Re: [Phys-l] States of matter?

[John Denker <jsd@av8n.com>]

On 10/13/2011 04:33 AM, Peter Schoch wrote:
> I find myself in the middle of a heated debate by our Chemists.
> Several of them gives the states of matter as:  solid liquid, gas,
> plasma.  The opposing group vehemently objects to the inclusion of
> plasma as a state of matter, as they claim it is just a special case
> of gases.
>
> Why they think that I, as a physicist, would be a great arbiter of
> this is a mystery to me.  After a bit of research I am leaning toward
> the traditional "solid, liquid, gas" argument; however, before
> sticking my head in the lion's mouth I thought I would solicit
> opinions here.

I think you should conduct a vote.  Do it the MIT way,
where people vote with money.  That is, set up two boxes
outside your door, one labeled "solid liquid gas" and the
other labeled "solid liquid gas plasma".  Then people can
put money into one box or the other, according to which
outcome they favor ... and in proportion to how much they
care.

At the end of the week you count the money and announce
the result.

You keep the money.

If somebody notices that this looks like an arbitrary answer
to a trivial question, explain that it looks that way because
it *is* an arbitrary answer to a trivial question.

Solids exist.
Liquids exist.
Gases exist.
Plasmas exist, and are easily distinguished from solids,
  liquids, and gases.
There is such a thing as a "photon gas" that is easily
  distinguished from any of the above.
Superfluids exist, and are separated from the classical
  fluid by a phase transition as sharp as any transition
  from liquid to gas (actually *more* reliably sharp).
Ferromagnetism exists, and is separated from the non-fm
  state by a first-order phase transition.
Liquid crystals are readily distinguishable from ordinary
  liquids and from ordinary crystals.

Need I go on?

Whether these things are called states or phases or both
or neither is purely a question of terminology.  As such
it is both trivial and arbitrary.

As the ancient proverb says, academic disputes are particularly
vicious because there is so little at stake.

As has been said many times before:  Ideas are primary.
Terminology is tertiary.  Terminology is important only
insofar as it helps us formulate and communicate the ideas.

Your colleagues need to figure out what idea(s) they are
trying to express.  Possibly some of them are trying to
express one idea and some of them another.  If they think
that an arbitrary decision about the terminology is going
to help with this, they are grievously mistaken.

As another way of making the same point:  There is a proverb 
that says, if you can't tell the difference, it doesn't matter.

So ask them:  Suppose you give answer "A".  What are they
going to do differently?  Suppose you give answer "B".
What are they going to do differently?

===================

There is one situation where there could be a nontrivial
positive outcome.

Sometimes there are two (or more!) ideas hiding under a
single piece of terminology.
 -- In mechanics, there are two reasonable definitions of
  "acceleration"
 -- In thermodynamics, there are at two definitions of
  "adiabatic" and at least four technical definitions of
  "heat" in common use, not to mention innumerable rare,
  non-technical and/or metaphorical meanings.
 -- et cetera

In such a case, an arbitrary decision about "the" definition
is absolutely the wrong thing to do.  You need to /split/
the terminology.  You need to come up with two (or more!)
terms, so that the terminology begins to express the actual
ideas.  For example:
  -- acceleration --> scalar acceleration and/or vector acceleration
  -- adiabatic --> isentropic and/or thermally isolated
  -- heat --> energy and/or entropy
  -- et cetera.

So, again:  Ask each of them what /idea/ they are trying
to express.  Then see if you can find -- or coin -- some
terminology to express the idea.  Do not limit the search
to single words;  adjectives exist for a reason.

OTOH be prepared for the possibility that they have no 
idea what they are arguing about, and are just arguing
for the sake of arguing.