Great changings in the way of thinking and the technological achievements are mostly characterized by an important scientific publication in a century that changes everything in that century. We can recognize the century of Isaac Newton who triggered in 1687 the large changings in thinking with his famous publication “Philisophiae Naturalis Principia Mathematica” (Mathematical Principles of Natural Philosophy). We recognize the century of James Clerk Maxwell who triggered in 1865 the large changings in thinking with his famous publication “A Dynamical Theory of the Electromagnetic Field”.When we look at todays Physics, we can only be impressed by the enormous amount of knowledge and a complete New World of technical applications that has never been in the world before. We now live in the century of the impressive victory of the new science and the new technology over the old-fashioned world and the old-fashioned way of thinking. But one little misunderstanding in one of the classical fundamental mathematical building blocks in Physics can change everything we know in todays modern Physics.