*This World Wide Web page written by
Dan Styer,
Oberlin College Physics Department;
http://www.oberlin.edu/physics/dstyer/StrangeQM/preface.html;
copyright © Daniel F. Styer 1999*

This book presents the two central concepts of quantum mechanics in such a way that non-technical readers will learn how to work simple yet meaningful problems, as well as grasp the conceptual bizarreness of the quantal world. Those two central concepts are: (1) The outcome of an experiment cannot, in general, be predicted exactly; only the probabilities of the various outcomes can be found. (2) These probabilities arise through the interference of amplitudes.

The book is based on a short course (only fourteen lectures) that I have presented to general-audience students at Oberlin College since 1989, and thus it is suitable for use as a course textbook. But it is also suitable for individual readers looking for intellectual adventure. The technical background needed to understand the book is limited to high school algebra and geometry. More important prerequisites are an open mind, a willingness to question your ingrained notions, and a spirit of exploration. Like any adventure, reading this book is not easy. But you will find it rewarding as well as challenging, and at the end you will possess a genuine understanding of the subject rather than a superficial gloss.

How can one present a technical subject like quantum mechanics to a non-technical audience? There are several possibilities. One is to emphasize the history of the subject and anecdotes about the founders of the field. Another is to describe the cultural climate, social pressures, and typical working conditions of a quantum physicist today. A third is to describe useful inventions, such as the laser and the transistor, that work through the action of quantum mechanics. A fourth is to outline in general terms the mathematical machinery used by physicists in solving quantum mechanical problems.

I find all four of these approaches unsatisfactory because they
emphasize quantum *physicists* rather than quantum *physics*.
This book uses instead a fifth approach,
which emphasizes how nature behaves rather than how humans behave.
Humans have certainly been very
clever in discovering and using quantum mechanics, and I am proud of
our species for its activities in this regard. But in this book (except
for the appendices)
the focus rests squarely on nature and not on how we study nature.

In order to solve problems in quantum mechanics, the professional physicist
has erected a gigantic and undoubtedly elegant mathematical edifice. This
edifice is necessary for finding the answers to specific problems (which is,
after all, what physicists are paid to do), but it often conceals rather than
reveals the underlying physical principles of quantum mechanics. Physicists,
in fact, are often clumsy in their use and understanding of quantum
mechanics's central concepts; they are protected from them by a screen of
mathematics. (The very name "*quantum* mechanics" memorializes
an aspect of atomic physics that is not central to quantum mechanics and
that appears in the classical world as well.) This book aims to strip
away the machinery of the edifice and bare
the raw ideas in their naked form.

An analogy helps to explain this aim. The professional automobile mechanic must be familiar with crankshafts and camshafts, pistons and plugs, transmissions and timing. His familiarity enables him to repair cars and earn his salary. Yet these practical and interesting devices are irrelevant to the central concept of how a car works -- which is simply that hot air expands, whence heat from burning gasoline can be converted into motion. Many excellent mechanics are in fact unfamiliar with this central concept. A book on the fundamental workings of automobiles would discuss heat and motion, but would not tell you how to give your car a tune-up. You should expect analogous discussions here: no more and no less.

Above I have described the direct goals of this book. Two other goals
are indirect yet just as important. First, I aim to describe scientific
thought -- its character, its strengths, its limitations -- and to
inspire an appreciation for the elegance, economy, and beauty of scientific
explanations.
Second, I hope to demonstrate the importance and
power of reason as a tool for solving problems and probing the unknown.
The popular press is fond of misstatements
like "the belief in an objective reality,
accessible to reason, . . . suffered a death blow with the advent
of modern physics".
[M. Kakutani, "How technology has changed modern
culture", New York *Times*, 28 November 1989.]
The truth is that
quantum mechanics is unfamiliar, non-common-sensical, and weird,
but it is perfectly logical and rational. Indeed, in the bizarre
world of quantum mechanics, it is logic, and not common sense, that is
the only sure guiding light. In today's cultural atmosphere -- where
in-your-face power play has largely displaced rational debate
in the arena of public discourse -- this point
cannot be overemphasized.

This book describes quantum mechanics as most physicists understand it today. All scientific knowledge is tentative and the pillars of quantum mechanics are no exception. In addition, the experiments and principles described here are all subject to interpretation. I present the standard interpretation, which is not the only one. (I give only fleeting mention to alternative interpretations and formulations not because they are incorrect or unimportant, but because one must have a firm grasp on the standard interpretation before moving on to the alternatives.)

Producing a completely honest yet non-technical account of quantum mechanics is an audacious enterprise, and while developing this treatment I have reached out for help from many people. I need to thank first the 985 Oberlin College students who have, since 1989, taken the course which led to this book. Their questions, objections, doubts, excitement, enthusiasm, and triumphs have inspired many changes -- improvements, I hope -- in the content and presentation given here, as well as in my own understanding of quantum mechanics. In the spring of 1996 I served as associate instructor for the computer conference course "Demystifying Quantum Mechanics", developed and taught by Edwin F. Taylor. Working with Professor Taylor and the fifteen intrepid students in that class (mostly high school teachers scattered across the nation) was a pleasure that further refined my understanding and this book's presentation.

I received helpful direct comments on this treatment from many of the students mentioned above, and from Gary E. Bowman, Amy Bug, Peter Collings, Rufus Neal, Dan Sulke, Edwin F. Taylor, and four anonymous reviewers. This is not to say that all of these readers approve of everything I say here -- indeed, I know that some of them disagree with me on important points -- but I appreciate the contribution that each one of them has made to this work. The illustrations were skillfully drawn by Byron Fouts.

The development of the course which led to this book was supported by a grant from the Sloan Foundation. This acknowledgement may sound like the bland gratitude of someone merely content to receive Sloan's money, but it is not. The encouragement of the foundation, and in particular of program officer Samuel Goldberg, led me to delve deeply into quantum mechanics as a set of physical ideas rather than as an elaborate and somewhat mystical algorithm for solving problems in atomic physics. I have learned much in preparing this account, and I thank the Sloan Foundation for suggesting that someone other than myself would be interested in what I learned.

I invite you to join the community that has developed this approach and this book. Please get in touch with me. I offer you my welcome and my best wishes. Enjoy!