alt Hacker NewsOr why the quarks that make up protons and neutrons have fractional charges, with +1 protons mixing two +2/3 up quarks and one -1/3 down quark, and the neutral neutron is one up quark and two down quarks. And where are all the other Quarks in all of this, busy tending bar?
They have fractional charges because that is how we happen to measure charge. If our unit of charge had been set when we knew about quarks, we would have chosen those as fundamental, and the charge of the electron would instead be -3.
Now, the ratios between these charges appear to be fundamental. But the presence of fractions is arbitrary.