Table of Contents
Title Page
Copyright Page
Dedication
Introduction
SECTION 1 - TALES TO ASTONISH
CHAPTER ONE - Quantum Mechanics in Three Easy Steps
CHAPTER TWO - Photons at the Beach
CHAPTER THREE - Fearful Symmetry
CHAPTER FOUR - It’s All Done with Magnets
SECTION 2 - CHALLENGERS OF THE UNKNOWN
CHAPTER FIVE - Wave Functions All the Way Down
CHAPTER SIX - The Equation That Made the Future!
CHAPTER SEVEN - The Uncertainty Principle Made Easy
CHAPTER EIGHT - Why So Blue, Dr. Manhattan?
SECTION 3 - TALES OF THE ATOMIC KNIGHTS
CHAPTER NINE - Our Friend, the Atom
CHAPTER TEN - Radioactive Man
CHAPTER ELEVEN - Man of the Atom
SECTION 4 - WEIRD SCIENCE STORIES
CHAPTER TWELVE - Every Man for Himself
CHAPTER THIRTEEN - All for One and One for All
SECTION 5 - MODERN MECHANICS AND INVENTIONS
CHAPTER FOURTEEN - Quantum Invisible “Ink”
CHAPTER FIFTEEN - Death Rays and DVDs
CHAPTER SIXTEEN - The One-Way Door
CHAPTER SEVENTEEN - Big Changes Come in Small Packages
CHAPTER EIGHTEEN - Spintronics
CHAPTER NINETEEN - A Window on Inner Space
SECTION 6 - THE WORLD OF TOMORROW
CHAPTER TWENTY - Coming Attractions
CHAPTER TWENTY-ONE - Seriously, Where’s My Jet Pack?
AFTERWORD
Acknowledgements
NOTES
RECOMMENDED READING
INDEX
PHOTO CREDITS
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To Thomas, Laura, and David,
who truly make the future
Our citizens and our future citizens cannot share
properly in shaping the future unless we understand the
present, for the raw material of events to come is the
knowledge of the present and what we make it.
LIEUTENANT GENERAL LESLIE R. GROVES
(WHO OVERSAW CONSTRUCTION OF THE PENTAGON AND WAS
CHIEF MILITARY LEADER OF THE MANHATTAN PROJECT)
FROM THE FOREWORD TO Learn How Dagwood Splits the Atom
WRITTEN BY JOHN DUNNING AND LOUIS HEIL AND DRAWN BY JOE MUSIAL
(KING FEATURES SYNDICATE, 1949)
INTRODUCTION
Quantum Physics? You’re Soaking in It!
Perhaps you share my frustration that, well into the twenty-first century, we still await flying cars, jet packs, domed underwater cities, and robot personal assistants. From the 1930s on, science fiction pulp magazines and comic books promised us that by the year 2000 we would be living in a gleaming utopia where the everyday drudgery of menial tasks and the tyranny of gravity would be overcome. Comparing these predictions from more than fifty years ago to the reality of today, one might conclude that, well, we’ve been lied to.
And yet . . . and yet. In 2010 we are able to communicate with those on the other side of the globe, instantly and wirelessly. We have more computing power in our laptops than in the room-size computers that were envisioned in the science fiction pulps. We can peer inside a person, without the slice of a knife, performing medical diagnoses using magnetic resonance imaging. Touch-activated computer screens, from the local ATM to the iPhone, are everywhere. And the number of automated devices we deal with in a given day is surprisingly high—though none of them look like Robby the Robot.
What did the all those rosy predictions miss? Simply put, they expected a revolution in energy, but what we got was a revolution in information. Implicit in the promise of jet packs and death rays is the availability of lightweight power supplies capable of storing large amounts of energy. But the ability of batteries to act as reservoirs of electrical energy is limited by the chemical and electrical properties of atoms. Scientists and engineers are extremely clever in developing novel energy-storage systems, but ultimately we can’t change the nature of the atoms. Information, however, requires only a medium to preserve ideas and intelligence to interpret them.
Moreover, information can endure for thousands of years—consider the long-term data storage accomplished by the Sumerians, whose cuneiform writing on clay tablets enables us to learn about their accounting systems and read the epic tale of Gilgamesh from four thousand years ago. These dried clay tablets, currently held in modern-day Iraq, are fairly bulky, and to share information from them the ancient Sumerians had to transport the actual tablets. But today you don’t have to go to Iraq to read the Sumerian tablets—you can view them on the Internet, or someone could send images of them to you instantly via a cell phone camera.
