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Re: REFRACTION - REFLECTION



Leigh Palmer says:

Fermat's principle doesn't explain anything. It is a valid
model for the propagation of light, that's all. Physics
doesn't explain; it can only describe. It is a good idea to
keep this fact always in the front of your mind. Not doing so
is the cognitive error which makes the religious believe they
have all the answers.

On the contrary, physics frequently explains... in terms of more
fundamental (i.e., more general) concepts. It is that last phrase that
differentiates physics from religion; physics doesn't claim any ultimate
explanation, only relative ones.

And that's why many of us find Fermat's principle unsatisfying. It doesn't
explain in either sense. It's just a functional model. (Before I offend
someone into defending Fermat's principle, let me say that I am referring
to the simple statement of it as given earlier in this thread. I'm sure
that a deeper study of the principle would be interesting and rewarding.)

Devil's advocate: But Fermat's principle *is* a "more fundamental
concept". Why doesn't it constitute an explanation?
Answer: That's well illustrated by the following:

The rays always choose the path which minimizes this transit
time. This analogous as to why a cross country auto traveler takes the
bypass (rather than going straight through downtown) around a city which is
between the traveller's point of departure and destination when the
traveller approaches the city during rush hour.

David Bowman

This is of course not an explanation, just an anthropomorphic analogy. But
it suffers the same problem as Fermat's principle: it seems to require that
the light have a foreknowledge of the territory ahead, which doesn't seem
to make much sense. Now maybe it is possible to rearrange your world-view
in order to get around this. However, our hypothetical student isn't about
to change their world-view without a lot more instruction.

--
--James McLean
jmclean@chem.ucsd.edu
post doc
UC San Diego, Chemistry