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... If gravity were slightly stronger, all stars would be large, like the ones that produce iron and other heavier elements, but they would burn out too rapidly for the development of life. On the other hand, if gravity were weaker, the stars would endure, but none would produce the heavier elements necessary to form planets. The weak nuclear force controls the decay of neutrons. If it were stronger, neutrons would decay more rapidly, and there would be nothing in the universe but hydrogen. However, if this force were weaker, all the hydrogen would turn into helium and other elements. The electromagnetic force binds atoms to one another to form molecules. If it were either weaker or stronger, no chemical bonds would form, so no life could exist. Finally, the strong nuclear force overcomes the electromagnetic force and allows the atomic nucleus to exist. Like the weak nuclear force, changing it would produce a universe with only hydrogen or with no hydrogen. In sum, without planets, hydrogen, and chemical bonds, there would be no life as we know it ...