Does Universe contradicts the 2nd law of thermal dynamics?

akltsang
紅巨星
文章: 554
註冊時間: 週六 16 8月, 2003 13:37

Does Universe contradicts the 2nd law of thermal dynamics?

文章 akltsang » 週一 04 11月, 2013 17:05

I read the second law of thermo-dynamics today again and find something very confusing.

The second law said that in any closed system, entropy can only go up (i.e. from ordered to dis-ordered system).

Looking at the Universe as a whole, at the 10^(-n) second after the Big Bang, the university was only full of plasma…. then (after some time) sub-atomic particles were formed, then hydrogen atoms were formed, …. then (after some time) gases, stars, galaxies were formed etc. The Universe was changing from a dis-ordered system (full of free particles) to an ordered system (full of structured things like stars and galaxies). Does it contradict the second law of thermal dynamics?

I know I have assumed that the Universe is closed. What if it is not closed? What’s outside? God?

I am sure there are some physicists here. Can anyone give an explanation to this paradox? I really want to know. Thank you.

頭像
鄧登凳
夸克星
文章: 9497
註冊時間: 週一 03 8月, 2009 17:15
來自: 3rd planet of solar system

文章 鄧登凳 » 週一 04 11月, 2013 17:47

I am not a physicist.

The interpretation of order and disorder cannot be considered by just what we prefer as an orderly manner. The order and disorder in the second law using statistical thermodynamic terms depend on the number of ways energy can be distributed (remembering thermodynamic is about heat energy and not about human feelings).

Also by definition, an equalibrium stage is alway the maximal entropy stage. Although to the general public an equalibrium seem quite "orderly".

akltsang
紅巨星
文章: 554
註冊時間: 週六 16 8月, 2003 13:37

文章 akltsang » 週一 04 11月, 2013 17:56

I read the following story from the web:
有一次,牛頓造了一個太陽系模型,中央是一個鍍金的太陽,四圍各大行星各照各的位置排列整齊,一拉曲柄,各星立即照自己的軌道和諧轉動,非常形象和美妙。一天,哈雷來訪,見到這模型,玩弄了好久,驚嘆叫好,立刻問這是誰造的。牛頓回答說,這個模型沒有人設計和制造的,只不過是偶然有各種材料湊巧碰在一起而形成的。

Newton's explanation is of course impossible, because this violates the 2nd law of thermo-dynamics. However, the Universe seems doing this (from Big Bang to the Universe we see today). Why?

頭像
鄧登凳
夸克星
文章: 9497
註冊時間: 週一 03 8月, 2009 17:15
來自: 3rd planet of solar system

文章 鄧登凳 » 週一 04 11月, 2013 18:24

akltsang 寫:I read the following story from the web:
有一次,牛頓造了一個太陽系模型,中央是一個鍍金的太陽,四圍各大行星各照各的位置排列整齊,一拉曲柄,各星立即照自己的軌道和諧轉動,非常形象和美妙。一天,哈雷來訪,見到這模型,玩弄了好久,驚嘆叫好,立刻問這是誰造的。牛頓回答說,這個模型沒有人設計和制造的,只不過是偶然有各種材料湊巧碰在一起而形成的。

Newton's explanation is of course impossible, because this violates the 2nd law of thermo-dynamics. However, the Universe seems doing this (from Big Bang to the Universe we see today). Why?
What in the explanation of Newton in the story actually violated the second law of thermodynamics??? Please remember all laws of thermodynamics are applicable to only to CLOSED SYSTEMS.

akltsang
紅巨星
文章: 554
註冊時間: 週六 16 8月, 2003 13:37

文章 akltsang » 週一 04 11月, 2013 18:38

Yes, you are perfectly correct. Our solar system can be formed because it was not closed. You cannot imagine that isolating some gases alone, the gas will eventually become a solar system. This violates the second law.

But what about the universe as a whole? If it is closed, then why the gases in it will eventually become stars? That is exactly what I find confusing.

