Comment by JumpCrisscross

> Fusion is initiated by bringing nuclei very close one of another, overcoming the electrostatic repulsion

Protons overcoming their electrostatic repulsion doesn't mean fusion--formation of a deuteron does [1]. Protons overcoming their repulsion creates the initial conditions for fusion, but in most cases no fusion occurs. The weak force "chooses" whether fusion occurs or two protons come unusually close and fly apart.

This is a bit of a pedantic line. But nuclear physisist say the weak force initiates fusion because if we take something with as low a cross section as proton-proton interaction to be the starting point of fusion, we might as well extend it to protons being in a star at all. (A greater fraction of protons in a star will fuse than proton-proton interactions graduate to fusion.)

Without the weak force, we have no stellar fusion. Without the weak force, artificial fusion is still possible. That's both a blessing and a curse, since the weak force permits lower-temperature fusion.

> When the input nuclei have enough neutrons

Irrelevant for proton-proton fusion.

[1] https://physics.stackexchange.com/questions/526471/why-is-th...