The last two chapters have tended to be a bit abstract. Their purpose was to serve as guideposts, pointing out features and important consistencies in what follows. Thus they naturally dealt with generalities. It is expected that much of what was said in the first two chapters will not really aquire depth until all of the subsequent chapters have been digested somewhat, but hopefully they can provide some sense of orentation as that is being accomplished. In this chapter, for the first time, we can begin to talk about specific details.
Suppose you want to go from knowing little or nothing about physics, to having some understanding of what physics is and what it can be used to achieve, how physicists go about actually figuring things out, and how to make sense of the results they report. How should you proceed? One approach would be to study physics historically, and trace through discoveries in the order in which they were actually made. This approach tends to be haphazard, because it follows the meandering and accidental course in which expceptional people happened to notice things. Many of the organizational points that make an overview of the subject simplest would not even become visible until the very end, after all the details had been examined, if even then. An alternative approach would be to start from a logical rather than a historical beginning, building an understanding of physical descriptions in a hierarchy from the simple to the complex.
This essentially mirrors the approach physicists use in coming to understand the patterns of nature, in each problem they solve. Thus by following through any typical problem as a physicist would actually solve it, and making note of what is being done at each stage, one learns about physics in essentially the same way physicists learn about nature. It is this search for a logical starting point in physics that brings us to the topic of this chapter.