本文選題：宇宙年齡　切入點：LTB宇宙模型　出處：《中國科學技術大學》2011年碩士論文

【摘要】：在通常的演化的宇宙模型里,宇宙年齡指宇宙標度因子為零起到現(xiàn)在時刻的時間間隔。對于有些宇宙學模型,如牛頓宇宙學模型、等級模型、穩(wěn)恒態(tài)模型等,宇宙年齡沒有意義。通常,哈勃年齡是宇宙年齡的可靠上限,可以作為宇宙年齡的某種度量。宇宙在膨脹時,它的密度必在減小。逆時間方向往過去追溯,宇宙的密度必在增大。經過有限時間t 0,將追溯到密度為無窮的狀態(tài)。說明宇宙的膨脹必有一個起點。若把宇宙密度為無窮的時刻規(guī)定作時間的零點,則t 0就是今天的宇宙年齡。我們的宇宙有一個有限的年齡。不同的宇宙學模型將會給出不同的宇宙年齡。究竟哪種宇宙模型能更好的描述我們的宇宙,只有通過不同模型給出的結論和宇宙學觀測相比較來給出結論。宇宙年齡就是理論與實驗比較的一個方面。 宇宙年齡無法直接測量,實際測量的是古老天體的年齡。設某天體形成于宇宙年齡為t 1時,設它今天的年齡為τ,則有t_0 = t_1+τ. 這里的“古老”指它形成的很早,以至于t_1τ。對于這樣的天體,它的年齡τ就是宇宙年齡t_0的近似。自Rutherford以后,人們常用放射性元素為“鐘”,來測量古代遺跡的年齡�？紤]到宇宙的年齡約為10Ga左右,因此適合于測齡的放射性元素的壽命應與此在量級上相近。于是被采用的是(233)~T h(壽命τ=20.3Ga); (235)~U (τ=1.02Ga); (238)~U (τ=6.45Ga)等放射性重元素。20世紀80年代以來,人們試用了白矮星的冷卻來推斷銀河系的年齡。在開始形成白矮星時,其內部溫度尚很高,因此仍會發(fā)光。由于已沒有核能源,熱輻射將使星體內部逐漸冷卻,其輻射光度也相應地逐漸降低。越暗的白矮星內部越冷,年齡也越老。因為冷卻過程比核燃燒過程慢,所以很暗的白矮星的年齡幾乎就是該恒星的年齡。按這道理,銀河系的年齡可以用其中最暗的白矮星的年齡來代表。更為宇宙學家重視的是球狀星團年齡的測定。球狀星團被認為是銀行系中最古老的天體之一。要進一步的用銀河系的年齡來推斷宇宙的年齡,還需對銀河系形成時間做出估計。計算表明銀河系的形成時間對宇宙年齡的影響并不大。 不同的宇宙學模型會給出不同的宇宙年齡范圍。我們比較了現(xiàn)在與觀測數(shù)據(jù)符合得很好的LambdaCDM模型和球對稱、不均勻的宇宙學模型的宇宙年齡,兩者相差將近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.
【學位授予單位】：中國科學技術大學
【學位級別】：碩士
【學位授予年份】：2011
【分類號】：P159

【共引文獻】

相關期刊論文 前1條

1 趙偉;李新洲;;關于LTB宇宙模型中的Friedamann方程[J];上海師范大學學報(自然科學版);2010年05期

相關碩士學位論文 前2條

1 趙偉;LTB宇宙及其相關問題研究[D];上海師范大學;2011年

2 周康;高維Lovelock引力下天體的平衡與坍縮[D];西北大學;2012年

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本文編號：1656547