Knowledge can also comprise the after effects of actions or events. If this...then that.
You experiment. You get results. You attain knowledge.
Experimental results have seemed to back up some conclusions we know now are false. Experimental test after experimental test told us calculus perfectly explained the motion of objects in the universe. Turns out that it doesn't quite do so. So we have relativity. Relativity perfectly explained the motion of objects in universe. Well... not quite, because it breaks down in high-gravity situations....
The only real facts we tend to obtain from experimentation is that what we "knew" to be true yesterday, turns out to be wrong. (That does have something to do with the nature of experimentation. It's impossible to absolutely prove something, and by comparison it is easy to disprove it.)
To comprise a "theory" under scientific definition the theory must explain all observations, and all future observations must match the theory.
Before Hubble (Edwin, not the telescope named for him), everyone KNEW the Universe was static. It might not be infinitely old, but it was unchanging. Then Hubble discovered that the Universe was expanding. This idea was so offensive to Einstein, one of the greatest minds of all time, that he invented a "cosmological constant" that countered this expansion. (He would later acknowledge this as one of the greatest mistakes of his career.) Further, Einstein hated the idea of quantum mechanics because "God does not play [dice] with the universe."
Every idea we have ever had is wrong, and every "truth" we cling to out of desperation, fear, or faith, is only a part of a greater truth.
I don't know what that greater truth is though.
And I knew someone would bring up Socrates, which is precisely why I didn't bring him up. Consider this. He knows that he knows nothing, so he knows something, but if he knows something, then he doesn't know nothing, which means that his knowledge that he knows nothing must be wrong. So he knows nothing. But if he knows nothing, than his knowledge that he knows nothing means that he knows something....
Leaving that little infinite loop aside, remember that Socrates believed that nothing in the world was real in the way that we perceive it. (Oh great, the cave
Because we lack perfect instruments (and because the universe lacks perfection) none of our observations are absolutely correct, which means that there is no absolute truth to be had. We can conceive of these absolute truths, just like we can conceive of perfect circles, but there is no such thing. (Planck distance, look it up. Any "perfect circle" is a convex shape of finite sides, each of the Planck distance in length.)
There is no truth.
1) If there is no truth
2) Knowledge requires truth
3) There is no such thing as knowledge.
EDIT: Left out the concluding part. So, either there is no knowledge, or knowledge doesn't require truth. Which means we can know things that are wrong.