弯曲时空中的热平衡

讨论了弯曲时空的一种特殊情况--稳态时空中的热平衡条件,利用普朗克黑体辐射定律和广义相对论,得出了两系统通过辐射而达到热平衡时坐标温度相等,但固有温度不相等的结论.     

宇宙极早期的剧涨

 在为数众多的宇宙演化理论中,目前为大多数科学家所接受的就是热宇宙标准模型,即我们通常所说的大爆炸学说.大爆炸学说是建立在爱因斯坦的广义相对论和近代物理理论基础上的,它得到了与观察事实相符合的一系列结论,譬如:它可解释目前的宇宙处在膨胀之中和宇宙中氦的丰度等,并预言了宇宙中存在3K微波背景辐射(已于1965年由彭齐斯和威尔逊证实,他们俩为此荣获了1978年度的诺贝尔物理学奖金).但是,就像通常刚建立的物理理论一样,随着研究的进一步深入,科学家们发现了它的几个致命缺陷,这些缺陷可归纳为以下几点:一、视界问题.这是在解释可观察宇宙的大尺度均匀性时所遇到的问题.在微波背景辐射的研究中已证实宇宙有一个非常重要的特征量--宇宙等效温度,简称宇宙温度.根据微波背景辐射中已测出的辐射能量密度及其频率,再利用普朗克黑体辐射公式,就可知道当今的宇宙温度为2.7K;这说明了宇宙在大尺度范围内是处在热平衡之中的(否则就没有宇宙温度可言).但大爆炸理论诉告我们:在混沌初开时,宇宙是一个灼热的奇点.但随着爆炸过后,需要多长时间才能达到热平衡状态呢?     

物理学中的宇与宙

 一、物理与宇宙 宇宙,爱因斯坦称时空。二千多年前,中国《淮南子》称:四方上下曰宇,古往今来曰宙。     

从2017诺贝尔物理学奖展望新加坡未来科学的发展方向

<正>2017年诺贝尔物理学奖颁给了3位在引力波领域作出突出贡献的美国物理学家,他们分别为麻省理工学院雷纳·韦斯(Rainer Weiss)、加州理工学院基普·索恩(Kip S.Thorne)和巴里·巴里什(Barry C.Barish)。引力波是一百年前爱因斯坦广义相对论所预言的一种以光速传播的时空波动,如同石头丢进水里产生的波纹一样,被视为宇宙中的"时空涟漪"。在广义相对论中,引力产生的效果又可以用时空扭曲解释。广义相对论场方程,是一个和时空度规有关的二阶非线性偏微分方程。探测到的引力波是通过光的干涉探测器感知空间被扭曲的微小变化。空间扭曲引发光的干涉条纹发生轻微抖动。引力波可能是宇宙公认的传播媒介,探     

诱导引力理论中宇宙场的三次量子化

诱导引力与爱因斯坦引力难以用目前的实验来区分.在研究诱导引力的宇宙量子场论时,通过对宇宙场的三次量子化,发现在希格斯场的真空期待值附近,即使无任何其它物质场存在,宇宙也可以从“无”(nothing)通过量子隧道过程而创生,其创生宇宙遵从Planck分布.但这种从无到有的宇宙创生过程是无法从真空经典爱因斯坦引力理论中得到的. 关键词：     

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采用光学多通道分析仪等设备对532nm YAG激光诱导产生的Al等离子体光谱进行了时空分辨测量,得到了等离子体时空分辨光谱。利用局部热平衡(LTE)模型和谱线的Stark展宽计算得到了等离子体电子温度和电子密度的时空演化曲线,获得了与文献[9～11]一致的结果。     

