Re: Zero Points?

On Fri, 04 Sep 2009 17:05:15 -0700, Hatunen <hatunen@xxxxxxx> wrote:

On Fri, 4 Sep 2009 21:28:25 +0200, nospam@xxxxxxxxxxxxxxxx (J. J.
Lodder) wrote:

Murray Arnow <arnow@xxxxxxxxx> wrote:

J. J. Lodder wrote:
Murray Arnow wrote:

J. J. Lodder wrote:
Murray Arnow wrote:

Lars Eighner wrote:

Temperature does, of course, have a zero that means zero, but that is
not the zero of several temperature scales. Kelvin uses the zero that
is zero. Celsius and Fahrenheit do not. Their zeros are as arbitrary
as the zero of longitude.


It's when you are absolutely sure, you should question the most. If the
Kelvin zero is zero, then there would be no negative energies. The fact
is all scales are arbitrary. It is convenient in Statistical Mechanics
to set a zero-point temperature, but it isn't necessary.

It's necessary.
Thermodynamics defines ratios of (absolute) temperatures only,


I that true?

Yes.

Classical thermodynamics, in my recollection, says that an
empirical temperature exists and is defined through the equation of
state, F(P,V)=T. This doesn't demand a zero. I guess you could invoke
the Third Law to demand a zero temperature, but, in general, the
existence of a zero-point temperature isn't necessary to do
thermodynamics.

Classical thermodynamics doesn't depend on any equation of state
or empirical temperature scale. (any will do)
The concept of thermodynamic (aka absolute) temperature
is derived from the first and second law.
(by incredibly clever reasoning)
However, termodynamics defines only ratios of temperatures,
so one particular point has to be chosen to fix the unit.

In other words, temperature is a multiplicative quantity,
not an additive one. So a zero is inevitably implied,

Jan

I have a few points of contention with the above, Jan. I won't go into a
rebuttal here, because it will only confirm the Fourth Law of
Thermodynamics: conversations on about thermodynamics, in AUE,
inevitably end flame wars.

Really? Thermodynamics is one of the dullest
and least controversial subjects in physics.
The only way to get into heated discussions about it
is to invite some IDiots.

Thermodynamics frequently becomes disputatious because there are
many people who don't believe that one must, inevitably, always
lose energy.

I believe it, but I get more and more tired of hearing about it as
time goes on. I think I'll take a nap now.
--

Regards,

Chuck Riggs,
who speaks AmE, lives near Dublin, Ireland
and usually spells in BrE
.

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