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Re: [Phys-L] explaining stuff the right way, or not

I wholeheartedly agree to everything in this post. In particular, I was taken by the "There is always a temptation to tell students that the subject is more complicated than it really is. This is an occupational hazard. We must recognize it as such and constantly guard against it."

I have a friend teaching stats at Stanford. When he makes up a test, he passes it to a few colleagues for a review. He ruthlessly deletes items that any of them comments on as "nice," or "neat," or similar.


On 2/20/2013 11:55 AM, John Denker wrote:
On 02/19/2013 05:56 PM, David Marx wrote:

It takes
a while to explain, but quantum mechanics makes sense. You have to tailor you explanations for young
students, but you should not imply its nonsense. It should not be presented as a mystery of faith or a
Koan as a previous commenter suggested. I can't think of a better way to put people off from science
than to put on a little play saying that quantum is some kind of Lovecraftian monster that will cause you
to flail around like a crazy person once it is revealed to you."

I agree with the sentiment there, although I might take a different
path to arrive at the same conclusion.

I would say that *if* you look closely enough at QM (or anything
else) you can find some weird things. However, it would be grossly
irresponsible to emphasize /or even mention/ such things in an
introductory class.

In particular, making a big fuss about wave/particle duality is
just bad pedagogy. Students nowadays don't know enough about
classical waves *or* classical particles to care about the
distinction. The best strategy is to tell them that in the
real world there is no distinction between waves and particles;
there is only "stuff". Depending on how you design the experiment,
sometimes "stuff" looks like a wave and sometimes it looks like a
particle. This is a simplification, not a complexity, because
there is only one kind of "stuff". You don't need to learn
about waves and particles separately.

The only way you get into trouble is if you /construct/ an
overly-strict definition of wave and an overly-strict definition
of particle ... SO DON'T DO THAT.

This is yet another manifestation of the larger point that
I like to harp on: With rare exceptions, it is a bad idea to
spend time discussing misconceptions. More specifically, it is
a bad idea to introduce a misconception just so you can dispel
it. Instead, it is better to explain the correct conception
and move on. The light shines in the darkness, and the darkness
cannot overcome it.

You cannot explain QM in terms of classical mechanics, and
you should not even try. The shoe is on the other foot: QM
does a fine job of explaining classical mechanics. It tells
you when classical mechanics is valid and when it is not.
Correspondence limit and all that.

Most of QM is not weird. All of introductory-level QM is not
weird. All practical real-world applications of QM are not
weird. The transition from particle mechanics to wave mechanics
is closely analogous to the transition from geometric optics to
physical optics.

QM gets a little bit weird when we start talking about
entangled states aka Schrödinger cat states and EPR.
However, experiments to exhibit such states are exceedingly
hard to set up. Nobody is ever going to stumble across
such a state by accident. There is no reason to even mention
such things in the introductory class.

Note that this general style of bad pedagogy is not restricted
to QM. We see a similar thing in special relativity. In some
circles it is fashionable to deliberately introduce paradoxes
(and then resolve them). IMHO this is just terrible pedagogy.
Specially relativity is *not* weird or paradoxical. It is
just the geometry and trigonometry of spacetime. It makes a
huge number of predictions, most of which are entirely prosaic
and familiar. For example,
a) SR explains at low speeds, the KE is ½ P•V
b) SR explains at high speeds, the KE is P•V (with no factor of ½)
c) SR explains all the intermediate cases!

Without SR, the relationship between (a) and (b) would be
exceptional and hard to explain, and (c) would not be handled
at all. Instead, SR gives a simple, unified explanation of the
whole situation. Ditto for a unified view of electricity and
magnetism. Ditto for a unified view of mass, momentum, and
kinetic energy. Et cetera.


There is always a temptation to tell students that the subject
is more complicated than it really is. This is an occupational
hazard. We must recognize it as such and constantly guard
against it.

I am reminded of the line from "Batman Begins" where Bruce
Wayne says:
"Well, a guy who dresses up like a bat clearly has issues."

In the same way, I would say that anybody who gets to be
a star athlete *or* a physics professor must be somewhat
twisted. It is not normal to have that amount of drive.
There are far easier ways to earn a living. My advice is
to accept the fact that we are all twisted, and to channel
the twistedness into something constructive.

In particular, making the subject seem weirder than it
really is strikes me as the equivalent of the ball player
doing a trashy dance in the end zone. It is a cry for
attention. "Look at what I did; look at me, me, me; this
is really hard and I'm a tough guy because I can do this
really hard thing."

You worry about somebody like that, because if they are
that needy at the personal level, they're probably not
going to be a good team player.

If you want to be a /teacher/, I suggest the non-trashy
approach. "This physics is really easy if you think about
it the right way; let me show you how."

The professor (or athlete) who takes off his clothes is
taking a huge step in the wrong direction. This is way
worse than the usual end-zone dance. This is twistedness
that is *not* channeled into a good direction. I realize
everyone craves attention, but this is the wrong kind of

The highest respect goes to the guy who does something great
/and makes it look easy/.

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