Universe on a T-Shirt: The Quest for the Theory of Everything
Copyright © 2002, 2011 by Dan Falk
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For my parents
Contents
Acknowledgments
Note to the Reader
Introduction
Shadows and Light: The Greek World and the beginning of Science
A New Vision: The Copernican Revolution
Heaven and Earth: Galileo, Newton, and the Birth of Modern Science
Flashes of Insight: Electricity, Magnetism, and Light
Relativity, Space, and Time: Einstein’s Revolution
Quantum Theory and Modern Physics: Things Get Even Weirder
Tying Up Loose Ends: String Theory to the Rescue?
What Does It All Mean?:Science, God, and the Limits of Understanding
Epilogue
Recommended Reading
Endnotes
Credits
Acknowledgments
I’ve always been interested in astronomy, physics, and the universe, but my passion for string theory blossomed after attending two conferences in Chicago in December 1996. One was held in memory of the indian-born astrophysicist Subrahmanyan Chandrasekhar, and drew such luminaries as Stephen Hawking and Edward Witten. The other was the Texas Symposium on Relativistic Astrophysics, which, despite its name, is not always held in Texas. Since then I’ve become a bit of a science-conference junkie, attending symposiums and workshops across North America and becoming something of a “regular” at meetings of the American Astronomical Society and the American Physical Society. Stephen Maran, who handles media inquiries lor the AAS, and Phil Schcwe, who does the same for the APS, have given me numerous tips and contacts and answered hundreds of questions over the years.
My first major investigation of the themes in this book was carried out in 1997, when I put together a documentary called “From Empedocles to Einstein” for the CBC Radio program Ideas. That show was produced by Richard Handler, who helped focus many of my ideas. From that point onward, I had thought about writing a book’—but the plan only crystallized after I got an e-mail from Jennifer MacTaggart of Penguin Canada. Susan Folkins later helped steer me—and the book—in the right direction. I am also indebted to Rosemary Tanner for her tireless and invaluable help in editing the final manuscript, and to Joel Gladstone for his production editorial skills.
Dozens of scientists and historians answered countless questions and, in some cases, agreed to look over portions of the manuscript; particularly helpful were the physicists Pekka Sinervo, Amanda Peet, Glenn Slarkman, lohn Schwarz, and Michael Duff. Lengthy interviews with Edward Witten, Leon Lederman, Paul Davies, and John Barrow, which formed the heart oí my Ideas documentary, also bring life to these chapters. On the humanities side, I benefited greatly from discussions with John Traill, Alexander jones, James Robert Brown, and Dennis Richard Danielson. Owen Gingerich, an astronomer and historian of science, patiently granted interviews and responded to my numerous e-mail queries, while science writer Marcus Chown generously read several chapters. No doubt some errors remain; they are, of course, purely my responsibility.
Readers’ comments are welcome and can be sent to
universefeedback@hotmail.com.
Note to the Reader
Although I’ve tried to keep this book non-technical, there are occasions when distances, times, and other measurements come up. I have used metric units for distances, but those who are more familiar with Imperial units shouldn’t be put off. A kilometer is a bit more than half a mile; a centimeter is a bit less than half an inch, and a millimeter is one-tenth of a centimeter.
In astronomy and cosmology, much larger distances arise and we must switch to “light-years.” One light-year—the distance light travels in one year—is about 9500 billion kilometers or about 6000 billion miles.
Occasionally, we will also encounter very large or very small numbers. With large numbers, one can pile on strings of zeroes or refer to so many “billion billions”—but this soon becomes rather cumbersome; with small numbers (“billionths of billionths”), things become even uglier. The graceful solution, adopted by scientists everywhere, is to use scientific notation. Using this system, any number can be expressed as a “power of ten.” With large numbers, an “exponent” stands for the number of zeroes. For example:
one hundred = 100 = 102
ten thousand = 10,000 = 104
one billion = 1,000,000,000 = 109
and so on. With small numbers, the exponent becomes negative:
one hundredth = 1/100 = 10–2
one ten-thousandth = 1/10,000 = 10–4
one billionth = 1/1,000,000,000 = 10–9
Introduction
My ambition is to live to see all of physics reduced to a
formula so elegant and simple that it will fit easily on the
front of a T-shirt.
LEON LEDERMAN
The longed-for Theory of Everything promises to provide
the final discovery after which all physics will become the
refinement of its content, the simplification of
its explanation….
Eventually, it will appear on T-shirts.
