Why we owe our lives to the neutron

[probus]

Force is sometimes uncountable, but in this sense we are comparing and contrasting forces, so the noun needs to become countable. We have, for example, the set phrases "force of habit" and "force of nature." In the first, force is uncountable. But the implication of the second is that Mother Nature has more than one force at her disposal, among them the strong and the weak nuclear forces.