Why can we never be certain of our scientific theories? The reason i love mathematics and physics is that the rigorous knowledge they impart about reality or what lies beneath it. Yet the more physics I study, the more I realizes how very little we know. What is gravity? what is force? What is inertia? What is time? These type of questions continually nag away at the back of my mind. I have read a great deal of scientific philosophy (such as Popper, Quine, Putnam) and realize that we cannot determine what these things "are" without referring to our own perspective or analogy. I realize that science is empirical, but to me it seems that even empiricism has failings. Assume we have two theories f(x) and g(x) and all our physics observations match both of these theories. Assume furthermore that f(x) and g(x) are mutually exclusive. How do we differentiate between which theory is true? I would assume that the search to differentiate between the two via experimental evidence will continue, but what if there is always two or more theories that may be correct? This really irritates me, as science is my personal quest for knowledge and truth, but it seems to be providing only more questions. I enjoy answering questions, but, and i feel quite embarrassed to say this, I feel frustration knowing that i will never, can never know why or even how the universe works at the deepest levels. I shall die and fade into obscurity without ever achieving the sense of understanding i desire. Do any of the rest of you harbour similar thoughts or doubts? Is there any philosopher who deals with this issue in depth?