宇宙正在膨胀。如果我们的宇宙主要包含的是基本粒子型物质,那么宇宙将是减速膨胀。但是,对于今天我们观测到的宇宙来说,发现它在最近过去的几十亿年间却在加速膨胀!这预示着,宇宙中的主要能量形态不是基本粒子型物质,而是某种新的能量形态。对这种“新的”能量形态,其实科学家早有察觉和分析。它的最简单的可能性就是宇宙学常数。然而宇宙学常数的物理本质和内容却并不简单。这篇短文,就是主要介绍了宇宙学常数的一些基本知识和我们对它的一些思考。爱因斯坦方程中最自然出现的一项是宇宙学常数(简称cc)项,cc的值任意…     

GW170817与标准汽笛宇宙学

GW170817实现了基于“标准汽笛”的首次哈勃常数&;amp;lt;em&;amp;lt;H&;amp;lt;/em&;amp;lt;&;amp;lt;sub&;amp;lt;0&;amp;lt;/sub&;amp;lt;测量,开启了标准汽笛宇宙学的序幕。正在进行的双中子星并合引力波观测,有望在5年内测量&;amp;lt;em&;amp;lt;H&;amp;lt;/em&;amp;lt;&;amp;lt;sub&;amp;lt;0&;amp;lt;/sub&;amp;lt;到约2%精度,提供解决&;amp;lt;em&;amp;lt;H&;amp;lt;/em&;amp;lt;&;amp;lt;sub&;amp;lt;0&;amp;lt;/sub&;amp;lt;危机的独立而珍贵的数据。下一代的引力波实验,则将通过标准汽笛方法,精确测量宇宙膨胀速度和宇宙大尺度结构,限制暗能量状态方程,在宇宙学尺度上检验广义相对论。     

Solution to the Cosmological Constant Problem by Gauge Theory of Gravity

Based on geometry picture of gravitational gauge theory, the cosmological constant is determined theoreti-cally. The cosmological constant is related to the average energy density of gravitational gauge field. Because the energy density of gravltatlona] gauge field is negative, the cosmological constant is positive, which generates repulasive force on stars to make the expansion rate of the Universe accelerated. A rough estimation of it gives out its magnitude of the order of about 10^52m^-2, which is well consistent with experimental results.     

量子纠缠与宇宙学弗里德曼方程

量子纠缠作为量子信息理论中最核心的部分,代表量子态一种内在的特性,是微观物质的一种根本的性质,它是以非定域的形式存在于多子量子系统中的一种神奇的物理现象.熵也是量子信息理论的重要概念之一,纠缠熵作为量子信息的一个测度已经成为一种重要的理论工具,为物理学中的各类课题提供了新的研究方法.本文主要考虑量子纠缠的宇宙学应用,试图更好地从纠缠的角度来理解宇宙动力学.本文研究了量子信息理论的概念和宇宙学之间的深层联系,利用费米正则坐标和共形费米坐标构建了弗里德曼- 勒梅特-罗伯逊-沃尔克宇宙学弗里德曼方程和纠缠之间的联系.假设小测地球（a geodesic ball）的纠缠熵在给定体积下是最大的,可以从量子纠缠第一定律推导出弗里德曼方程.研究表明引力与量子纠缠之间存在着某种深刻的联系,这种联系对引力场方程的解是成立的.     

有关暗能量的一些话题

距在贵刊2004年发表的有关暗能量的两文[1,2]已4个年头,4年来,国内、外有关期刊发表了不少这一课题的文章.现就暗能量究竟是什么?宇宙中真的存在暗能量吗?和其他有关信息向读者做一简介.     

九十年代是宇宙学的黄金时代

 暂时我们还只有一些不完备的规律,这些规律制约着宇宙在所有非极端情形下的行为.现在看来这些规律都只是某个有待我们发现的统一理论的一部分.我们正在不断地取得进展,可能到本世纪末我们就能找到这个理论.     

宇宙年龄问题上的疑难

宇宙年龄是大爆炸宇宙学中的一个关键性的问题．文章对这问题的缘由、历史以及现状作了阐明．重点讨论了哈勃常数的实测值大小在宇宙年龄问题中的核心作用     

第六讲超弦理论与宇宙学的挑战

超弦理论从根本上改变了人们对时空的看法，时空在弦论中只是一种宏观体现．弦论中的非经典时空影响早期宇宙的发展，在一些观测宇宙学的实验中人们也许会发现弦论的效应，例如微波背景辐射的功率谱的反常．最近发现的暗能量也对弦论宇宙学提出了挑战．     

THE PROBLEM OF THE COSMOLOGICAL CONSTANT

The cosmological term is necessaritly vanishing in a conformal gravitational theory, and the sum of the induced cosmological constants of all the brocken gauge symmetries cancels the curvature of the background spacetime. Thus the sum of all the cosmological constants is vanishing when the background spacetime is Minkowskian. Furthermore, the spontaneous breaking of a gauge symmetry through the Higgs mechanism is always accompanied by a phase transition of the background spacetime.     

