＂奥尔贝葛的疑题＂或 ＂Olbers' Paradox"

koren

好的。我有一个问题： 谁明白什么是 ＂奥尔贝葛的疑题＂或 ＂Olbers' Paradox"

Axiom #1 物理定律在所有任何时间和地点都是一样的。
Axiom #2 这个宇宙是扁平的，或 "Euclidean"
Axiom #3 我们人类生存在在宇宙任何一个角落都是一样的地方。（We live in a typical part of universe.) (我们的存在并非特别的）
Axiom #4 这个宇宙基本上是静止的。

Olbers，１８００发表了这个疑问， 为何我们在白天可以看到／察觉光的存在，（就是我们看到光,走路时就不会因为没有光而跌到。 ）而，晚上就看不到光呢？
除了从无限远的宇宙其它星系所传来的光。星光也是光，光在宇宙是3X10e8 的速度行动，不间断。既然是光，为何不象白天的光（太阳光）一样光，使夜晚和白天一样光？

当时的科学家都认为，天空应该是无限明亮的。（就是没有白天／黑夜）如果他们基于宇宙是无限整体性的学说。

我看了一阵子，都找不到这疑问的破绽。 我们知道这疑问是有地方是错误的。可是如何指正？
而且作者的解说有点难以明白。 请各位高手解开我心结！

你的问题极难，我只好抛砖引玉了。

先在的物理学家或天文学家门较相信宇宙由一个大爆炸(big Bang)而产生。所以宇宙有年龄并向四处扩张而不是Olber所说的那样（何时间和地点都是一样的，宇宙基本上是静止的。。。。）。

因此，不是每一个衡星的光都能到达地球（因为太遥远了），所以地球有分日夜。

欢迎纠正。

[ Last edited by 埃历恩 on 1-3-2005 at 11:28 PM ]

koren

稍微补充。
Axiom#4 乃因为牛顿重力定律，各自行星与其他星体在重力的牵引下，在进行复杂无止竟的互相吸引，离开等运动。可是，最终，重力的吸引会把宇宙所有星体运动＂拉＂平时，那么，就是宇宙停止不动了。

有听说过 ＂Zero Point Energy" 吗？
请看原文：
In a quantum mechanical system such as the particle in a box or the quantum harmonic oscillator, the lowest possible energy is called the zero-point energy. According to classical physics, the kinetic energy of a particle in a box or the kinetic energy of the harmonic oscillator could be zero - namely if the velocity were zero. But quantum mechanics with its uncertainty principle implies that because the uncertainty of the exactly vanishing velocity is zero, the uncertainty of the position must be infinite. This either violates the condition that the particle remains in the box, or it brings a new potential energy in the case of the harmonic oscillator. The minimal velocity allowed by quantum mechanics is therefore not strictly zero, and therefore the minimal energy is not zero either.

koren

Olbers' paradox, described by the German astronomer Heinrich Wilhelm Olbers in 1823 and earlier by Johannes Kepler in 1610 and Halley and Cheseaux in the 18th century, is the paradoxical statement that in a static infinite universe the night sky should be bright. This is sometimes also known as the "dark night sky paradox".
Contents [showhide]
1 Assumptions
2 Explanations
3 Resolutions
4 References
[edit]

Assumptions

If the universe is assumed to be infinite, containing an infinite number of uniformly distributed luminous stars, then every line of sight should terminate eventually on the surface of a star. The brightness of a surface is independent of its distance, so every point in the sky should be as bright as the surface of a star.

It should be noted that for stars to appear "uniformly distributed" in space they must also be uniformly distributed in time, because the further away one looks, the older what one sees is. On an infinite scale, this means the universe must be infinitely old with no dramatic changes in the nature of stars in that time.

Kepler saw this as an argument for a finite universe, or at least for a finite number of stars, but the argument is not convincing as will be shown below.
[edit]

Explanations

One explanation attempt is that the universe is not transparent, and the light from distant stars is blocked by intermediate dark stars or absorbed by dust or gas, so that there is a bound on the distance from which light can reach the observer. However, this reasoning does not resolve the paradox. According to the first law of thermodynamics, energy must be conserved, so the intermediate matter would heat up and soon reradiate the energy (possibly at different wavelengths). This would again result in uniform radiation from all directions, which is not observed.

