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Re: energy is real



At 08:57 AM 3/16/00 -0800, Leigh Palmer wrote:
At 9:58 PM -0800 3/15/00, John Denker wrote, inter alia:

>1) Energy is real.

Would you care to defend this position or is it a pronouncement
*ex cathedra*?


That position can be defended in multiple ways.

First and foremost, usefulness: Some people find energy to be a useful
concept. If it's not useful to you, that's your problem. Please don't
inflict your problems on other people.

As a general rule, you should leave X alone unless
a) you can show that X is absolutely harmful, and/or
b) you can replace X with something relatively better.

In this case X is the notion of energy, and the local conservation thereof.
a) Maybe you can show that the notion is wrong, perhaps by demonstrating
a formal contradiction or inconsistency in the theory, or by showing that
it makes a prediction that is inconsistent with experiment.
b) Maybe you have a better way to do the calculations that other people
do using the energy notion.

In either case, the burden is on _you_ to recruit believers by
demonstrating that you have a more useful way of doing things. Just saying
no no no everybody else is wrong (without offering anything better) is
unlikely to bring many recruits.

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

Another argument: My dictionary defines "real" mainly as the opposite of
fictional.

Ghosts are fictional; energy is real. If I write a fiction book about
ghosts, I can say pretty much anything I please. For instance, I might say
that they can disappear from inside a box and reappear outside the box
without necessarily passing through the walls of the box. In contrast, if
I write a physics book about energy, I am very highly constrained as to
what I can say. I am constrained by reality. In particular, I cannot say
that energy passes from inside the box to outside without passing through
the walls of the box.

In this sense, energy and other abstractions have a more permanent reality
than, say, hydrogen atoms do. If I have a box that is impermeable to
hydrogen, I can turn hydrogen atoms into something else (e.g. neutrons)
that silently escape from the box; the net result is that hydrogen atoms
disappear from the interior without ever passing (as such) through the walls.

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

To return to the usefulness argument: Usefulness applies to doing
calculations and to communicating. The notion of energy is useful for both.

A couple of days ago I was teaching my student Jay how to land an
airplane. We were on final approach. He was somewhat too high (potential
energy) and somewhat too fast (kinetic energy). It was obvious to me that
he had an energy problem. We discussed this. It was a question of when
(not if) he would break off the approach and go around for another
try. The difference between a satisfactory approach and an unsatisfactory
approach was energy. For all practical purposes, energy was the *only*
difference. And until somebody comes along with a better word, I will
continue to call it energy when doing calculations and when communicating
with my students. Jay certainly knew what I meant by energy. Energy was
pretty darn real to him. He tried everything he could think of: closing
the throttle, extending full flaps, putting the thing into a radical slip,
but he just couldn't get rid of enough energy.

You should try it some time: try to get rid of some unwanted energy in a
hurry. If you think energy is fictional, if you think you can make energy
disappear just by wishing, then your wishes are much more powerful than
mine. Please tell us all how you do it!