With these perspectives and motivations in hand, we embark on the rest of the topics in the book.
Clearly, the first of these must be language, in Chapter 2. Next, in keeping with the order in which physicists actually solve problems, we will look at notions of scale. This includes the formal topic of Dimensional Analysis, in Chapter 3, and some remarkable natural features known as the fundamental constants, in Chapter 4.
Only after these, beginning in Chapter 5, will we be ready to explain exactly what Newton did, and how it is used. Chapter 6 introduces a remarkable tool called the Principle of Least Action. It was first introduced as a calculating method, to make certain problems more tractable than Newton's method did. In modern times, people have found that it unconvers one of the most important of all physical notions, that of symmetry. Chapter 7 presents the classical notion of a field, which is our first exploration beyond the strict language of single objects.
These ideas, though modern in the way we use them, were all discovered well before the beginning of the current century, or the other ``modern topics''. They are cornerstone ideas of modern physics, more powerful and coherent now than when they were invented. As the ``old part'' of modern physics, though, they are usually thought of as classical ideas. These comprise Part I.
Part II deals with Relativity. Before we can even discuss the topic, we will have to go back, all the way to the level of language. A brief synopsis of what we will find is given in Chapter 8. Then, Chapters 9 and 10 treat two aspects of the restricted, or special aspects of Relativity. These are divided as kinematics and dynamics, along lines similar to those we will use in Part I.
Then, making deep use of fields for the first time, we will encounter Maxwell's magnificent Theory of Electromagnetism in Chapter 11. This will be our first example, after Mendeleev's chemistry, of real progress toward unification. Historically, it motivated Relativity, though we will discuss it after having described the special part separately. We choose this order because Maxwell's Electromagnetism is, from start to finish, the paradigm after which Einstein's complete, or general theory of Relativity was formed. That is the topic of Chapter 12.
In Part III, we encounter the Quantum Theory. While the discoveries in both Parts II and III occured logically and historically after the classical ideas of Part I, there is no sense in which Quantum Mechanics ``follows'' Relativity. (Curiously, some day there may be.) Historically, both fields developed side by side, with contributions from many of the same people. However, it is easiest to keep each topic as its own group, and Relativity is placed first because, in some sense, it requires a ``less radical'' revision of language than does Quantum Mechanics.
Again, we begin Part III with a step back: a tool-building chapter (13) that covers a very old classical idea called Huygens' construction, and a long-known property of many wave systems, called Superposition. While Huygen's construction is very old, it was not regarded as anything really fundamental until it appeared, very recently, in the Quantum Theory. With this tool in place, we will then discuss the experiments that led to Quantum Mechanics in Chapter 14, and the Theory that made sense of them in Chapter 15. Chapter 16, on Particle Physics, brings us to the most recent discoveries of modern times, and the highest current unification of ideas we have. It employs Huygens' construction and all the concepts of Relativity and the Quantum Theory. However, it also assigns a whole new importance to the notions of Symmetry and Conservation, from Chapter 6, and explains the next refinement of the notion of the Classical Field from Chapter 7. Most of the significance that we now assign to the fundamental constants has also come from their rôle in this theory. Indeed, the creation of particle physics within the last five decades was the step that laid most of the coherence on modern physics that exists today. It also defines the language within which our current theory of fundamental processes is phrased.
Each of the chapters is accompanied by various exercises. Some of them are fairly restricted, and try to deal only with material entirely within those chapters. Others are more general, making use of topics throughout the book, and others are so general that they are just intended to be explorations of what can be understood about everyday life. After all, that is the point of doing physics. Very many of the problems are devoted to the process of simplification and ordered approximation in physics. These are called Fermi Problems, and are introduced (with examples) in the context of Dimensional Analysis in Chapter 3.
A few of the problems in the book, the so-called ``seminal problems'', are special. In some sense, they should be considered part of the text itself. They contain special results that should be calculated by the reader, whether because they represent slight tangents from the main line of development or because the are simply so remarkable to do. The answers reached through them will never be strictly necessary to follow the main text. However, they contain results that are so important, and give such a better understanding of the main points, that the text would be greatly impoverished without them.
The material in this chapter has been intended as a road map. All the rest of the chapters are intended to make meaningful things that could only be laid out here. A road map may tell which cities lie along a route, and even which route is a good one to take, but knowing that alone is no substitute for making the trip. Thus, most of the points stated here should not yet be clear, much less convincing. On the other hand, they are points that should be recognized ahead of time. Hopefully that way they will be recognizable when they come up in the chapters that follow.