Re: [Phys-l] Third Law of Thermodynamics

[John Denker <jsd@av8n.com>]

In a message dated 1/26/2011 4:38:41 P.M. PKeller@holmdelschools.org writes:
> But isn'  t there a problem with talking about "the last bit of heat in a  
> container"?  I thought that there was no such notion as the amount of  heat 
> in a container at ANY time.  How do I talk about the "last  bit"?

On 01/26/2011 05:53 PM, Aburr@aol.com replied:
> > Of course there is a problem. There are lots of them starting with the  
> > term heat (which is why I said heat energy). But you wanted the explanation  on 
> > a HS level.

That's a clever legalism.

However, the problem with legalistic arguments is that even if
you win, it's still just a legalistic argument.  It's not physics.

The statement that set off this subthread was:

> > Heat energy can only be transferred from a container at one temperature to  
> > a container at a lower temperature.
> > Therefore it is impossible to remove the last bit of heat energy from a  
> > container thus making its temperature 0.
> > (This works even with a refrigerator where the lowest temperature is in the 
> >  expansion chamber)

A) Even if you express it in terms of "heat energy" it still gets the 
physics wrong in an important way.  The old-fashioned conventional 
statement of the second law is that "heat" (whatever that means)
cannot flow _of itself_ from a colder body to a hotter body.  The 
"of itself" is in there precisely to create a loophole that allows
refrigerators to exist without violating the second law.  If you
leave out the loophole, the refrigerator stage itself (not whatever
it may be connected to) violates the second law.

You cannot use an invalid version of the second law to "explain"
the third law.

B) Perhaps more importantly, the idea that there is any such thing
as "heat content" or "heat energy content" is not thermodynamics.
It is the theory of /caloric/ ... which has been obsolete since 
1798 (Rumford).  This is my previous argument on steroids; earlier
today I was talking about ideas that have been obsolete since
1898 (Boltzmann) ... but this has been obsolete even longer. Yes, 
there are *some* things that are still well described in terms of 
caloric, such as calorimetry ... but this is not the general case, 
and will never be an acceptable answer to foundational questions
about thermodynamics, such as the question that started this thread.

So ... with or without legalisms, the "heat energy flow" argument 
is at least two bugs removed from the actual physics.

Thirdly, the "heat energy flow" argument is unnecessary.  There
are easier and better ways of answering the original question.

See also next message.