What are the "opposites" of the weak force, or the strong force?

You seem to misunderstand my point. I'm by no means saying we know everything about gravity. However, the more and more data we gather, at scales ranging from larger than galaxies to subatomic, the less space there is for huge surprises to pop out.

As an example, there are certainly countless insects I don't know about in our apartment, probably some mice, maybe even some rats, but if you told me there was an elephant here, or even just a lion, I'd be skeptical, because there's just no room for it.

If you recall, this discussion comes from an article where we were talking about magical gravitational cancelling technology. I still stand by my warning - it is quite likely though of course never certain that this technology will never exist.