Re: photelectricity, history, and PAC Learning

[Jack Uretsky <jlu@HEP.ANL.GOV>]

        If John's point is stated in his first paragraph, then I think
that I disagree, as follows:

On Wed, 8 Nov 2000, John Denker wrote:

> There has been some discussion of whether it makes sense to analyze the
> photoelectric effect from a "19th-century physics" point of view.  This has
> led to discussion of point such as
>          -- when was the cathode-ray e/m ratio first measured
>          -- when were work functions first measured
>          -- et cetera
> This will at best lead far afield, and at worst will lead to quite a messy
> morass, as discusses further below.
_______________________________snip_______________________________________

        I would replace the final clause with:
"at <hopefully> will lead to quite a messy morass."
        I think it important to convey to students (and the public) the
knowledge that the progress of knowledge is "quite a messy morass".
Much of our time is spent pursuing false leads and developing erroneous
principles.  Only rarely does a new insight lead to a confirming set of
experiments that permits us to settle upon a new paradigm.
        But history is important to the practitioners because it provides
us with a cultural memory that helps us to recognize the repetition of
old patterns.  One example: Rutherford's realization that a large
back-scattering cross section indicated the existence of a central core.
History repeated itself when the deep inelastic scattering of electrons at
SLAC was interpreted as showing the existence of a quark substructure in
the proton.  Memory of Rutherford's experiment facilitated the
interpretation of the SLAC experiments.
        My point: I think it useful (and fun) to see how our predecessors
stumbled and fumbled.  And I can feel rewarded if, on occasion, I can see
my colleagues repeating ancient patterns.
                                        Regards,
                                                Jack