Re: heat is a form of energy

[Leigh Palmer <palmer@SFU.CA>]

> Leigh,
> Thanks for your thoughts.  You raise more questions than you answer, but
> that can be a healthy sign.  Rather than going to your specifics, let me
> now impose some of my thoughts on you, and let it rest.

Your thoughts are welcome, Bob, and never an imposition. It is
hard to let it rest, however.

> I model neither energy nor charge as substances; they are calculated,
> mathematical quantities - like scores that one tallies in a game. I have
> exposed the pitfalls of energy reification in the past on this list.

I'm glad you are spreading the message. Perhaps you and I should
put on suits and ring doorbells together. (Sorry, I just had a
couple at the door today. I couldn't resist milking the religious
line.)

How do you calculate charge? I know of no way to do so that does
not depend upon assuming the existence of some "primal charge"
that one must consider substantial. It is for just this reason
that I find charge and energy to be of very different character.

The ultimate way to calculate the charge on a system is to apply
Gauss's law to a bounding surface. That requires one to integrate
the normal component of the electric field over the surface, but
the electric field is defined in terms of a force per unit
charge, and so one must have a charge to start with.

Energy is not calculated in a similar way. One has to fiddle
around and find all the terms which are needed to add up to the
energy of a system. One need not compare the energy to any
standard, either. The law of conservation of energy (the
existence of which is the only reason for defining energy in the
first place) works regardless of what crazy units one uses.

> However, I do find it useful to apply some of the properties of substances
> to mathematical entities, either as metaphors or simply by recognizing a
> commonly accepted widened use of certain words (institutionalized
> metaphors?).  For example, I find it more than a metaphor to apply the
> ability to "flow" to any mathematical quantity which obeys the diffusion
> equation.  It is nigh impossible to express the content of that equation
> without invoking a flow concept.  This equation defines such a concept;
> giving it the label "flow" does not thereby reify the flowing quantity, it
> only gives us a useful visualization (we can only visualize substances,
> not unattached properties).

I agree in part, as I've said before. My objection is to doing so
without qualification of some kind so that the student is made
aware that the analogy is limited. My reason is practical; students
have a difficult time understanding later what entropy is if they
have been raised on substantial energy and then been told, entirely
justifiably, that entropy is, like energy, a function of the state
of the system. Some students graduate with bachelors degrees never
having understood this important concept. One of our bachelors left
SFU not believing in the second law of thermodynamics! (He is now a
professor at an eastern university.)

> "Velocity" is a sister word which certainly was also born as a property of
> substances, but whose metaphorical applications have long since been
> institutionalized in: "phase velocity", "group velocity", "cold front
> velocity" etc.  I do not count these latter phrases as metaphors; they are
> now well defined, useful, technical terms and concepts with meanings of
> their own, and do not of themselves invite unphysical conclusions (no
> caloric spectre here;  but there are pitfalls in eg., "moving
> electrostatic fields", or  - worse -  the velocity of a thing relative to
> an electrostatic field!).

I feel your pain; I share your revulsion. I even found a "moving
magnetic field" flaw in a PRL solid state paper during a seminar by
the author presented while I was a grad student. My professor was
very proud of me. The error involved treating magnetic field lines
as if they were rubber bands, and it got past a referee. The
important thing (from the author's point of view) is that the paper
did get into PRL; it still counts!

There are problems in the professionalism of physicists.

> As you say: "Physics holds no truths about Nature.  The best we can do is
> to construct our best descriptions of Nature . . ."
>
> And the raw materials for this construction are derived from our sensory
> perceptions of corporeal substances.  In our model construction we have
> learned to invent incorporeal, mathematical entities.  We can
> mathematically define the properties of these mathematical entities, but
> in order to speak of them and visualize them we perforce (and always with
> some risk) turn to the properties of corporeal substances. (1)

The first paragraph of your Feynman quotation bears reading and
rereading until its meaning is clear. Description of Nature in
mathematical terms does not always translate easily to vulgar
description. Ultimately we must be capable of listening to the
message in the mathematics; that seems to be Nature's language.
When Einstein said (roughly) "The most incomprehensible thing
about Nature is that it is comprehensible" he implied that his
comprehension was of his sort, and that was mathematical.

Thanks for the quote, Bob.

Leigh