🚀 go-pugleaf

I wrote:

  I believe it is intellectually honest to tell high-school
  students that Planck's black-body formula, and the photo-electric
  effect, and a bunch of other stuff, lead to our current picture,
  which explains a wide range of phenomena remarkably well.

And Martin Green replied:

    If it's the Compton effect which demonstrates that light is made of
    particles, then why is it "intellectually honest" to tell high school
    students that the photo-electric effect cannot be explained by classical
    waves?

Note that we do not contradict each other, appearances
notwithstanding.  I agree that it is wrong to say that the
photo-electric effect cannot be explained by any theory that includes
classical waves as a component.  And if a high-school textbook or
teacher says this, knowing it's false, then I agree that is
intellectually dishonest.

Moreover, I am told some folk still believe classical E&M will make a
come-back.  We have the proponents of Stochastic Electrodynamics
(SED), and of Neoclassical Electrodynamics (NED).  (Check DejaNews for
some old s.p.r. posts about these.)  I don't know enough about either
of these alternatives to make a judgement.

BUT: scientific proof differs from mathematical proof!  Consider the
etymology of the word "prove", from "probare", to *test*.  My on-line
websters says for "prove":

1 archaic: to learn or find out by experience
2a: to test the truth, validity, or genuineness of <the exception
     proves the rule> <prove a will at probate>

Meaning (1) may be archaic, but it's quite relevant for science--- as
is (2a).

Why do nearly all present-day physicists believe in photons?  Well,
the complete historical tale is tangled (as usual), and historians
argue over aspects of it (ditto), but I think just about everyone
would agree on a few highlights:

(a) Planck puts forth his black-body formula
(b) Einstein finds an especially simple derivation of Planck's
    formula from his light-quanta hypothesis
(c) Einstein predicts that the photo-electric effect should satisfy
    the formula E = hf - W_0
(d) Millikan, much to his amazement, confirms Einstein's prediction

Now, that may not have clinched the matter for contemporary
physicists, but after (d), the photon hypothesis sure had a lot more
currency than before.

In a phrase, conceptual economy.  The photo-electric effect made the
photon hypothesis highly plausible.  A wealth of subsequent research
(theoretical and experimental) consolidated its position.

Compare and contrast:

    "Young's diffraction experiments lead to increased acceptance for
    the wave theory of light.  Other scientists built on Young's
    results, until the wave theory was generally regarded as correct
    by the end of the 19th century.  (We will discuss Maxwell's
    contribution in the next chapter.)"

No mention of Fresnel or the famous "white spot" experiment, not at
this level of detail.

    "Einstein's explanation of the photo-electric effect lead to
    increased acceptance for his idea of photons.  Scientists remained
    disturbed though about how to reconcile this theory with the
    successes of the wave theory.  Eventually quantum mechanics was
    proposed; according to quantum mechanics, light has both particle
    aspects and wave aspects.  We will not be able, in this book, to
    explain quantum mechanics in detail, but we will sketch the main
    ideas.  Quantum mechanics today is generally regarded as providing
    the correct theory of light."

No mention of the Bohr-Kramers-Slater proposal, or the Compton effect,
or the Bothe-Geiger experiment, or Dirac's theory of radiation, or
modern "tagged photon" experiments, or SED or NED at this level of
detail.

Now I just made those "textbook passages" up, and *I* regard them as
intellectually honest.  How about you?