对在光锥上模拟LambdaCDM的不均匀宇宙学模型的年龄检验

发布时间：2018-03-24 03:32

本文选题：宇宙年龄　切入点：LTB宇宙模型　出处：《中国科学技术大学》2011年硕士论文

【摘要】：在通常的演化的宇宙模型里,宇宙年龄指宇宙标度因子为零起到现在时刻的时间间隔。对于有些宇宙学模型,如牛顿宇宙学模型、等级模型、稳恒态模型等,宇宙年龄没有意义。通常,哈勃年龄是宇宙年龄的可靠上限,可以作为宇宙年龄的某种度量。宇宙在膨胀时,它的密度必在减小。逆时间方向往过去追溯,宇宙的密度必在增大。经过有限时间t 0,将追溯到密度为无穷的状态。说明宇宙的膨胀必有一个起点。若把宇宙密度为无穷的时刻规定作时间的零点,则t 0就是今天的宇宙年龄。我们的宇宙有一个有限的年龄。不同的宇宙学模型将会给出不同的宇宙年龄。究竟哪种宇宙模型能更好的描述我们的宇宙,只有通过不同模型给出的结论和宇宙学观测相比较来给出结论。宇宙年龄就是理论与实验比较的一个方面。宇宙年龄无法直接测量,实际测量的是古老天体的年龄。设某天体形成于宇宙年龄为t 1时,设它今天的年龄为τ,则有t_0 = t_1+τ. 这里的“古老”指它形成的很早,以至于t_1τ。对于这样的天体,它的年龄τ就是宇宙年龄t_0的近似。自Rutherford以后,人们常用放射性元素为“钟”,来测量古代遗迹的年龄。考虑到宇宙的年龄约为10Ga左右,因此适合于测龄的放射性元素的寿命应与此在量级上相近。于是被采用的是(233)~T h(寿命τ=20.3Ga); (235)~U (τ=1.02Ga); (238)~U (τ=6.45Ga)等放射性重元素。20世纪80年代以来,人们试用了白矮星的冷却来推断银河系的年龄。在开始形成白矮星时,其内部温度尚很高,因此仍会发光。由于已没有核能源,热辐射将使星体内部逐渐冷却,其辐射光度也相应地逐渐降低。越暗的白矮星内部越冷,年龄也越老。因为冷却过程比核燃烧过程慢,所以很暗的白矮星的年龄几乎就是该恒星的年龄。按这道理,银河系的年龄可以用其中最暗的白矮星的年龄来代表。更为宇宙学家重视的是球状星团年龄的测定。球状星团被认为是银行系中最古老的天体之一。要进一步的用银河系的年龄来推断宇宙的年龄,还需对银河系形成时间做出估计。计算表明银河系的形成时间对宇宙年龄的影响并不大。不同的宇宙学模型会给出不同的宇宙年龄范围。我们比较了现在与观测数据符合得很好的LambdaCDM模型和球对称、不均匀的宇宙学模型的宇宙年龄,两者相差将近2Gyr。
[Abstract]:In the usual evolutionary cosmic model, the cosmic age refers to the interval between the scale factor of the universe from zero to the present moment. For some cosmological models, such as Newton cosmology model, hierarchical model, steady state model and so on, The age of the universe is meaningless. Normally, the Hubble age is a reliable upper limit of the age of the universe, which can be used as a measure of the age of the universe. As the universe expands, its density decreases. The density of the universe will increase. After the finite time t 0, it will be traced back to the state of infinite density. It means that the expansion of the universe must have a starting point. If the density of the universe is defined as the zero point of time when the density of the universe is infinite, So t 0 is the age of the universe today. Our universe has a finite age. Different cosmological models will give different cosmic ages. It is only through the comparison of different models and cosmological observations that the cosmic age is an aspect of theoretical and experimental comparison. The cosmic age can not be measured directly, but the age of an ancient celestial body is actually measured. Let a certain celestial body be formed at a cosmic age of t _ 1 and its present age be 蟿, then there is T _ 0 = t _ 1 蟿. The term "ancient" here means that it was formed so early that t _ 1 蟿. For such an object, its age 蟿 is the approximation of cosmic age _ t _ 0. Since Rutherford, The radioactive element is commonly used as a "clock" to measure the age of ancient relics, considering that the age of the universe is about 10Ga. Therefore, the lifetime of radioactive elements suitable for age measurement should be similar to that of this order of magnitude. Thus, radioactive heavy elements such as T233Th (life 蟿 20.3 Ga1), 235U (蟿 -1.02GaN), 238U (蟿 6.45Ga), and so on, have been used since the 1980s. The cooling of white dwarfs was used to infer the age of the Milky way galaxy. When white dwarfs were formed, the internal temperature was still high, so they would still glow. Because there was no nuclear energy, the heat radiation would cool the stars gradually. The darker the white dwarf is, the colder it gets, the older it gets. Because the cooling process is slower than the nuclear combustion process, the dark white dwarf is almost the age of the star. The age of the Milky way Milky way can be represented by the age of the darkest white dwarf. More important to cosmologists is the determination of the age of globular clusters. Globular clusters are considered one of the oldest objects in the banking system. To extrapolate the age of the universe from the age of the Milky way, It is also necessary to estimate the time of formation of the Milky way Milky way. The calculation shows that the time of formation of the Milky way Milky way does not affect the age of the universe. Different cosmological models give different cosmic age ranges. We compare the cosmological ages of the LambdaCDM model, which is in good agreement with the observed data, and the spherical symmetric, non-uniform cosmological model, and the difference between the two models is nearly 2 Gy r.
【学位授予单位】：中国科学技术大学
【学位级别】：硕士
【学位授予年份】：2011
【分类号】：P159

【共引文献】