These advances in content storage and transmission were made possible by the development of semiconductor devices, such as the transistor and the diode. Back when the science fiction pulp magazines were first published, data manipulation proceeded via bulky vacuum tubes; the first computers employed thousands of such tubes, along with relay switches consisting of glass tubes filled with liquid mercury. The replacement of these tubes and mercury switche
s with semiconductor devices enabled an exponential increase in computing power accompanied by a similar decrease in the size of the computer. In 1965 Gordon Moore noted that approximately every two years the number of transistors that could be incorporated onto an integrated circuit doubled. This trend has held up for the past forty years and underlies the technological innovations that define our modern life: from book-size radios in the 1950s to an MP3 player no larger than a stick of gum in 2005; from a cell phone the size of a brick in the 1970s to one smaller than a deck of cards today. These advances in miniaturization have come with continued improvements in the ability to preserve and manipulate information. (If energy storage also obeyed Moore’s law, experiencing a doubling in capacity every two years, then a battery that could hold its charge for only a single hour in 1970 would, in 2010, last for more than a century.)
With no transistors, computers would still require bulky vacuum tubes, each one generating a significant amount of heat as it regulated electrical currents. A modest laptop computer currently employs approximately more than a hundred million solid-state transistors for data storage and processing. If all of these transistors were replaced with vacuum tubes, each one a few inches long and at least an inch wide, their physical dimensions, and the need to space them apart to avoid overheating, would yield a vacuum tube computer larger than the White House. Obviously, few institutions aside from the federal government and the largest corporations could afford such a massive computing device. We would consequently live in a relatively computer-free world. With computers rare, there would be no need to link them together, and no need to develop the World Wide Web. Commerce, journalism, entertainment, and politics would exist under the same constraints they did in the 1930s. If we’d had a revolution in energy storage (like the pulps predicted) rather than information storage, we could zip to work with jet packs, but once we got there we’d find no cell phones, no DVD or personal video recorders, no laser printers, and no personal computers.
The field of solid-state physics, which enabled the development of these and other practical devices, is in turn made possible through quantum mechanics. While science fiction writers were imagining what the future would look like, scientists at industrial laboratories and research universities were busy using the new understanding of the quantum world to create the transistor and the laser. These basic devices form the foundation of our modern lifestyle and have transformed not just consumer electronics, but chemistry, biology, and medicine as well. All of our lives would be profoundly different if not for the efforts in the first quarter of the twentieth century of a handful of physicists trying to understand how atoms interact with light. These pioneers of quantum mechanics recognized that they were changing the face of physics, but they almost certainly did not anticipate that they would also change the future.
In this book I will explain the key concepts underlying quantum mechanics and show how these ideas account for the properties of metals, insulators, and semiconductors, the study of which forms the field of solid-state physics. I’ll describe how the magnetic properties of atomic nuclei and atoms, an intrinsically quantum mechanical phenomena, allow us to see inside the human body using magnetic resonance imaging and store vast libraries of information on computer hard drives. The wonders enabled by quantum mechanics are almost too many to name: devices such as lasers, light-emitting diodes, and key-chain memory sticks; strange phenomena including superconductivity and Bose-Einstein condensation; and even brighter brights and whiter whites!1 And we’ll see how the same quantum phenomena that changed the very nature of technology in the last fifty years will similarly influence the growing field of nanotechnology in the next fifty years.
For a field of physics that has spawned applications that have had such a wide-ranging impact on our lives, it is unfortunate that quantum mechanics has such a reputation for “weirdness” and incomprehensibility. OK, maybe it is weird, but it’s certainly not impossible to understand. While the mathematics required to perform calculations in quantum physics is fairly sophisticated, its central principles can be described and understood without resorting to differential equations or matrix algebra.
The cover of the book promised a “math-free” discussion, but I must confess that there will be a little bit of math involved in this presentation of quantum physics. (I hope you are reading this at home and not standing up in the aisle at the bookstore, trying to decide whether or not to purchase this book.) Compared to the rigorous mathematics that underlies the foundations of quantum mechanics, the simple equations employed here practically qualify as “math-free.” I will make use of algebraic equations no more complex than those relating distance traveled to speed and time. That is, if I told you that I drove at a speed of 50 miles per hour for 2 hours, you would know that I had traveled 100 miles. By arriving at that conclusion, you have intuitively used the simple equation distance = speed × time. None of the math that I will use here will be more complicated than this.