The explanation of the paradox to gain the most scientific consenus points to the finite speed at which light travels through space. Given its finite speed, the light from the most distant star cannot have travelled a further distance, measured in light years, than the star itself is old. This explanation was first offered by poet and writer Edgar Allan Poe, who observed:

    "Were the succession of stars endless, then the background of the sky would present us an uniform luminosity, like that displayed by the Galaxy -–since there could be absolutely no point, in all that background, at which would not exist a star. The only mode, therefore, in which, under such a state of affairs, we could comprehend the voids which our telescopes find in innumerable directions, would be by supposing the distance of the invisible background so immense that no ray from it has yet been able to reach us at all."[1] (http://eserver.org/books/poe/eureka.html)

Holding the universe to be approximately 15 billion years old, the furthest expanse that light could have possibly travelled since its creation is an equal number of light years. Thus, even if every infinite trajectory into space from the earth eventually passes through a star in the furthest regions of the universe, the light of all such stars beyond the maximum distance in which light has travelled since the origin of the universe will remain beyond visibility from earth.
[edit]

Resolutions

The paradox is resolvable in a variety of ways.

If the universe has existed for only a finite amount of time, as the prevalent Big Bang theory holds, then only the light of finitely many stars has had a chance to reach us yet, and the paradox breaks down. Alternatively, if the universe is expanding and distant stars are receding from us (also a claim of the Big Bang theory), then their light is redshifted which diminishes their brightness, again resolving the paradox. Either effect alone would resolve the paradox, but according to the Big Bang theory, both are working together; the finiteness of time is the more important effect. Some see the darkness of the night sky to be evidence in support of the Big Bang theory.

Even without the Big Bang theory and its redshift evidence, we may establish the finite age of the universe (in its present form) by a mathematical evaluation of hydrogen. Assume that the amount of mass in stars divided by the total amount of mass in the universe is nonzero. After some length of time, any given star will convert too much hydrogen into helium (or heavier elements) to continue nuclear fusion. From this we conclude that in unit time, the amount of hydrogen converted into helium by a given star divided by the star's mass is nonzero. Combining this with the earlier statement, we conclude that the amount of hydrogen converted into helium by stars as a whole divided by the mass of the universe is nonzero. There is no known process that can return heavier elements to hydrogen in the necessary quantities, and any would probably violate the second law of thermodynamics. Therefore, the amount of time needed for stars to convert all of the hydrogen in the universe into helium is finite, and it will never change back. After this, only heavier-element-burning stars will exist (and these will die when they hit iron, an event known as the heat death of the universe). This hasn't happened yet, so either the universe is of finite age, it has undergone major changes in its history, or there exists some highly exotic process (for which no direct evidence exists) that produces hydrogen to keep it going.

A different resolution, which does not rely on the Big Bang theory, was offered by Benoit Mandelbrot. It holds that the stars in the universe may not be uniformly distributed, but rather fractally like a Cantor dust, thus accounting for large dark areas. It is currently not known whether this is true or not, although recent satellite studies have found the cosmic microwave background radiation is isotropic to 1 part in 10000.
[edit]

References

    * Relativity FAQ about Olbers' paradox (http://math.ucr.edu/home/baez/physics/Relativity/GR/olbers.html)
    * Astronomy FAQ about Olbers' paradox (http://www.faqs.org/faqs/astronomy/faq/part9/section-17.html)
    * Cosmology FAQ about Olbers' paradox (http://supernova.lbl.gov/~evlinder/umass/faqm.html#olber)
    * Paul Wesson, "Olbers' paradox and the spectral intensity of the extragalactic background light", The Astrophysical Journal 367, pp. 399-406 (1991).
    * Edward Harrison, Darkness at Night: A Riddle of the Universe, Harvard University Press, 1987
    * Scott, Douglas, and Martin White, "The Cosmic Microwave Background (http://www.astro.ubc.ca/people/scott/cmb_intro.html)".

转贴：
资料来自wikipedia.
然后，我在看的书叫 ＂Revserve Time Travel" by Barry Chapman.
是关于 空间－时间 的联系性和时间与超越光速宇宙远程旅行的可能性和研讨。

非常有趣， 是一本较深入物理／相对论／时空的入门书籍。
能够找到的人就请你一看咯！

isbn 0-304-34524-5

Asurahyde

很好的一篇文章。我又上了一課了。

加分鼓勵﹗

ah@boy

我想试下回答那个地球分日夜的问题...
我猜是宇宙中的黑洞把那些光都吸走了,所以遥远的光不会射到地球....
请批评..谢谢

koren

答案错误， 如果光给吸走的话，那么地球危险了。

有的光是在太遥远的地方，以至到现在那里的光还没能传到这里。
不过，以上的也不算是答案。

fritlizt

哈哈， 我有个比较笨的想法 。
远处的光在来到地球之前，会经过很多星体，加上那些星体有些本身有空气。 所以那些远处的光到达地球时，光的强度可能会或等于零了。
*这边我假设会发光的星体比不会发光的星体少。

ah@boy

其实这些光根本就有射到地球来,这些光就是我们晚上看到的星光咯...哈哈..

ah@boy

我的说法对不对呢??
,,,怎么没人来了....??

koren

没有空也，所以没来看。

迟一点，把书本渗透后在来。