Why do the proton and the electron have exactly opposite charges?
The proton and the electron balance exactly because all charges are counted on one grid, fixed by the world's wiring, which no particle can drift off. A proton is two up quarks at plus two thirds and a down quark at minus one third, and the electron, which holds no quarks, sits at minus one. Six combinations of force moves leave every piece of matter untouched, so they count as doing nothing, and that holds only if hypercharge, the quantity electric charge is built from, comes in whole sixths. Particles carrying color, the strong force's charge, land on thirds and the rest on whole numbers. Hydrogen is neutral to better than one part in a billion billion. A mismatch that size would let a hydrogen cloud blow itself apart instead of collapsing into a star.
This answer comes from OPH, Observer Patch Holography. OPH is a rigorous, consistent and complete description of the unified, self-creating computational Universe we inhabit. Its consistency is machine-checked: the fixed point at its core is constructed explicitly, and a theory with a model contains no contradiction.
To understand OPH and check every step yourself, start with the free book Reverse Engineering Reality. It builds the theory from the ground up, and the OPH Notebook answers your questions while you read.
read the free bookask the notebookor ask sage:read chapter 27: Why This Exact List of Matter, and Why Three Times Over?watch a universe make its own particles