The idea of being a millionaire having “made it” stems from the 50s. Adjusted for inflation, that equates to about $10M today. So that’s probably the level to be truely comfortable with F-U money. Health”care” aside.

Yes, gravity is a theory. In scientific terms, theories are proven, repeatable, and accepted. It’s the most robust and strongest form of scientific “fact” we have (since new discoveries can change our understanding, we can’t honestly declare it indisputably factual).

When people say “I have a theory…” they usually mean “I have a hypothesis…” which is some idea or problem statement that is unproven, untested, unverified.

OP was playing off the conflation of those two things.