Re: REFRACTION - REFLECTION

[Leigh Palmer <palmer@sfu.ca>]

> Joel's reluctance is understandable.  Dr. Newbolt is saying essentially
> that internal reflection occurs because we say that it does.  When one
> sets the boundary conditions of a PDE to behave such-and-such a way, one
> should not be surprised that the solution of the PDE corresponds.   That
> is no answer at all to "Why does this happen?", which cannot be answered,
> or "What is the *essential* difference in two different phenomena?".   To
> say the critical angle was exceeded is to say nothing unless the critical
> angle be explained.  Why is it critical?  The reason one gets internal
> reflection is that light and water are magical.  Could someone, now, put
> that in other words?   Perhaps we could pretend that light is waves and
> water is stuff.  Or that light is particles and water is too.   But one
> is going to have to cook  up an analogy that is fascinating, compelling,
> and easily remembered.  Perhaps, on the day following the lecture, the
> class could be asked, "How many related that explanation to someone
> else?"

Physics doesn't explain anything. "Why" questions are a form of
locution that we use by custom, but we know that we don't give
ultimate reasons when we "explain" phenomena. After all, we are in
possession of no ultimate truths!

The central task of physics is to describe Nature, not to explain it.
The "reason" for a particular behaviour is usually an expression of
the fact that it is mathematically consistent with the descriptions
of other, usually more fundamental, phenomena. Even deciding which
phenomena are fundamental can be a subjective call. Giving the
derivation of the Fresnel equations, which follow from the boundary
conditions applied to the Maxwellian fields, those boundary conditions
themselves following in some cases from the law of conservation of
energy, constitutes all the "explanation" you are ever going to get,
unless you know a very well-connected Pope.

Leigh

My question for the day (not invented here): Why are all electrons
identical? Answer: Electrons are identical because we choose to call
anything that is not identical to an electron something else!

(I know, Feynman gave a different answer.)