How and where should you explain how the laws of your sci-fi universe significantly differ from the real world? Let's say that the laws are so different from the what be construed from the theories of quantum physics and general relativity. How do you explain this and where? I thought using the preface would be a good idea, but what if the preface needs to be as long as 10 chapters to fully explain the differences? I am thinking there's a better way of doing this.