[Domino]

(edit: Well, my reply sure came later than I thought it would... :) )

His question leads to a valid point: if we claim to have multiple unique, indivisible particles, one must wonder what gives them their uniqueness. By what mechanism is a quark different from a lepton? They say that quarks change flavor in the nucleus through the exchange of gluons, yet, if a quark is the smallest, indivisible unit of matter, how does a gluon change anything about it?

The whole point of the atom was to be the smallest indivisible unit of matter, from which all else was constructed. Since then, we have learned that what we called an atom is not really an atom, since it can be further divided. However, instead of renewing the quest to find the smallest indivisible unit of matter, we have simply accepted that there are some dozen, or more, unique forms, all of which are indivisible. Where once logic demanded that everything be made of some thing, with differing properties achieved through different arrangements of that thing, we now accept that everything is made from a dozen somethings, and the mystery stops there. No need to look for smaller parts to explain differing properties: these dozen things are simply, inexplicably themselves.

Of course, that's easy for quantum physicists to accept, because they've all accepted that there's no reason to expect logic to apply on that scale. If it turns out that we can explain the universe with Itchies, Scratchies, Hammers, and Dynamites, that's just the way it is, don't look behind that curtain...