Nothing in the real world has ever been rigorously proved, or ever will be. Proof, in the mathematical sense, is possible only if you have the luxury of defining the universe you're operating in. In the real world, we must deal with levels of certainty based on observed evidence. The more and better evidence we have for something, the more certainty we assign to it; when there is enough evidence, we label the something a fact, even though it still isn't 100% certain.