# Isn't second law of thermodynamics wrong?

1. Jun 17, 2011

### nouveau_riche

as much i know second law of thermodynamics states that in any closed system the entropy of system always increases(from order to disorder)

can any closed system go from order to disorder without interacting to it's surrounding?
if it can't...then the system will never b closed or the second law of thermodynamics is wrong

2. Jun 17, 2011

### HallsofIvy

I don't understand why you would ask that question- of course it can. Suppose you have gas in a sealed box in which it happens that slightly more than half of the molecules of gas are in the "right" side of the box. Without any interaction with its surroundings, random motion of the molecules will tend to distribute the molecules more evenly- going from "order" to "disorder" and increasing entropy.

3. Jun 17, 2011

### bugatti79

My intuition would tell me that the molecules are going from disorder to order in this particular case because its found its equilibrium....

How comes its the reverse?

bugatti79

4. Jun 17, 2011

### Mathusalem

I think your intuition of Order and Disorder is reverse. The situation described HallsofIvy is said to be ordered. The homogenous distribution of gas which will result is said to be disordered.

It won't stay half-half, because it's a much less probable state than the equidistributed one. Thermodynamics and statistics tell you that the system will inexorably evolve to the most probable state (equiprobable , i.e homogeneously distributed). This most probable state is "disordered".

5. Jun 17, 2011

### nouveau_riche

will the same (as u said) would happen if i reduce the temperature of box surrounding significantly?

6. Jun 17, 2011

### ZapperZ

Staff Emeritus
But then, this is no different than, say, what you would get in a Carnot cycle. While you can reduce the entropy of the system in the box, it is no longer an isolated system (you're now changing the premise of your original question) because there is an external interaction outside because you are asking some "heat reservoir" to absorb the energy from inside the box. You now have to account for the entropy of not just what's in the box, but also what's outside doing the heat absorption.

Zz.

7. Jun 18, 2011

### nouveau_riche

the temp at which the experiment(of box) is performed is not different than case of external interaction plus the inside of box(molecules in it) itself is mixture of many systems,u can approximate the interaction of box with outside world to b negligible but the self enviroment of system takes over the response

8. Jun 18, 2011

### ZapperZ

Staff Emeritus
Huh?

If you are reducing the temperature of the box, you need external source to do that! This is no longer a closed system.

Zz.

9. Jun 18, 2011

### Staff: Mentor

Yes, even a cold gas or a liquid will distribute so that half is on the left and half on the right.

10. Jun 18, 2011

### nouveau_riche

u didn't understand my last msg...the molecules in box itself is an open system...u are making it closed by putting it in box

11. Jun 18, 2011

### ZapperZ

Staff Emeritus
That didn't make it any clearer. Note that you said this:

How do you propose to do that without any external interaction?

Zz.

12. Jun 18, 2011

### Hells

A closed system in thermodynamics is a theoretical construction, there are hardly any completely closed ones in real life, save the universe as a whole. In the case of entropy, it means that if there is a potential difference in energy, it tends to seek a equilibrium and the potential will cease to exist. It's bad in a sense that you can't have change to the system unless you introduce another potential to the system, which will also tends to seek equilibrium and thus you can go on and on. This reduction in potential is called entropy, and by increasing entropy potential is lost.

13. Jun 19, 2011

### nouveau_riche

that means i can't apply 2nd law of thermodynamics in real life....and if i can ,it will just be an approximation

14. Jun 19, 2011

### nouveau_riche

i don't know if this is true but there exist a possibility
"the entropy of the molecules of box (as u may call it) depend upon the non linear characteristics of particles,which is bind to the observer,the box and to the surrounding,so u can't just call entropy to b always increasing in systems....and also 2nd law needs a system which is left onto itself(which i don't think is possible/call it quantum entanglement).....

so the question that needs special attention is"can this law be universal"...for me it ain't

15. Jun 19, 2011

### Staff: Mentor

All of science is an approximation. This is a silly objection. The fact is that it is a good approximation which can be applied in real life in a large number of circumstances.

16. Jun 19, 2011

### ZapperZ

Staff Emeritus
Where do you GET these things? How about providing these sources where you are quoting things from? I do not have time to debunk something that you read off some dubious website.

Besides, what do you consider to be a "universal law"? Give me one example of what you think is a universal law? Newton's laws? Special Relativity? What?

Zz.

17. Jun 19, 2011

### nouveau_riche

firstly i do not quote things after reading ur so called dubious website,that might b ur job
secondly i know that every theory in science has it's domain ....by universal,i was highlighting the universal parameters as they appear...call it gravitational constant,avogadro's number or boltzman or...blah blah..u never changes the value of these constant for different events

regarding that content of this post....i just talked of quantum entanglement that's it

18. Jun 19, 2011

### Staff: Mentor

Please use correct English. SMS messaging shorthand is not acceptable.

You specifically list Boltzman's constant, so then the second law of thermodynamics is universal by that standard.

19. Jun 19, 2011

### ZapperZ

Staff Emeritus
This is nonsense. You somehow cannot differentiate between universal constants versus "principles". And why are we bringing in quantum entanglement?

If you know every "theory in science" has its domain, then what's the issue here? Why is it that you picked the 2nd law to be "wrong", rather than simply allowing it to have its domain of validity? Note your first post. This is what you are arguing, that it is WRONG!

There have been a lot of studies on how thermo's 2nd law works, and how it might be inapplicable in some instances. See this, for example:

http://arxiv.org/PS_cache/cond-mat/pdf/0208/0208291v1.pdf

So such issue is well-known. However, this is done carefully and based on an intimate understanding of what it is. So if you want to talk about what science is, then you must also consider the fact that science can only be challenged based on an intimate knowledge of the exact principle, not based on ignorance of what it is!

Please note that, per what DaleSpam has said, your have explicitly agreed to the PF Rules, which in part, stated this:

Zz.

20. Jun 20, 2011

### nouveau_riche

the link was very uselful,thanks

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