= Why do the electron and the proton have the same charge except for the opposite signs?
https://physics.stackexchange.com/questions/21753/why-do-electron-and-proton-have-the-same-but-opposite-electric-charge
Given the view of the <Standard Model> where the <electron> and <quarks> are just completely separate matter fields, there is at first sight no clear theoretical requirement for that.
As mentioned e.g. at <QED and the men who made it: Dyson, Feynman, Schwinger, and Tomonaga by Silvan Schweber (1994)> chapter 1.6 "Hole theory", <Dirac> initially wanted to think of the holes in his hole theory as the <protons>, as a way to not have to postulate a new particle, the <positron>, and as a way to "explain" the proton in similar terms. Others however soon proposed arguments why the <positron> would need to have the same <mass>, and this idea had to be discarded.