Where, when, and why did the notion of conservation of energy become a law? I know that we are able to "invent" new means of "fixing" any apparent violations of this and further I understand that the new inventions of other energy forces have led us to new ways of seeing the world but I still don't understand why this is deemed a law. I think it is more of an axiom which means it is a given within our problem solving. Couldn't we have just as easily put causation (and only allowing forward time travel to exist) as an axiom and then simply found "fixes" to any violations to this concept similar to conservation of energy axiom that we all appear to simply accept without proof ? Thanks in advance for any comments on this subject.