[tocomment]

I saw that page. It still doesn't really explain it except to say that one neutron can only exist for 15 minutes by itself. But wouldn't putting multiple neutrons together prevent that?

Or is it something about being around protons that prevents neutron decay?

[InclinedPlane]

The strong force isn't like gravity, it's a 3 color force that is far more complicated than any other. From what I understand, neutrons just don't stick to each other (note that neutron stars are held together by gravity).