quote:When I were a lad, my maths teacher insisted that equations were accompanied with a "given" list that explained all the detail of the data and functions applied to it. The emergence of quantum and relativistic math from their classical root currently seems to ignore this discipline of "full disclosure".
The principle came out of classical and was then incorporated into Quantum and Relativity. I view it as an example of holism ie the whole is greater than the sum of the parts. You can see the parts but how they all link together requires integration ie an intuitive leap. It does make things easier once you have the Action function because you then deconstruct to get the answers to test against measurements.
In quantum there was another leap which was to define the probabalistic wavefunction and relate it's space and time derivatives to classical momentum and energy. Then Dirac relativised it and then least action was used for Quantum electro dynamics see this.
It works but Feynmann said "I think I can safely say that nobody understands quantum mechanics." so we're in good company.