Re: Fields etc

[William Beaty <billb@ESKIMO.COM>]

Hi again Jim!

On Mon, 15 Feb 1999, Jim Green wrote:
> |photons, or as e-fields and/or b-fields.  But just because the "Something"
> |is invisible, or because there are more than one model used to describe
> |it, this does not force us to declare that it is nothing but an abstract
> |concept.
>
> This seems to be offered sort of like a scriptural quote -- just because
> the Great Feynman said something, it must be true.

No, not at all.  My intention was otherwise.
(Also, the above stuff is mine, and Feynman probably would have objected
to parts of it.)

I probably am mis-reading your message, but I imagined that you haven't
encountered this "Poynting EM energy flow" stuff before, and therefor it
might look suspicious.  If instead you're intimately aware of it, but
disagree with the idea, then that's entirely different!

I'm not trying to make argument from authority, instead I'm trying to say
"this is not just some weird Bill Beaty idea, instead it is well known, it
even appears, for example, in Feynman's lectures."


>  Many mis-conceptions
> were started by very great people.  Most notably by Aristotle who said all
> sorts of weird stuff -- some of which we are living with to this day.

And many great discoveries were too.

The idea must stand on its own, we must pick apart the idea and show its
flaws and benefits, without regard to the fame or infamy of its source.
Please don't accept it just because it's from Feynman.  But also, please
don't reject it just because it's more of that Bill Beaty weird stuff.


> Even Feynman joins in this deception in his famous parable of the two
> windows W and Q (I don't remember the details - Feynman aficionados can
> look it up in the Lectures)   He has some stuff -- presumably "energy" --
> being thrown out of one or the other of these windows to describe the First
> Law -- as if energy and heat and work were some sort of substance(s) which
> can move.

Energy is a conserved quantity, therefor in SOME circumstances we can draw
a box around it and calculate the energy inside (or, if we see energy
decrease in one place, it must increase somewhere else.)  Therefor, for
many situations, "conserved quantity" means "substance-like quantity".  As
a mental model, the idea that energy is "stufflike," is useful (but
obviously cannot be applied universally, so we must know the limits if we
ever wish to use this model.  And obviously it carries the possibility for
misconceptions, which must be nipped in the bud at the same time we start
using the models.)

> If I ever have the opportunity to talk personally with Prof Feynman,
> I will pin him down on these points.  I have great faith that he will say
> something like "Oh yes, of course you are right - I just use this imagery
> in my freshman lectures to entertain the kids and clarify things for them.
> I call this bit of subterfuge "mental modeling".  I got the parable from
> one of my old professors  when I was a student."   And I think that he got
> it from one of his professors.

That's what *I* would say: it's all mental modeling.  But EVERYTHING in
physics is mental modeling.  We know the world through our mental models
of it. Without mental models, the world would be a noisy jumble, like
whatever newborn babies must experience.  Obviously all mental models have
limitations, so to be useful, the "model" in our heads must not only have
information about its structure, but also information about its range of
application.  It's that old "tin roof of physics" analogy, where we
attempt to cover all the holes in our understanding by using a large
variety of oddly-shaped patches, yet the result is a fairly solid "roof."
Each "patch" has substance, but it also has a particular "shape" and a
particular way of overlapping with the other "patches."

> But Dick, I will respond, this _doesn't clarify things; it just
> perpetuates bad understanding of physics.  I see why you do it.
> Aristotle so taught his students and they so taught theirs and they so
> taught theirs and ....  But Aristotle didn't know any better; you do (or
> should I say did?) so repent.

We should not care about who tells us to use the models.  Rather ask, ARE
THE MODELS USEFUL?  If there are far better models, then we should use
them instead.  (unless they rightly belong to much higher grade levels!)
:) On the other hand, if we are pursuing "right answers", then we probably
will get into trouble, because the real world is a collection of
interpretations.  If our understanding requires the simultaneous use of
several models, yet we insist on sticking to a single one, then we have a
learning barrier.  In my opinion, insisting on "right answers"  is
destructive to the skills of a physicist, destructive to the employment of
a variety of alternate viewpoints, destructive to the ability to gain
insights by looking at the world through a variety of "lenses" which each
carry their own particular distortions.


Still, I do recognize that, if there is something fundamentally flawed
about this "poynting energy flow" idea, then there is a possible way to
defeat it: just point out the large, fatal flaw.  (Feynman does so.  But
then goes ahead and uses the mental model anyway!  For good reason, in my
opinion.)



> But we should always remind ourselves and our students that we
> just INVENTED the idea of fields.

We also just INVENTED the idea of things like atoms.  I once was befuddled
by the fact that significant numbers of scientists never accepted atoms,
and swore up and down that atoms were just an abstract concept and not
really real.  After participating in the fights about airfoils, etc., it
is no longer a mystery to me why people refuse to accept alternate mental
models, and why these discussions can easily blossom into nasty flamewars.



> RADIO
>
> Electrons in the broadcaster's antenna oscillate and due to the Coulomb
> force cause the electrons in the antenna on my car to oscillate.  I can
> talk about "radio waves", but I know there  is nothing "real" there.  No,
> William, I don't think of radio waves as being real.  In some circles, even
> the electrons are thought not to be "real" in this sense.

OK, now I think I understand.  Yet I still don't know where you draw the
line between real and unreal.  From your above comment, I assume that you
see electrons as real, photons as unreal, e-fields and b-fields as unreal.
How about atoms?  How about electric current?  Or electromagnetic energy?
(When the electric company bills us for the KWH used, are they selling
us a product?  If we pay money for it, does it therefor become "real?")

:)

> Hey, this is just me over here in my little corner.  You all should fell
> free to talk the way you think you otter.

Now if nobody ever disagrees with me, I might never have a chance to lose
all of my embarassing misconceptions which are obvious to everyone but me.


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