How do we know there isn't a "weak gravity" force?

We've only ever existed in a field of "strong" gravity. How do we know we aren't living on a "proton" and the gravity we feel is just the "strong gravity force"? I've heard the universe is expanding, what if matter starts repulsing itself at certain distances similar to how the strong and weak nuclear forces work, but we can't experience it because we've only existed within the field of the strong gravity force