Do most of you really consider ray tracing to be "physics"?
That's like asking whether a harmonic oscillator is "physics".
I take it as axiomatic that:
No matter what you are doing, you can always do it wrong.
As a corollary, I'm sure that ray tracing can be done so badly
that it is devoid of physics ... but so can anything else.
On the other hand ... ray tracing is the most elementary way of
introducing ideas of phase space and Liouville's theorem ...
which is one of the most top sacred things in "physics".
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True story: For a couple of years starting when I was about 13
years old, I wanted to build the ultimate "rich field telescope".
I wanted to build it with so much light-gathering power that
you could see the Rosette nebula in the eyepiece (as opposed to
making a long exposure on film).
I worked out the design on paper. I tried everything: big
aperture, short focal length, lenses, mirrors, you name it,
but I could never get the brightness anywhere near what I
wanted.
-- I was too clueless to realize that I had "discovered" a
corollary to Liouville's theorem. It turns out that even
if you were standing in the middle of the Rosette nebula,
it would be too dim to be been by eye, and no amount of
optics will ever make the view brighter than that. I
didn't figure that out until years later.
-- At least I was smart enough to do the design on paper,
and to trust the results of the calculation. Since the
design failed on paper, I knew not to spend resources
trying to actually build such a thing.