共查询到20条相似文献,搜索用时 93 毫秒
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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… 相似文献
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霍金的开放宇宙新理论 总被引:4,自引:0,他引:4
20世纪的天文观测表明,宇宙正处于膨胀的演化过程中.在时间上往过去反推,人们估计在100多亿年前宇宙是处于极其紧致极其炽热的所谓大爆炸奇性的状态.宇宙的演化必须服从爱因斯坦引力场方程.但是不同的初始状态会导致不同的演化.大爆炸奇性从何而来或者宇宙从何... 相似文献
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本文分析爱因斯坦相对论中关于一类没有相对运动的惯性系中刚性量杆的欧氏假定,以及相对性原理与宇宙学问的不协调。简单介绍我国学者提出的德西特不变的相对论,以及由暗宇宙启示的马赫原理。该相对论提供一个加速膨胀的观测宇宙所渐近趋向的模型。这里,不存在相对性原理与宇宙学问的不协调,存在一类相对于宇宙背景静止的优越惯性系,3维宇宙空间是闭的,宇宙常数起到惯性运动起源的作用。同时,这个模型提供观测宇宙的熵界,与全息原理的猜测一致,当曲率半径趋于无限时,这类优越惯性系仍然存在,不完全是爱因斯坦狭义相对论。 相似文献
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四、常曲率空时惯性原理及其宇宙学意义常曲率空时相对性原理和德西特不变的相对论如何面对暗宇宙的尖锐挑战?为什么我们的宇宙在加速膨胀,一定不渐近平坦,而很可能具有一个正的极小宇宙常数,渐近于德西特空时?而按照通常的处理,德西特空时却带来一系列疑难;极小而又为正的宇宙常数也带来极大困惑。通行的看法是把宇宙常数等同于量子理论中“真空”的能量。可是,这样得到的宇宙常数值比观测值大了一百二十几个量级;考虑种种可能修正、包括超对称等等,也还要大几十个量级。理论与观测之间如此大的差别,前所未有。根本问题出在哪里?通常的作法是考虑种种动力学模型、修改引力场方程,甚至借助量子引力等等。 相似文献
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1916年,爱因斯坦给出广义相对论场方程 其中R,g和丁分别是曲率、度规和能量-动量 张量,G是牛顿引力常数.然而,此方程不存在 静态宇宙解.在当时,宇宙的哈勃膨胀尚未被 观测到,爱因斯坦更倾向宇宙的静态模型.因 此,他在场方程左边又加上一项gμνλ,并把新引 入的未定参数L称为宇宙学常数.若λ为正,相 当于引入一等效于排斥力的项,它和引力的吸 引相抵消,使得有可能存在静态宇学解.当 星系红移测量表明宇宙并非静态之后,爱因斯 坦曾给韦尔写信说,如果字宙并非静态就去掉 宇宙学项. 可是,从现代量子场论看来,宇宙项很难去 掉.实际上,在场方程… 相似文献
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宇宙中的幽灵――暗物质 总被引:1,自引:0,他引:1
爱因斯坦曾经有一句名言:“宇宙最不可理解的是它竟然是可以理解的!”自从爱因斯坦写下他的可以理解宇宙的方程以及做出关于“宇宙是可以理解的”这个惊异的发现至今已有近一百年。 相似文献
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Eduardo V. Flores 《International Journal of Theoretical Physics》1993,32(8):1441-1444
The contribution of the quantum vacuum to the energy-momentum stress tensor in Einstein's field equations is very large. The observed cosmos is not in agreement with such a large term; thus, we require the presence of a cosmological constant to cancel this term. We discuss why this constant cannot originate from a quantum field or the gravitational field. We propose that this constant is physical evidence of the structure of space. The physical structure of space gives space an existence independent of the existence of matter and radiation. 相似文献
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第五讲暗能量和德西特时空 总被引:1,自引:0,他引:1
最近的天文观测表明,宇宙是在加速膨胀,而不是原来认为的减速膨胀.为解释加速膨胀,必须在宇宙的物质能量中引入暗能量这一成分,文章讨论了暗能量的可能侯选者,特别强调了宇宙常数问题、德西特时空问题以及和德西特时空相关的一些基本问题. 相似文献
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According to recent investigations of states of quantum fields, we
postulate that there exist negative energy photons in the universe.