JOHN D. BARROW
The universe explained. Not a long-winded, highly technical explanation, but one that is concise, simple, and elegant. The “Theory of Everything” will explain the physical world we see around us—people and planets, cars and comets, sand and stars. It will explain the origin of everything in our universe, and describe its most basic components. And while it will likely be expressed through abstract mathematics, the ideas at the heart of the theory may turn out to be extremely simple—so simple, in fact, that the essence of the theory can be written on a T-shirt. This remarkable goal, suggested by the quotes on the preceding page from leading physicists on both sides of the Atlantic, sounds like a fantasy, something dreamed up after the Friday afternoon bull session moved from the faculty lounge to the local pub. Yet it is not a proposition made on a him. It is a bold but very logical idea—a natural extension of what every physicist docs every day. What they’ve been doing, in fact, since the dawn of science.
In the chapters to come, we’ll explore this quest for simplicity in detail, tracing its evolution from ancient times, through the Scientific Revolution, to the provocative ideas of modern cosmology and particle physics. Let’s start, however, not with history or with physics, but with a riddle. You’re looking at a house across the street. You see a doctor enter, then a lawyer, and finally a priest. What is happeni
ng in that home? Before reading any further, take a moment to see if you can solve the riddle.
You probably figured out that the occupant of the house is terminally ill. First comes the doctor, who makes the diagnosis; then the lawyer, to settle the estate; and finally the priest, to administer last rites. What’s so appealing about that solution, of course, is that it’s so simple, so incredibly logical.
The situation described in the riddle is highly artificial, of course, but thousands of similar puzzles come along every day, confronting the scientist and non-scientist alike. Some are difficult; some are more straightforward. Suppose you walk into your living room and find one of the windows broken. Shards of glass lie on the carpet below the window. Nearby, a lamp is knocked over. Then, you see the crucial clue: a baseball, lying on the floor near the toppled lamp. The clues point overwhelmingly to one solution: someone must have hit a baseball through your window. Of course, you could come up with other explanations: maybe a burglar tried to get in through the window but gave up; meanwhile, the dog knocked over the lamp and dropped a baseball that he found in the yard. You don’t have to be a scientist, though, to recognize that one solution is far more likely than the other.
When the answers are obvious, the problems seem trivial; when the answers are less obvious, the problems can take years or even centuries to solve. Even before modern science had developed, philosophers were thinking about the best ways to approach such problems. They realized that the simple, elegant solution was usually right, A medieval English monk named William of Ockham expressed this idea so succinctly that his name is now attached to the concept. The argument has become known as “Ockham’s Razor.”
Ockham’s Razor is one of the most important “logical tools” that a scientist uses. Confronted with a bewildering array of data, the scientist looks for the simplest explanation for the observed facts. This is especially true in physics. The goal of the physicist has always been to simplify—to take a myriad of observations and explain them with as few laws and equations as possible. Physics is not philosophy, however, and the scientist has to take matters a few steps farther. Ockham’s Razor is a useful guideline, but it’s just the starting point. Every scientific theory must ultimately be tested by experiment. The theory has to predict specific results, and scientists have to perform laboratory tests to see if those results are obtained. A theory that doesn’t agree with observational evidence—although a few die-hards may cling to it—will eventually be discarded. That approach, often labeled the scientific method, has yielded spectacular successes over the last 400 years, from the work of Galileo and Newton to the great revolutions of relativity and quantum theory in the twentieth century. It continues to enrich our view of the universe today.
This Hubble Space Telescope photo reveals galaxies more than 10 billion light-years away. In the photo on the facing page, a magnetic field bends the paths of charged subatomic particles into distinct spirals. A successful Theory of Everything will apply to both realms, solving problems of the very large lin cosmology! and the very small (in particle physics).
In some branches of modern physics, however, experimental testing can be difficult—sometimes nearly impossible. Two fields are particularly challenging: high-energy particle physics, the search for nature’s ultimate building blocks, and cosmology, the study of the origin and evolution of the universe itself. The two disciplines, which at first might seem unrelated, are in fact intimately linked. Particle physicists explore how matter and energy behave under extreme conditions, usually by smashing particles into one another in giant accelerators. Equally extreme conditions prevailed in the early universe, the realm studied by cosmologists.
In the first split second after the big bang—the colossal explosion that gave birth to our universe some 15 billion years ago—the cosmos was so hot and dense that the various forces seen in nature today are thought to have acted as one. At that early time there was just a single force, a force which could be described by a single theory. Particle physicists and cosmologists are both struggling to understand that theory—the Theory of Everything.
Today, a great deal of excitement is focused on “string theory,” which describes all the known particles and forces in terms of tiny loops of string. It’s not as crazy as it sounds. With certain modifications, string theory may turn out to be our best hope for a unified theory of physics. Of course, we have no way to re-create the energy levels of the big bang in the laboratory; even today’s largest particle accelerators cannot come close. In other words, we have no direct way of testing siring theory. Where, then, does the theorist turn? One possibility is to test certain parts of the theory, to see if it’s “on the right track,” by checking for consistency with other, more strongly established theories. Another strategy is to heed the advice of Ockham and look for simplicity. These days, the science may seem esoteric and the equations complex—but the underlying ideas are often startlingly simple, even beautiful.
