Re: [Phys-l] Arrow of Time Issue

[carmelo@pacific.net.sg]

> On 03/09/2012 02:27 PM, Bennett Sessa wrote:
> > If you have a very messy desk, the entropy of the system is x. If you
> > clean up the desk area, then it would seem that the entropy would
> > decrease,

You may want to read Robert H. Swendsen’s paper on  “How physicists  
disagree on the meaning of entropy.”

Here is an interesting quote:
...no one really knows what entropy really is, so in a debate you will  
always have the advantage.“
John von Neumann’s suggestion to  
Claude Shannon. (Max Jammer’s “Dictionary of the History of Ideas:  
Entropy”)


> I wouldn't have said that.
>
> Messiness (aka disorder) should not be equated with entropy.
>
> Disorder, to the extent that you can define it at all, is a property
> of the microstate.  Entropy is defined as a property of the macrostate.

Nearly all US general chemistry text before 2000, have explained  
entropy using disorderly desk, or messy student room, or shuffled  
cards. It seems that very few US university chemistry textbooks  
published since 2004 still define entropy as disorder. Not sure if  
many physics textbooks have made any changes. Physicists can be more  
stubborn? :-)

To completely remove entropy as measure of disorder may not be the  
best thing. Students should know that there are alternative  
definitions of entropy, and why we prefer new definition of entropy.  
Chemists may prefer entropy as "how much energy is spread out in a  
process."


Best regards,
Alphonsus