Degeneracy pressure is why the whole thing is stable against gravitational collapse, but I don't think it's why individual neutrons don't decay. (I'd say what i

Degeneracy pressure is why the whole thing is stable against gravitational collapse, but I don't think it's why individual neutrons don't decay. (I'd say what is if it weren't for the trivial obstacle that I don't know. Handwavily, I think it's often the case that large ensembles of particles can get into nice stable low-energy states for subtle quantum-mechanical reasons.)