>>11106619For what it's worth, I am a phd student that actually understands quantum field theory
The fact that a quark must be combined with one other quark at all times has nothing to do with the quark itself. It is a property of the force between quarks. The force between quarks is very simple (in the sense of being elegant, not easy to understand). It is a natural extension of electrodynamics which you learn in intro physics.
Having to use quantum mechanics is necessary for any particle.
The mass is an arbitrary number, but what would a non-arbitrary mass look like (besides zero)? We can change our units to make the mass be any numerical value we like.
By the way, the 'mass' of a quark is not such a well defined thing. Since it is impossible to completely distinguish the quark from the gluon field that surrounds it, there is no completely clear cut way to define it. If you look at the details of the numbers you look up you will see all sorts of footnotes about these caveats.
