Close enough...

In The Birth of the New Physics, Cohen writes that it is unlikely that Ptolemy actually believed that the planets moved in the complex epicycles of his model and that it was rather just a convenient way to try to predict the motion of the planets. He mentions that modern physicists do a similar thing when they must content themselves with formulas instead of the actual knowledge of how things work. So how much of our knowledge is totally theoretical and conceptual and how much can we practically prove? (since science can't technically "prove" anything as indisputable)