頭像
鄧登凳
夸克星
文章: 9497
註冊時間: 週一 03 8月, 2009 17:15
來自: 3rd planet of solar system

文章 鄧登凳 » 週一 04 11月, 2013 18:50

Consider this closed system:

A simple pendulum in a vacuum box ocsillating left and right with a constant period.

Does this look "orderly"?

This is definitely an equalibrium stage at the end and therefore it is having maximum entropy.

In short, human perception of "order" cannot be used to make claims about the second law of thermodynamics.

頭像
鄧登凳
夸克星
文章: 9497
註冊時間: 週一 03 8月, 2009 17:15
來自: 3rd planet of solar system

文章 鄧登凳 » 週一 04 11月, 2013 19:02

akltsang 寫:Yes, you are perfectly correct. Our solar system can be formed because it was not closed. You cannot imagine that isolating some gases alone, the gas will eventually become a solar system. This violates the second law.

But what about the universe as a whole? If it is closed, then why the gases in it will eventually become stars? That is exactly what I find confusing.
OK. Consider this other closed system:

In a thermally isolated closed container, there is a superstaturated solution (say of copper(II) sulphate). Initially, the solution is just a uniform liquid. Eventually, perfectly geometrically shaped cystals of copper(II) sulphate will form in the container and an equalibrium is reached.

To the human perception: is forming of cystals with perfect geometric shapes representing increase in "order"??

In thermodynamics, the forming of crystals represents increase in entropy and the final equalibrium stage is where maximum entropy is reached. These perfectly shaped crystals actually are in a state of highest disorder of the system.

There is no place for the human sense of order in the discussion of thermodynamics.

akltsang
紅巨星
文章: 554
註冊時間: 週六 16 8月, 2003 13:37

文章 akltsang » 週一 04 11月, 2013 19:25

讓我把思路整理一下:

熱力學第二定律指出,任何封閉系統中,熵只會隨時間增加,不會減少。熵是量度無序的量,所以此定律意思為,任何封閉系統中,物體只會由有序趨向無序。這定律不只在熱力學適用,在其他方面亦適用。例如,一塊石頭最終只會變成一堆沙,你永不會見到一堆沙,自己最終變成一塊石頭。有關此定律的詳情,可看wikipedia.

牛頓的故事表明,一堆雜亂無章的材料 (無序的),不可能自然變成模型 (有序的)。要變成模型,便要人的參與,即原本的材料不是封閉系統。否則這個過程違反第二定律。

同理,我門生存的太陽系,形成前不可能是封閉系統 (即不可能是一堆和其他所有東西完全分離的氣體)自然形成,否則便像牛頓的模型那樣,違反第二定律。

但作為負載所有萬物的宇宙,本身便應該是封閉系統(宇宙的定義就是這樣)。那為什麼在大爆炸之後,本來是一堆混沌的氣體 (無序的),會續步變成星體 (有序的)?

我只想到三個可能:
(a)宇宙不是封閉的。但宇宙之外有什麼?神?
(b)原初宇宙的混沌狀態,比現在的狀態裝更有序 。但我不明白這點的道理。
(c)第二定律對宇宙整體不適用。
最後由 akltsang 於 週一 04 11月, 2013 20:24 編輯,總共編輯了 1 次。

akltsang
紅巨星
文章: 554
註冊時間: 週六 16 8月, 2003 13:37

文章 akltsang » 週一 04 11月, 2013 19:36

鄧Sir的意見,應該是我的第二個可能。這點很難明白。這不是單單個人觀感的分別。事實上,宇宙論的熱寂說,便是說宇宙最終會變成一片熱平衡的氣體,這時熵到達極大值。宇宙最初不是熱平衡的嗎?為甚麼現在變成有溫差了?最後又變回熱平衡?

如果我們把兩杯同溫度的水放在一起,最後一杯自然變成熱,一杯自然變成凍,能源便源源不絕了,事實上這不可能發生。為什麼宇宙卻好像進行了這樣反常的行為?真不明白。
最後由 akltsang 於 週一 04 11月, 2013 21:29 編輯,總共編輯了 1 次。

akltsang
紅巨星
文章: 554
註冊時間: 週六 16 8月, 2003 13:37

文章 akltsang » 週一 04 11月, 2013 21:11

鄧登凳 寫:
OK. Consider this other closed system:

In a thermally isolated closed container, there is a superstaturated solution (say of copper(II) sulphate). Initially, the solution is just a uniform liquid. Eventually, perfectly geometrically shaped cystals of copper(II) sulphate will form in the container and an equalibrium is reached.

