How do we know what we know?

[Aegon]

We can trust in the knowledge of that which withstands the scrutiny of empiricism.  Anything else would just be subjective conscientious fancy.

You mean a process created by the human brain and performed by the human brain? It doesn't change the problem I outlined in the beginning of the OP

Even then, an empiricist can accept one thing, and then 50 years when research develops and we realize that that one thing is false and a new thing is true, the empiricist was guilty of calling something a fact that wasn't. Not that I blame them, because I'd be in the same boat. If what we firmly think is true now is shown not to be in 50, 100, 150, etc. years... then that surely can't be objective knowledge or truth because we know it wasn't. So why call today's facts facts? 

I suppose that's why we call very convincing scientific theories "Theories" regardless of the insane amount of evidence, but how many of us forget to be humble and assume what we think is true today is really, truly, objectively true?