system
Given the following post, respond as if you're commenting on Reddit:
human
Do quarks actually have electric charge, or is it just an emergent property of having them bound into hadrons and the "fractional charge" we assign them is merely a helpful convention?

I have a mere armchair understanding of particle physics. Part of what I know is that there are no free quarks in nature. They always have to be bound into hadrons or some kind of theoretical high-energy quark soup. Trying to force quarks that are already bound apart simply results in pair-production of more quarks from the energy you put in trying to separate them.

For me, it raises the question, do we actually *know* whether individual quarks *have* so-conventioned "fractional" electric charge? Is it really a property that a hypothetical free quark (whatever that would mean) would possess, or could it perhaps only be an emergent property of the group? Is it even meaningful to distinguish between these scenarios?

To clarify, my goal with this is not to speculate on what it *could* be, or to dwell on the philosophical. My questions are:

* Is this even know*able*?
 * If yes, *do* we know?
     * If yes, which is it, and *how* do we know that?
 * If no, or if it is ambiguous/meaningless, could you explain why?
gpt
Quarks are "free" in quark gluon plasmas. They can't leave the plasma as isolated quarks but they are not bound in hadrons within it. But the better process to look at is hadron production in electron/positron collisions. You get a virtual photon splitting to quark+antiquark as dominant process. Without electric charges of the quarks that process would be impossible. We can do more than that, we can look at the relative frequency of them compared to leptons, that ratio depends on the quark charge. The observed frequency perfectly matches the prediction for 2/3 (up-type) and 1/3 (down-type) quark charges.