爱因斯坦与宇宙常量

1917年，爱因斯坦发表了他的关于整个宇宙时空结构的理论——广义相对论。同时，他猜想宇宙是静止的，但是他的广义相对论方程的解却是时间的函数，也就是说，从广义相对论方程来看，宇宙是运动的，为了解决这一矛盾，爱因斯坦在方程中增加了新的一项——宇宙常数项，修改了他的方程。可是后来的天文学研究发现宇宙其实不是静止的，而是向外膨胀的，爱因斯坦很后悔在方程中增加了宇宙常数项，他也因此非常遗憾地错过了预言宇宙的膨胀。     

宇宙背景辐射的短波畸变

1987年2月23日,日本名古屋大学和美国加利福尼亚大学伯克利分校组成的合作小组.利用当天从日本发射的试探火箭,对宇宙背景辐射进行了高精确度测量.结果发现宇宙背景辐射在亚毫米波段大大偏离了黑体辐射.这与1981年Herbert Gush和 Mark Halpern报道的结果很相似. 根据大爆炸理论模型,宇宙背景辐射的光子产生于高红移时期.红移公式为1 Z=λ0/λe,其中λ0和λe分别是观测到的和发射的波长.在宇宙的早期,辐射与物质处于热平衡,产生的光子具有黑体辐射谱.到Z<10 6时,各种产生光子以维持热平衡的过程的产生率将变得不足以维持辐射的黑体谱.但是…     

探索的历程——引力波的发现

正2016年11日是个值得纪念的日子,这一天美国科学家对外宣布探测到引力波,这是人类首次直接探测到了引力波,同时也验证了已有百年的爱因斯坦广义相对论预言的引力波的存在。这次成果是分别由位于美国路易斯安那州列文斯顿和华盛顿州汉福德的激光干涉引力波观测台(LIGO)的一对探测器探测到的。下面就让我们回顾一下围绕引力波发生的那些事……图1,1916年6月,爱因斯坦预测了宇宙中的涟漪。根据广义相对论,引力是质量巨大物体周围时空的扭曲。爱因斯坦认为时空会产生涟漪并产生"引力波"并以光     

Anti-de Sitter时空中黑洞量子熵的发散结构

用“brick- wall”模型研究了Anti-de Sitter时空中起源于电磁和引力场的黑洞量子熵的发散结构, 结果表明量子熵由线性发散项和对数发散项构成. 如果平衡温度选为Hawking温度，固有截断替代坐标截断，则线性发散项可化为正比于事件视界面积的形式；而对数发散项不仅依赖于黑洞的特征，也依赖于场的自旋，由于此项的存在，自旋场的贡献不再与标量场的贡献成正比. 关键词： 发散结构 黑洞熵 AdS时空 电磁和引力场     

A Non-Singular Universe with Vacuum Energy

A model for the universe based on the back-reaction effects of quantum fields at finite temperature in the background of Robertson-Walker spacetime and in the presence of a non-zero cosmological constant is constructed. We discuss the vacuum regime in the light of the results obtained through previous studies of the back-reaction of massless quantum fields in the static Einstein universe, and we argue that an adiabatic vacuum state and thermal equilibrium is achieved throughout this regime. Critical density is maintained naturally from the very early stages as a consequence of back-reaction effect of the vacuum fluctuations of quantum fields. Results show that such a model can explain many features of the early universe as well as the present universe. The model is free from the basic problems of the standard Friedmann cosmology, and is non-singular but involves a continuous creation of energy at a rate proportional to the size of the universe, which is lower than that suggested by the steady-state cosmology.     

Is thermodynamics of the universe bounded by event horizon a Bekenstein system?

In this brief communication, we have studied the validity of the first law of thermodynamics for the universe bounded by event horizon with two examples. The key point is the appropriate choice of the temperature on the event horizon. Finally, we have concluded that universe bounded by the event horizon may be a Bekenstein system and Einstein?s equations and the first law of thermodynamics on the event horizons are equivalent.     

Are galaxies extending?

It is suggested that the recently observed size evolution of very massive compact galaxies in the early universe can be explained, if dark matter is in Bose–Einstein condensate. In this model the size of the dark matter halos and galaxies depends on the correlation length of dark matter and, hence, on the expansion of the universe. This theory predicts that the size of the galaxies increases as the Hubble radius of the universe even without merging, which agrees well with the recent observational data.     

