Re: energy is only an attribute

[William Beaty <billb@ESKIMO.COM>]

On Thu, 3 Feb 2000, Chuck Britton wrote:

> and I MIGHT buy into it when the grad schools QUIT TEACHING THE
> POYNTING VECTOR!!!
>
> (or else come up a suitable set of waffle words so that we poor
> unsuspecting students are no longer tempted to think in terms of
> energy transport.)

The same topic arises again and again.  This is about "religious
positions" and systems of belief, so there's no way to win the debate.

A counterargument:

  Throw me a well-discharged capacitor.  I then "charge" it from my power
  supply.  I throw it back to you.  You use it to briefly heat a resistor.
  You throw it back to me, and we repeat the process.  As long as the
  capacitor keeps circulating, you can keep your resistor warm.

  The capacitor goes back and forth between us.  The amount of charges
  within the capacitor never varies, so there is no net flow of charge,
  and there is no net flow of capacitors from me to you.

  However, I'm transporting something to you.  I'm transporting "ability
  to do work."  I'm also transporting matter, since a charged capacitor
  weighs a tiny bit more than a neutral capacitor by E=mc^2.  What flows
  from me to you?  Matter?  Energy?  E-field?  SOMETHING flows, and this
  something is substance-like, it is a conserved quantity.  If I draw a
  surface around you, then the only way that this "something" can get to
  you is if it penetrates the surface.  I decide give this "something"
  the name "energy," and when it moves from me to you, I call it
  "energy flow."

I think an earlier response to the above was that energy isn't always
localizable as in the capacitor example, therefor 'energy' is more like a
property than like a substance.  (Or did I misremember?)

I could next argue that matter doesn't exist either, it isn't always
localizable, therefore it's just a property of something else.  Or I could
argue that NOTHING exists but properties, since we deal entirely with
perceptions and mental constructs and can never make contact with the
essence of the world outside our minds.  If everything is properties, then
conserved properties like charge, mass, and energy are more real than
other properties.

Also: when a capacitor drives a resistor, the Poynting-vector conceptually
indicates that the energy comes from the space around the resistor.  It
also shows that the energy travels parallel to the wires in the space
surrounding them, and then dives into the resistor when it arrives there.
It also shows that the energy comes from between the plates of the
capacitor as it discharges; it spews out of the capacitor and into the
space surrounding the capacitor.  As with flowing substances, the "energy"
doesn't magically arise and vanish, instead it originates in one spot,
moves through space, and then ends up in another spot.  Very substance-
like, no?

What's the big problem?  Radio-stuff and light-stuff both do something
similar. Electric circuits are simply the DC case, but even this isn't
true.  Just replace your battery with a 10MHz oscillator, and the
flashlight bulb still lights up.  Or make your flashlight circuit a few
light-seconds across and even a battery will generate bouncing pulses of
EM-stuff.

In my opinion, the fact that this all hangs together conceptually is the
important thing.  The pieces of the puzzle mesh together.  If one of the
unifying concepts (energy is substance-like) is declared taboo, then that
seems destructive rather than beneficial.  It interferes with profound
understandings and "aha"  experiences.


That said, I do agree that "energy is substance-like" and "energy can
flow" are just mental tools.  The same is true of concepts like "cup" and
"desk" and "Bill Beaty."  They are just mental aides.  If I throw a cup to
you, did "a flow of cup" take place?  NO!  "Cup" is not a conserved
quantity, and if I first ground the cup into powder before tossing it,
then no cups flowed.

Perhaps "flow of mass" and "flow of energy" are MORE REAL than the motions
of everyday objects?


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