To the human perception: is forming of cystals with perfect geometric shapes representing increase in "order"??

In thermodynamics, the forming of crystals represents increase in entropy and the final equalibrium stage is where maximum entropy is reached. These perfectly shaped crystals actually are in a state of highest disorder of the system.

There is no place for the human sense of order in the discussion of thermodynamics.
I am afraid this is not a closed system. There is heat exchange between the container with outside. The crystals are formed because the solution cools down. The entropy inside the container dropped, but the heat is dissipated to outside and increased the entropy outside. The over entropy increased.

頭像
鄧登凳
夸克星
文章: 9497
註冊時間: 週一 03 8月, 2009 17:15
來自: 3rd planet of solar system

文章 鄧登凳 » 週一 04 11月, 2013 21:43

你要小心考慮我提出密閉和熱絕系統中的超飽和溶液問題。

超飽和硫酸銅(II)溶液, 是個顏色、濃度、溫度都平均的溶液, 但放在不容許物質和熱量有任何交換的密閉系統, 經以時日一定會結出形狀十分工整的藍色結晶。屢試不爽的! 絶對是密閉系統內的天然事件而不需任何"外力"的。

一般人一定認為有工整的結晶體出現, 由於形狀是十分有秩序的, 因此系統是增加了"有序性"。這個說法問題不大, 但當你一將一般人觀感上的"有秩序"和熱動力學第二定律等同起來, 就是嚴重的問題。

熱動力學的統計熱力學解說, "有序"和"無序"只關係一件事情, 就是能量有多少可以分佈的方式數量(multiplity of energy distribution, 請細閱: http://hyperphysics.phy-astr.gsu.edu/hb ... lteng.html)。以上面的例來說, 硫酸銅(II)結晶是個放熱反應, 在熱絕系統中結晶時, 整體系統的溫度會增加, 那多了熱能去作分佈, 可以分佈的方式一定更多, 而增加一個物相(phase), 也一定增加能量可分佈的方式數量。所以結出有工整形狀的結晶, 是會增加系統的熵(能量分佈無序程度) 。

重點是, 不能用觀感上的有序來討論熱動力學, 而要用能量可能分佈的方式數量來考慮。不能說平均的超飽和溶液生出的工整的結晶, 就是一個違反第二定律的無中生有過程。

順便一說:
1. 現時的理解, 建基於電腦模擬的宇宙初期, 單是靠我們所知的「可見物質」不會自動形成物質的聚集而產生星系及其中的恆星, 當中必需有一些有重力但和電磁波沒有反應的物質存在才可以, 這些一般稱為暗物質(見: http://chronicle.uchicago.edu/060713/darkmatter.shtml)。由於我們對暗物質的認識近乎零, 所以怎樣將暗物質放入熱力學的計算中, 是沒法確定的。
2. 將一個模型合併起來或分散放置, 不會改變這個模型物質的能量可分佈方式數量, 即不會引來熵的變化。由於沒有熵的變化, 第二定律完全不適用。
3. 有沒有一位造物主, 是另一層面的問題, 和熱動力學第二定義沒有關係。
最後由 鄧登凳 於 週一 04 11月, 2013 22:04 編輯,總共編輯了 1 次。

大黃傻貓GARFIELD
中子星
文章: 1543
註冊時間: 週日 11 9月, 2005 01:34

Re: Does Universe contradicts the 2nd law of thermal dynamic

文章 大黃傻貓GARFIELD » 週一 04 11月, 2013 21:48

akltsang 寫:I read the second law of thermo-dynamics today again and find something very confusing.

The second law said that in any closed system, entropy can only go up (i.e. from ordered to dis-ordered system).

