We, in this modern world, have become very specialized people. That
means we have also become very interdependent. Within the last
century, our change in this direction has become particularly rapid.
By the beginning of the 1900s, it was already becoming impossible for
any person even to know about all the things that were
understood somewhere within his society. Now, near the end of the
century, in an era of global
communication, human knowledge is so specialized and grows so rapidly,
that even expecting to keep up seems farfetched. And simply
knowing about something is a far more modest goal than understanding
it well enough to use the best of what has been learned. Yet somehow,
out of this vast store of knowledge, we must cull the part that is to
serve as our basic, day-to-day working understanding, our on-hand
intellectual resource. Our Culture is the medium we build to protect
that central kernel (and hopefully the more specialized parts, too),
and to make it available to each new generation. What we enable and expect our Culture to teach us is increadibly important in
shaping who we are and how we are able to live.
Generally, we would like our common knowledge to do two things for us. First, it should provide a strong base for communication, which makes our interdependent effort as fruitful as possible. Even with good communication, though, interdependence entails a certain burden of complexity. Therefore, we would also like our common knowledge to make us, in appropriate ways, more independent, so that we do not overload our relationships, doing collectively what we could more easily do for ourselves. Indeed, there are some valuable parts of life that can only begin in independent action and independent thought, as we shall see. At the same time, knowing things should bring pleasure in itself, and not just be a means to some other end. It is not a secondary consideration that in both of these areas we would also like what we know to make the experience of day-to-day living as rich as it can be.
This book is motivated by a belief that physics should be a central
pillar of any person's common knowledge in the modern world. A claim
like that requires some explanation, and also some justification,
because on the face of it, it seems a lot to ask. It is likely that
no field reaches further, or contains more specialized
knowledge, than Physics.
What, then, among all the modern specialized branches of
knowledge, makes physics so special that we should assign it central
importance? The purpose of this first chapter is to answer that
question. It is intended to explain what physics is, as a formal body
of knowledge and as a practice, how it affects our lives already, what
it can tell us about the natural world and about ourselves, and what
that understanding can do for us.
We will discover that much of what physics has to offer lies outside the formal body of knowledge that could be called Physics proper, and yet is probably impossible to get across without it. In the process of building the formal body, the hard and shining core of physics, people have learned to think in new ways, which have shaped the practice and grown together with the formal knowledge at the same time. The two have influenced each other so centrally, and in such important respects, that it has become rather impossible to use parts of Physics-as-knowledge, without also understanding the essence of physics-as-practice. Further, each aspect is valuable, to us as people, in its own right. As we explore these relationships more fully in this chapter, we will also see how to plot a course through topics, which will communicate what has been learned, and how it can be used. The following chapters will then develop those topics in more detail.
In a narrow sense, the subject matter of this book could be called Modern Physics. Certainly it contains descriptions of some of the most recent discoveries people have made about the behavior of nature. At the same time as new discoveries have been added to Physics, though, very old knowledge has come to be understood from modern perspectives. Often these perspectives are first made possible precisely by the advances in Physics. The modern perspectives are valuable in their own right, though, because they can give new order and simplicity to what was known before. While the specific ``knowledge'' of the past may not be changed, a newly visible order in how its parts relate can make them much clearer and more powerful ideas than they were when they were first created. In that sense, this book is also about Modern physics which is very old. One part of a modern perspective is its judgement of what has proven useful or fundamental, and the simplification that comes from thinking about topics according to that order. Therefore, while this is a book about modern ideas, it is also intended to start from something like a beginning. The modern world didn't spring into being out of nothing, and its ideas are really not best discussed by jumping into them in the middle. One of the most important aspects of Modern physics that we hope to convey is its sense of continuity, and its remarkable coherence across all of what has been understood, because much of that coherence has become visible for the first time, only within the last several decades.
In two senses, then, the book purports to address a ``big picture''. One sense, which will become clear as we proceed, is how much a discussion of Physics really needs to include its relation to the people who use it, because most modern discoveries cannot even be understood out of such a context. The dependence is so deep that it even underpins the language in which Physics is thought and expressed. The other sense in which modern physics is a big picture is this way that it contains everything that went before, and gives it new meaning by exposing new order or recognizing new significance in old ideas. It probably makes no sense, though, to think of either picture as nearing any sort of ``completion''. At each stage in history, we can summarize what we have learned up to that point, and what order that has enabled us to place on everything that went before. Thus a review of modern physics, even when it includes what we have learned about how we ourselves think, can at most be a current update, a snapshot of what we know at some moment, and what kind of people that knowledge makes it possible for us to be.