Solution to the Cosmological Constant Problem by Gauge Theory of Gravity

Based on geometry picture of gravitational gauge theory, the cosmological constant is determined theoreti-cally. The cosmological constant is related to the average energy density of gravitational gauge field. Because the energydensity of gravitational gauge field is negative, the cosmological constant is positive, which generates repulsive force onstars to make the expansion rate of the Universe accelerated. A rough estimation of it gives out its magnitude of theorder of about 10-52m-2, which is well consistent with experimental results.     

Vacuum Energy and the Economical Universe

We revisit a suggestion, first made by Haas and Jordan but often attributed to Tryon and others, that the universe could have zero net energy since a test body's positive rest energy is approximately cancelled out by its negative gravitational binding energy with respect to the rest of the matter in the universe. If the universe is not matter- but vacuum-dominated, as observations now indicate, then the balance between rest and binding energies is substantially altered. We consider whether this may make the Newtonian case for a universe from nothing more plausible than before.     

Elliptical Solutions to the Standard Cosmology Model with Realistic Values of Matter Density

We have examined a solution to the FRW model of the Einstein and de Sitter Universe, often termed the standard model of cosmology, using wide values for the normalized cosmic constant (Ω_∧) and spacetime curvature (Ω _k ) with proposed values of normalized matter density. These solutions were evaluated using a combination of the third type of elliptical equations and were found to display critical points for redshift z, between 1 and 3, when Ω_∧ is positive. These critical points occur at values for normalized cosmic constant higher than those currently thought important, though we find this solution interesting because the Ω_∧ term may increase in dominance as the Universe evolves bringing this discontinuity into importance. We also find positive Ω_∧tends towards attractive at values of z which are commonly observed for distant galaxies.     

A Quantum Universe and the Solution to the Cosmological Problems

We have found that the hierarchial problems appearing in cosmology are a manifestation of the quantum nature of the universe. The universe is still described by the same formulae that once hold at Planck's time. The universe is found to be governed by the Machian equation, GM = Rc ², where M and R are mass and radius of the universe. A Planck's constant xsfor different cosmic scales is provided. The status of the universe at different stages is shown to be described in terms of the fundamental constants (c, , G, , H) only. The concept of maximal (minimal) acceleration, power, temperature, etc., is introduced and justified.     

Conformal Invariance, Accelerating Universe and the Cosmological Constant Problem

We investigate a conformal invariant gravitational model which is taken to hold at early universe. The conformal invariance allows us to make a dynamical distinction between the two unit systems (or conformal frames) usually used in cosmology and elementary particle physics. In this model we argue that when the universe suffers phase transition, the resulting mass scale introduced by particle physics should have a variable contribution to vacuum energy density. This variation is controlled by the conformal factor which is taken as a dynamical field. We then deal with the cosmological consequences of this model. In particular, we shall show that there is an inationary phase at early times. At late times, on the other hand, it provides a mechanism which makes a large effective cosmological constant relax to a sufficiently small value. Moreover, we shall show that the conformal factor acts as a quintessence field that leads the universe to accelerate at late times.     

Vacuum driven accelerated expansion

It has been shown that an improved estimation of the quantum vacuum energy can yield not only theoretically acceptable but also experimentally realistic results. Our idea consists in a straightforward extraction of the gravitationally interacting part of the full quantum vacuum energy by means of gauge transformations. The implementation of this idea has been performed, in the background of a Friedmann‐Lemaître‐Robertson‐Walker geometry, by means of the euclidean version of the effective action formalism, in the language of Schwinger's proper time and Seeley‐DeWitt's heat kernel expansion.     

高红移Ⅰ_a型超新星的搜寻和宇宙的加速膨胀

观测研究表明,Ⅰａ型超新星可以作为宇宙距离测量的标准光源．天文学家还从近邻Ⅰａ型超新星光变的研究中得出可靠地确定其最高光度的方法．在此基础上,国际上两个相互竞争的研究集体经过几年的不懈努力,对高红移超新星进行了搜寻和观测．他们各自独立地得到了相同的结论：宇宙学常数Λ＞０,宇宙在加速膨胀．这项研究结果将对宇宙学,星系和大尺度结构的形成和演化的研究产生重要影响．更重要的是,它把所谓“宇宙学常数问题”提到我们面前,不再能够回避．而这一问题的解决将有可能带来基础研究上的重大突破     

Kinematics of a Spacetime with an Infinite Cosmological Constant

A solution of the sourceless Einstein's equation with an infinite value for the cosmological constant is discussed by using Inönü–Wigner contractions of the de Sitter groups and spaces. When , spacetime becomes a four-dimensional cone, dual to Minkowski space by a spacetime inversion. This inversion relates the four-cone vertex to the infinity of Minkowski space, and the four-cone infinity to the Minkowski light-cone. The non-relativistic limit c is further considered, the kinematical group in this case being a modified Galilei group in which the space and time translations are replaced by the non-relativistic limits of the corresponding proper conformal transformations. This group presents the same abstract Lie algebra as the Galilei group and can be named the conformal Galilei group. The results may be of interest to the early Universe Cosmology.