## Does Universe contradicts the 2nd law of thermal dynamics?

akltsang

### Does Universe contradicts the 2nd law of thermal dynamics?

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.

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

I read the following story from the web:

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?

akltsang 寫:I read the following story from the web:

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

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.

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.

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

(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。

akltsang

akltsang

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.

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。

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

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.

akltsang 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.

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....

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).