Driven by the search for concise, elegant explanations, physicists pursue theories that explain the widest range of physical phenomena. If possible, they test those theories in the laboratory; if not, they test them on the blackboard and on the computer. Often, they succeed. Each great revolution in the physical sciences, from Galileo and Newton to Maxwell and Einstein, has resulted in a new, simplified view of the universe; each has yielded an elegant description that can be expressed in a few simple equations.
In telling this story, I will also try to keep things simple. There will be no talk of “non-Abelian gauge theories,” “renormalization,” or “nonperturbative methods.” Of course, we will still have to stay alert—we’ll take an introductory tour of relativity and quantum mechanics, and we’ll explore the world of strings, black holes, and hidden dimensions. But we’ll never go any deeper than necessary to tie each discussion to our theme of simplicity and unification. And, though we’ll occasionally talk about math, we won’t actually do any math.
To truly understand this quest, however, we also need a sense of its history. We need to explore its origins, and its gradual evolution, beginning in the days when philosophy and science were one and the same. This book is a history of ideas, but it is also a story about people. Some were passionate experimenters, some were brilliant theoreticians, and a few were just plain lucky. But all were drawn by the quest for simplicity. All of them reached out for the holy grail of physics-—the Theory of Everything.
Shadows and Light
The Greek World and the
Beginning of Science
Zeus, father of the Olympians, has made night out of midday, hiding the bright sunlight, and…fear has come upon mankind.
ARCHILOCIIUS, SEVENTH CENTURY B.C.
By mid-afternoon, the shepherds knew something was wrong. The sheep and goats were bleating and the birds were crowing as if it were evening—but it was still only late afternoon. Sunset was two hours away, yet the light was fading and the air was cooling. The light was also changing color, mimicking the orange of twilight before turning an eerie silvery-gray. And, though it sounds impossible, the shadows were becoming weaker and yet more crisp at the same time. The sun was disappearing.
The day was the 28th of May. By our calendar, the year was 585 B.C.; for the Greek settlers in the province of Ionia, in Asia Minor, it was the fourth year of the 48th Olympiad. In the towns along the coast oí the Aegean Sea (today, part of Turkey), thousands of people stopped what they were doing to gaze at the spectacle unfolding in the sky. Though most of them did not know what was happening, some of the elders, and those who had traveled or had heard stories, understood that this was an eklipsis—an eclipse. It was, to be precise, a solar eclipse—the mid-day darkness that comes when the moon passes directly between the sun and the earth.
The eclipse also darkened the plains to the east, near the River Halys, where a great battle was raging. The Lydians, who lived just inland from the Greeks, were confronting the invading Medes, whose homeland was south of the Caspian Sea. We know about the
battle from the writings of Europe’s first historian, the Greek scholar Herodotus, who lived in the fifth century B.C. He tells us that the war had been waged for five years already, “during which both the Lydians and the Medes won a number of victories.” He says that “after five years of indecisive warfare, a battle took place in which the armies had already engaged when day was suddenly turned into night”—a reference, historians agree, to the eclipse of 585 B.C.. The two warring parties, viewing the eclipse as a sign of the displeasure of their gods—or perhaps simply seeing that an endless series of indecisive battles was doomed to bankrupt both empires—stopped fighting and quickly negotiated a peace treaty. The two leaders took an oath, Herodotus tells us, which was similar to that of the Greeks “but for additional confirmation they make a shallow cut in their arms and lick each other’s blood.”
The eclipse clearly caught the warring Lydians and Medes— and most of the Greeks—off guard. But a man named Thales (pronounced THAY-leez) was not so surprised. Herodotus tells us: “This change from daylight to darkness had been foretold to the Ionians by Thales of Miletus, who fixed the date for it in the year in which it did, in fact, take place.”
The account given by Herodotus is, of course, open to scholarly debate. But if we take it at face value, then the eclipse of 585 B.C. marks a turning point in the story of human civilization. Rather than attributing the eclipse to the whims of the gods, Thales saw it as an event that happened for a logical reason, as the result of natural forces. Today’s philosophers call such a view “naturalistic”—explaining things in terms of natural, rather than divine, laws. They might label Thales a “materialist”—someone who seeks explanations in terms of material forces and causes. (I’ll try to avoid using the adjective “materialistic,” as it makes us think of yuppies accumulating DVDs and driving SUVs.) Thales not only recognized eclipses as recurring natural phenomena, he also knew enough about their nature to predict when they would occur. (Compare this view to the reaction of the poet Archilochus, cited in the epigram at the start of this chapter, Archilochus placed the responsibility for that earlier eclipse—probably that of 648 B.C.—squarely at the feet of Zeus.)