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Re: [Phys-l] Question about Quarks and the Standard Model


I spend the first quarter of my intro physics class for majors "building"
the standard model. I find it a wonderful way to convey the ideas of
*doing* physics to the students (we subtitle the course "How to Think
Like a Physicist"). I take a quasi-historical approach, starting with
the discovery of the electron in 1897, and then lead them through the
"particle zoo" (their table of particles keeps getting longer and longer
and longer... and then collapses down to u, d, and s :-)). The beauty of
this is two-fold: first, it blows their minds about what they think
*is* (we spend about a week on nuclear binding energy to explore why a
neutron on its own decays but only some neutrons in some isotopes decay,
why an alpha particle isn't just a proton, like a beta particle is just
an electron, and that *really* blows their minds! It also lets me talk
about stellar nucleosynthesis, supernovae, and how we're all stardust,
which is also fun). They *love* playing with the cloud chamber. Second,
it lets me explore fundamental ways of thinking in physics without
they *get* calculus (many of them are just taking calculus concurrently).
I find just starting with mechanics leads to all kinds of confusion
they don't get derivatives and integrals yet, so trying to talk about
velocity, and acceleration leads to much confusion and frustration. We
a lot of time on model-building, falsification, hypothesis testing, the
provisional nature of scientific knowledge, the crucial role of
conservation laws, symmetries, the limitations of perception, confirmation

bias, and how to look for patterns. To determine whether or not a Xi- can

decay into a proton, you don't need calculus, you just need to be able to
charge numbers, strangeness numbers, and baryon numbers. One of my
class sessions is when we explore physical and mathematical models for
decay, and they have to wrap their brains around the fact that flipping a
thousand pennies multiple times, removing the heads each time, does
describe how subatomic particles behave. We had a great discussion about
what "*really* random" might actually mean as opposed to "apparently
and how you might go about telling the difference.

So, to answer the original question, pedagogically, it's not the quarks
themselves that are of interest to me. Whether they remember that there
are six quarks, and they're called up, down, strange, charm, etc. is less
important to me than the hope that they get a vision for how to *do*
and how doing science is a different way of thinking about the world than
most other kinds of hermeneutical matrices. Quarks let me specifically
explicitly undermine the kind of thinking that says "memorize these true
facts" and talk about models being "not wrong", or "accurate within the
uncertainties", and I relish taking the classic model of the atom that
all know (with the little red and blue balls clumped together in the
and the electrons moving around it in little circular orbits) and
demolishing it. Sometimes I give them an exam question where I put that
image on the page and ask "Tell me five things about this picture that are
wrong." Every year, someone asks "so, are these quark things *real*, or
this just a handy book-keeping device to explain the particles?" Then I
get to grin maniacally and ask "what is real? How would you tell the
between a model that was *real* and a model that *just worked*?" Leads to
all kinds of fun discussions. ;-)

Next we're doing special relativity, and I can blow their minds about how
space, time and simultenaity are not what they thought. :-)

Hope that was helpful. Please let me know if I can explain anything in
more detail.


Don Smith
Guilford College Physics Department