The Weak Force
nHolds neutron together.
uNeutron decay: half-life 13 minutes
uNeutron Þ Proton + Electron + Antineutrino
nFew % weaker, then few n, little He, few heavy elements; even these stay trapped in stars.
nFew % stronger, then many n, too much He, too many heavy elements; but these, too, stay trapped in stars.
nThe weak force is tuned to a few percent.