Looking at the Universe as a whole, at the 10^(-n) second after the Big Bang, the university was only full of plasma…. then (after some time) sub-atomic particles were formed, then hydrogen atoms were formed, …. then (after some time) gases, stars, galaxies were formed etc. The Universe was changing from a dis-ordered system (full of free particles) to an ordered system (full of structured things like stars and galaxies). Does it contradict the second law of thermal dynamics?

I know I have assumed that the Universe is closed. What if it is not closed? What’s outside? God?

I am sure there are some physicists here. Can anyone give an explanation to this paradox? I really want to know. Thank you.
The forming of hydrogen atoms/matters/stars and galaxies does not contradict the second law of thermal dynamics, because in all cases, there is no net energy input to this universe from "outside" at all.
Theoretical physicists as well as astrophysicists have calculated the net amount of energy in the universe is ZERO.

All it happens are energy being converted to matter, as predicted by Einstein's equation E=mc^2

At the Big Bang, the energy so called, as physicists today understand, is a quantum fluctuation. There is a plus and a minus to make the net energy zero.

The fluctuation caused the raging of energy at the Big Bang, and as the universe expands, it cooled, allowing the energy to condense to matter.

頭像
鄧登凳
夸克星
文章: 9497
註冊時間: 週一 03 8月, 2009 17:15
來自: 3rd planet of solar system

文章 鄧登凳 » 週一 04 11月, 2013 21:49

akltsang 寫:
鄧登凳 寫:
OK. Consider this other closed system:

In a thermally isolated closed container, there is a superstaturated solution (say of copper(II) sulphate). Initially, the solution is just a uniform liquid. Eventually, perfectly geometrically shaped cystals of copper(II) sulphate will form in the container and an equalibrium is reached.

To the human perception: is forming of cystals with perfect geometric shapes representing increase in "order"??

In thermodynamics, the forming of crystals represents increase in entropy and the final equalibrium stage is where maximum entropy is reached. These perfectly shaped crystals actually are in a state of highest disorder of the system.

There is no place for the human sense of order in the discussion of thermodynamics.
I am afraid this is not a closed system. There is heat exchange between the container with outside. The crystals are formed because the solution cools down. The entropy inside the container dropped, but the heat is dissipated to outside and increased the entropy outside. The over entropy increased.
I have indicated that it is thermally isolated. I can assure you that you get crystals putting the solution in a vacuum flask with no heat gain or lost. In reality, the solution heats up when ionic crystals are formed. See discussion above.

PS. Equalibrium is reached when the solubility increase that comes with the increasing temperature makes the solution a saturated one instead of a supersaturated one.
最後由 鄧登凳 於 週一 04 11月, 2013 22:06 編輯,總共編輯了 1 次。

大黃傻貓GARFIELD
中子星
文章: 1543
註冊時間: 週日 11 9月, 2005 01:34

文章 大黃傻貓GARFIELD » 週一 04 11月, 2013 21:53

On the Second Law of thermal dynamics side, to put it in energy terms, is that, there is no turning back when a form of energy is converted to another or being expended from some reactions.

The energy of stars are from fusion of hydrogen atoms, but you cannot turn from that fusion back to its original state, so as a result, the universe will gradually exhaust all its "fuel".

Of course how the universe will end is a debate among astrophysicists, and many will say we will end up in a Great Rip....

頭像
鄧登凳
夸克星
文章: 9497
註冊時間: 週一 03 8月, 2009 17:15
來自: 3rd planet of solar system

文章 鄧登凳 » 週一 04 11月, 2013 22:00

Don't even require quantum theory to predict temperature fluctuation.

If all particles in a system have energy level exactly the same with each other, there is one and only one way to distribute the energy. While particles all have different energy levels, there are many many more ways to distribute energy. So in statistical thermodynamics, it is predicted that particles in a "system" will have different energy levels with one and other. This varied temperature represents increase in entropy. The distribution of energy/temperature should follow the Maxwell-Boltzmann distribution (see http://ibchem.com/IB/ibnotes/full/sta_h ... tzmann.htm).

回覆文章

回到「天文物理 Astrophysics」

誰在線上

正在瀏覽這個版面的使用者:沒有註冊會員 和 1 位訪客