A hypothetical question: Say that Newton's constant G is increased a bit during the period between weak interaction decoupling and the time when photodisintegration becomes ineffective, and the helium is formed. (I.e. during the period when neutrons just decay). Would that give a larger or smaller abundance of helium compared to "normal"? Intuitively one might think that increased G leads to increased gravitational strength and therefore halts the expansion more, and thus it would take a longer time for the rate of photodisintegration to drop below the expansion rate (i.e. more time for neutrons to decay, and hence smaller helium abundance). On the other hand the Friedman eq say that the expansion rate increases with G, and thus would lead to a shorter time for neutrons to decay (i.e. larger helium abundance). So which is correct?