Macroscopic Einstein equations to second order in the interaction constant

The present paper is a direct continuation of an earlier paper [JETP 83, 1 (1996)] devoted to the derivation of the macroscopic Einstein equations to within terms of second order in the interaction constant. Ensemble averaging of the microscopic Einstein equations and the Liouville equation for the random functions leads to a closed system of macroscopic Einstein equations and kinetic equations for one-particle distribution functions. The macroscopic Einstein equations differ from the classical equations in that their left-hand side contains additional terms due to particle interaction. The terms are traceless tensors with zero divergence. An explicit covariant expression for these terms is given in the form of momentum-space integrals of expressions dependent on one-particle distribution functions of the interacting particles of the medium. The given expressions are proportional to the cube of the Einstein constant and the square of the particle number density. The latter relationship implies that interaction effects manifest themselves in systems of very high density (the universe in the early stages of its evolution, dense objects close to gravitational collapse, etc.) Zh. éksp. Teor. Fiz. 112, 1153–1166 (October 1997)     

Models of the universe

In this paper a theory of models of the universe is proposed. We refer to such models ascosmological models, where a cosmological model is defined as an Einstein-inextendible Einstein spacetime. A cosmological model isabsolute if it is a Lorentz-inextendible Einstein spacetime,predictive if it is globally hyperbolic, andnon-predictive if it is nonglobally-hyperbolic. We discuss several features of these models in the study of cosmology. As an example, any compact Einstein spacetime is always a non-predictive absolute cosmological model, whereas a noncompact complete Einstein spacetime is an absolute cosmological model which may be either predictive or non-predictive. We discuss the important role played by maximal Einstein spacetimes. In particular, we examine the possible proper Lorentz-extensions of such spacetimes, and show that a spatially compact maximal Einstein spacetime is exclusively either a predictive cosmological model or a proper sub-spacetime of a non-predictive cosmological model. Provided that the Strong Cosmic Censorship conjecture is true, a generic spatially compact maximal Einstein spacetime must be a predictive cosmological model. It isconjectured that the Strong Cosmic Censorship conjecture isnot true, and converting a vice to a virtue it is argued that the failure of the Strong Cosmic Censorship conjecture would point to what may be general relativity's greatest prediction of all, namely,that general relativity predicts that general relativity cannot predict the entire history of the universe.     

Inhomogeneous dusty universes and their deceleration

Exact results stemming directly from Einstein equations imply that inhomogeneous universes endowed with vanishing pressure density can only decelerate, unless the energy density of the universe becomes negative. Recent proposals seem to argue that inhomogeneous (but isotropic) space–times, filled only with incoherent matter, may turn into accelerated universes for sufficiently late times. To scrutinize these scenarios, fully inhomogeneous Einstein equations are discussed in the synchronous system. In a dust-dominated universe, the inhomogeneous generalization of the deceleration parameter is always positive semi-definite implying that no acceleration takes place.     

Cawley's counterexample to Dirac's conjecture as a curved spacetime

Cawley's counterexample Lagrangian to Dirac's conjecture on dynamical systems is modified to a line element in curved spacetime, and the energy-momentum tensor corresponding to such a spacetime is found. The spacetime obtained satisfies the Einstein field equations and describes a three-dimensional matterfilled universe. It is further shown that such a universe cannot be filled up with other sources, such as a perfect fluid, a scalar field, or an electromagnetic field, without violating the Einstein field equations.     

An imbedding of spacetimes

It is shown that any two-dimensional spacetimes with compact Cauchy surfaces can be causally isomorphically imbedded into the two-dimensional Einstein’s static universe. Also, it is shown that any two-dimensional globally hyperbolic spacetimes are conformally equivalent to a subset of the two-dimensional Einstein’s static universe.