nHolds atom together, also molecules.
nBoth repulsive & attractive, due to existence of positive & negative charges.
n+ and – charges must be almost exactly equal in number, to better than one part in
nYet protons (+) and electrons (-) drastically different in mass, and froze out at
quite different times in the early universe.
nIf not for this equality, e-m would dominate gravity, so no galaxies, no stars, no
nE-m is tuned to one part in 1040.