Re: cathode rays - historical question

["John S. Denker" <jsd@MONMOUTH.COM>]

On 04/06/2003 12:48 PM, Mark Sylvester wrote:
> The answer affects how I teach the background to the discovery of the
> electron. There is already the wave/particle discussion about light. If
> there is good reason to mention differences here then I want to do so. In
> fact, I have for years talked about a particle vs continuum debate, and am
> wondering if I've been wrong all this time.

The pedagogical question is central.

IMHO the so-called wave/particle "debate" gets too much
emphasis in many classrooms.  Why bring it up at all?

1) In general, the history of physics is a poor guide to
the teaching of physics.  Kuhn had something to say
about this.  Typically the "historical" approach leads
to a distortion of the history and sometimes a distortion
of the physics as well.

The history of science is an _advanced_ topic, open
to those who already understand physics and already
understand the methods of historical inquiry.

Students have a limited time budget.  Historically,
the facts were discovered in convoluted and difficult
ways.  The best evidence nowadays for the nature of
electrons doesn't come from Thomson's experiments.
Why not give the students the best evidence and
leave it at that?

2) It has long been known (deBroglie 1924) that there
is no real distinction between the physics of waves
and the physics of particles.  So why foist on the
students a false and useless distinction?

I like to say there is just "stuff".  Sometimes stuff
exhibits wavelike properties such as superposition.
Sometimes stuff exhibits particlelike properties such
as quantization.  Sometimes both.  There's nothing to
debate.

Quantum mechanics is a little bit weird, but it's
not completely weird, and there's nothing to be
gained by making it seem weirder by introducing
extraneous confusing concepts or "debates".

I've never seen much credible evidence of a "debate"
that could have affected Thomson, not after Young
(1801) and expecially not after Hertz (1888).
According to deBroglie,
http://www-gap.dcs.st-and.ac.uk/~history/Mathematicians/Broglie.html
it started out as a simple dichotomy: matter was
particlelike and radiation was wavelike.  Later
there was a gradual accumulation of evidence that
radiation was quantized, but this was never strong
enough to make anybody discard the wave description
of radiation.  And Thomson neither benefitted from
nor contributed to this evidence.  Also remember
that Thomson was only one of many people whose
experiments and ideas shed light on the nature of
the electron.  He contributed neither the first
estimate of the electron e/m ratio nor the first
estimate of the electron mass.

http://www.aip.org/history/electron/jjrays.htm
http://www.nobel.se/physics/laureates/1906/press.html

If you're going to do history, do it right.  Even
then, remember it is usually not a good guide to
teaching the facts and concepts of science as presently
understood.  And it's not even a good guide to how
science should be done;  past scientists have made
plenty of mistakes.