While it may not be incomprehensible, quantum mechanics does have a well-deserved reputation for being confusing. I do not mean that the mathematics employed in a quantum description of nature is obscure or complex—all math is hard if you do not know how to use it, just as every language is opaque if you cannot speak it. Rather, I mean that fundamental questions, such as what happens to a quantum system when a measurement of its properties is performed, are still being argued over by physicists, nearly eighty years after first being posed. One of the most amazing aspects of quantum mechanics is that one can use it correctly and productively—even if one is confused by it.
In this book I invoke a “working man’s” view of quantum mechanics that has the advantage of requiring only three suspensions of disbelief, not unlike the “miracle exception from the laws of nature” that science fiction stories or superhero comic books often implicitly employ. Some of my professorial colleagues should note—in the interest of clarity I will sidestep some of the finer points of the theory. This book is intended for non-experts interested in learning how quantum mechanics underlies many of the devices that characterize our modern lifestyle. Meditations on the interpretations of quantum theory and the “measurement problem” are fascinating, to be sure, but philosophical discussions alone do not invent the transistor.
Even keeping it simple, questions regarding the fundamental nature of matter are inescapable when considering quantum mechanics. I discuss fantastical situations such as when two electrons or atoms are so close to each other that they become “entangled” and it is actually impossible to tell them apart. I encourage you to put fear out of your mind and not shirk any necessary heavy lifting, and I’ll try to hold up my end by using easily understood analogies and examples.
There are many excellent books that describe the historical development of quantum mechanics, some of which are listed in the “Recommended Reading” section. As I am not a historian of science, I will not retrace the steps of the pioneering physicists that led the quantum revolution, but will rather focus on explicating the physical principles they discovered and their applications in solid-state physics.
SECTION 1
TALES TO ASTONISH
Figure 1: Cover of the August 1928 issue of the science fiction pulp magazine Amazing Stories, which featured the debut of “Buck” Rogers.
CHAPTER ONE
Quantum Mechanics in Three Easy Steps
The future began twice: in December 1900, and in August 1928. On the first date, at the German Physical Society, Max Planck presented a resolution to something that would come to be called the ultraviolet catastrophe. Planck suggested that atoms can lose energy only in discrete jumps, and this new idea would tip over the first domino in a chain that by the mid-1920s would lead to the development of a new field of physics termed “quantum mechanics.” On the later date, at the end of the summer of 1928, Buck Rogers first appeared in the science fiction pulp Amazing Stories.
With its premier issue published in 1926, Amazing Stories was the first maga
zine devoted exclusively to science fiction stories, or what publisher Hugo Gernsback called “scientifiction.” The magazine’s motto was “Extravagant Fiction Today . . . Cold Fact Tomorrow.” Planck’s breakthrough marked the dawn of a new field of science and is the province of nerds, while the appearance of Buck Rogers began the future as reckoned by geeks. (I should note that as a physics professor who is also an avid fan of science fiction and comic books, I am simultaneously a nerd and a geek.)2
Given the amazing pace of scientific progress at the end of the nineteenth century—the invention of the telegraph, telephone, and automobile had radically altered notions of distance and time, such that, not for the last time, technology had made the world a somewhat smaller place—it is perhaps not surprising that readers of Amazing Stories in 1928 would expect the eventual development of personal flying harnesses and disintegrator rays.
Buck Rogers’s first adventure was described in Philip Francis Nowlan’s novella Armageddon 2419 A.D., published in that famous issue of Amazing Stories. Anthony Rogers—he would not gain the nickname “Buck” until his appearance in a syndicated newspaper comic strip one year later—was a citizen of both the twentieth and twenty-fifth centuries. Exposure to a gas leak in an abandoned mine near Scranton induced a former army air corps officer to lapse into a form of suspended animation. Upon awakening in the future, he rapidly adjusted to the new age. Nowlan’s hero, catapulted into the future, was just as resourceful as Twain’s Yankee thrust back into King Arthur’s court.
Rogers, armed with the weaponry of tomorrow and a military acumen acquired during his service in World War I, joins a team of rebels fighting against the evil “Hans” invaders from Asia who had conquered America in the early twenty-second century. In fact, many of the stories published in the science fiction pulps of the 1930s and 1940s are distinguished by optimism that in the future there would be continued scientific progress coupled with pessimism that there would be absolutely no improvement whatsoever in international (or interplanetary) relations.
The Amazing Story of Quantum Mechanics Page 1