With this assumption, we find a solution of Einstein's equation
without introducing the cosmological constant. A new and sizable
type Ia supernovae sample is employed to perform a fit with our
model and the conventional model. Both models can well account for
the current type Ia supernovae observation and they are not
distinguishable. With the new model, the cause of the accelerated
expansion of the universe and the mechanism of the negative pressure
existing in outer space can be explained in ordinary physical terms. 相似文献
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Superfluid condensation of neutrinos of cosmological origin at a low enough temperature can provide simple and elegant solution to the problems of neutrino oscillations and the accelerated expansion of the universe. It would give rise to a late time cosmological constant of small magnitude and also generate tiny masses for the neutrinos as observed from their flavor oscillations. We show that carefully prepared beta decay experiments in the laboratory would carry signatures of such a condensation, and thus, it would be possible to either establish or rule out neutrino condensation of cosmological scale in laboratory experiments. 相似文献
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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. 相似文献
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WUNing GermanoResconi ZHENGZhi-Peng XUZhan ZHANGDa-Hua RIJANTu-Nan 《理论物理通讯》2003,40(2):253-256
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. 相似文献
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PENG Huan-Wu 《理论物理通讯》2005,43(1):81-88
Taking Dirac's large number hypothesis as true, we have shown [Commun. Theor. Phys. (Beijing, China) 42 (2004) 703] the inconsistency of applying Einstein's theory of general
relativity with fixed gravitation constant G to cosmology, and
a modified theory for varying G is found, which reduces to Einstein's theory outside the gravitating body for phenomena of short duration in small distances, thereby agrees with all the
crucial tests formerly supporting Einstein's theory. The modified
theory, when applied to the usual homogeneous cosmological model,
gives rise to a variable cosmological tensor term determined by the derivatives of G, in place of the cosmological constant term usually introduced ad hoc. Without any free
parameter the theoretical Hubble's relation obtained from the modified theory seems not in contradiction to observations, as Dr. Wang's preliminary analysis of the recent data indicates
[Commun. Theor. Phys. (Beijing, China) 42 (2004) 703]. As a complement to Commun. Theor. Phys. (Beijing, China) 42 (2004) 703 we shall study in this paper the modification of electromagnetism due to Dirac's large number hypothesis in more detail to show that the approximation of geometric optics still
leads to null geodesics for the path of light, and that the general
relation between the luminosity distance and the proper geometric
distance is still valid in our theory as in Einstein's theory, and
give the equations for homogeneous cosmological model involving
matter plus electromagnetic radiation. Finally we consider the
impact of the modification to quantum mechanics and statistical
mechanics, and arrive at a systematic theory of evolving natural
constants including Planck's ħ as well as Boltzmann's kB by finding out their cosmologically combined counterparts with factors of appropriate powers of G that may remain truly constant to cosmologically long time. 相似文献
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Florian Bauer 《General Relativity and Gravitation》2011,43(6):1733-1757
According to theoretical physics the cosmological constant (CC) is expected to be much larger in magnitude than other energy
densities in the universe, which is in stark contrast to the observed Big Bang evolution. We address this old CC problem not
by introducing an extremely fine-tuned counterterm, but in the context of modified gravity in the Palatini formalism. In our
model the large CC term is filtered out, and it does not prevent a standard cosmological evolution. We discuss the filter
effect in the epochs of radiation and matter domination as well as in the asymptotic de Sitter future. The final expansion
rate can be much lower than inferred from the large CC without using a fine-tuned counterterm. Finally, we show that the CC
filter works also in the Kottler (Schwarzschild-de Sitter) metric describing a black hole environment with a CC compatible
to the future de Sitter cosmos. 相似文献
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Using the linearization of Einstein's equations for weak gravitational fields, a specific model of gravito-magnetofluid is elaborated. The study of wave formation and propagation in such a medium is necessarily connected to the existence of the cosmological constant. 相似文献