The rest of the contingent from Twilo listen to this theory and, weak as the empirical evidence is, after much arguing, they conclude that the youngster has a point. An elder statesman in the group—a physicist, it turns out—observes that a few rare events are sometimes more illuminating than a thousand mundane events. But the real clincher is the simple fact that there must be a ball. Posit the existence of a ball, which for some reason the Twiloans cannot see, and suddenly everything works. The game makes sense. Not only that, but all the theories, charts, and diagrams compiled over the past afternoon remain valid. The ball simply gives meaning to the rules.
This is an extended metaphor for many puzzles in physics, and it is especially relevant to particle physics. We can't understand the rules (the laws of nature) without knowing the objects (the ball) and, without a belief in a logical set of laws, we would never deduce the existence of all the particles.
THE PYRAMID OF SCIENCE
We're talking about science and physics here, so before we proceed, let's define some terms. What is a physicist? And where does this job description fit in the grand scheme of science?
A discernible hierarchy exists, though it is not a hierarchy of social value or even of intellectual prowess. Frederick Turner, a University of Texas humanist, put it more eloquently. There exists, he said, a science pyramid. The base of the pyramid is mathematics, not because math is more abstract or more groovy, but because mathematics does not rest upon or need any of the other disciplines, whereas physics, the next layer of the pyramid, relies on mathematics. Above physics sits chemistry, which requires the discipline of physics; in this admittedly simplistic separation, physics is not concerned with the laws of chemistry. For example, chemists are concerned with how atoms combine to form molecules and how molecules behave when in close proximity. The forces between atoms are complex, but ultimately they have to do with the law of attraction and repulsion of electrically charged particles—in other words, physics. Then comes biology, which rests on an understanding of both chemistry and physics. The upper tiers of the pyramid become increasingly blurred and less definable: as we reach physiology, medicine, psychology, the pristine hierarchy becomes confused. At the interfaces are the hyphenated or compound subjects: mathematical physics, physical chemistry, biophysics. I have to squeeze astronomy into physics, of course, and I don't know what to do with geophysics or, for that matter, neurophysiology.
The pyramid may be disrespectfully summed up by an old saying: the physicists defer only to the mathematicians, and the mathematicians defer only to God (though you may be hard pressed to find a mathematician that modest).
EXPERIMENTERS AND THEORISTS: FARMERS, PIGS, AND TRUFFLES
Within the discipline of particle physics there are theorists and experimenters. I am of the latter persuasion. Physics in general progresses because of the interplay of these two divisions. In the eternal love-hate relation between theory and experiment, there is a kind of scorekeeping. How many important experimental discoveries were predicted by theory? How many were complete surprises? For example, the positive electron (positron) was anticipated by theory, as were the pion, the antiproton, and the neutrino. The muon, tau lepton, and upsilon were surprises. A more thorough study indicates rough equality in this silly debate. But who's counting?
Experiment means observing and measuring. It involves the construction of special conditions under which observations and measurements are most fruitful. The ancient Greeks and modern astronomers share a common problem. They did not, and do not, manipulate the objects they are observing. The early Greeks either could not or would not; they were satisfied to merely observe. The astronomers would dearly love to bash two suns together—or better, two galaxies—but they have yet to develop this capability, and must be content with improving the quality of their observations. But in España we have 1,003 ways of studying the properties of our particles.
Using accelerators, we can design experiments to search for the existence of new particles. We can organize particles to impinge on atomic nuclei, and read the details of the subsequent deflections the way Mycenaean scholars read Linear B—if we crack the code. We produce particles; then we "watch" them to see how long they live.
A new particle is predicted when a synthesis of existing data by a perceptive theorist seems to demand its existence. More often than not, it doesn't exist, and that particular theory suffers. Whether it succumbs or not depends on the resilience of the theorist. The point is that both kinds of experiments are carried out: those designed to test a theory and those designed to explore a new domain. Of course, it is often much more fun to disprove a theory. As Thomas Huxley wrote, "The great tragedy of science—the slaying of a beautiful hypothesis by an ugly fact." Good theories explain what is already known and predict the results of new experiments. The interaction of theory and experiment is one of the joys of particle physics.
Of the prominent experimentalists in history, some—including Galileo, Kirchhoff, Faraday, Ampere, Hertz, the Thomsons (both J. J. and G. P.), and Rutherford—were fairly competent theorists as well. The experimenter-theorist is a vanishing breed. In our time Enrico Fermi was an outstanding exception. 1.1. Rabi expressed his concern about the widening gap by commenting that European experimentalists could not add a column of figures, and theorists couldn't tie their own shoelaces. Today we have two groups of physicists both with the common aim of understanding the universe but with a large difference in cultural outlook, skills, and work habits. Theorists tend to come in late to work, attend grueling symposiums on Greek islands or Swiss mountaintops, take real vacations, and are at home to take out the garbage much more frequently. They tend to worry about insomnia. One theorist, it is said, went to the lab physician with great concern: "Doctor, you have to help me! I sleep well all night, and the mornings aren't bad, but all afternoon I toss and turn." This behavior gives rise to the unfair characterization of The Leisure of the Theory Class as a takeoff on Thorstein Veblen's bestseller.
Experimenters don't come in late—they never went home. During an intense period of lab work, the outside world vanishes and the obsession is total. Sleep is when you can curl up on the accelerator floor for an hour. A theoretical physicist can spend his entire lifetime missing the intellectual challenge of experimental work, experiencing none of the thrills and dangers—the overhead crane with its ten-ton load, the flashing skull and crossbones and DANGER, RADIOACTIVITY signs. A theorist's only real hazard is stabbing himself with a pencil while attacking a bug that crawls out of his calculations. My attitude toward theorists is a blend of envy and fear but also respect and affection. Theorists write all the popular books on science: Heinz Pagels, Frank Wilczek, Stephen Hawking, Richard Feynman, et al. And why not? They have all that spare time. Theorists tend to be arrogant. During my reign at Fermilab I solemnly cautioned our theory group against arrogance. At least one of them took me seriously. I'll never forget the prayer I overheard emanating from his office: "Dear Lord, forgive me the sin of arrogance, and Lord, by arrogance I mean the following..."
Theorists, like many other scientists, can be fiercely, sometimes absurdly, competitive. But some theorists are serene, way above the battles that mere mortals engage in. Enrico Fermi is a classic example. At least outwardly, the great Italian physicist never even hinted that competition was a relevant concept. Whereas the common physicist might say, "We did it first!" Fermi only wanted to know the details. However, at a beach near Brookhaven Laboratory on Long Island one summer day, I showed him how one can sculpt realistic structures in the moist sand. He immediately insisted that we compete to see who would make the best reclining nude. (I decline to reveal the results of that competition here. It depends on whether you're partial to the Mediterranean or the Pelham Bay school of nude sculpting.)
Once, at a conference, I found myself on the lunch line next to Fermi. Awed to be in the presence of the great man, I asked him what his opinion was of the evidence we had just listened to, for a particle named the K-zero-two. He s
tared at me for a while, then said, "Young man, if I could remember the names of these particles I would have been a botanist." This story has been told by many physicists, but the impressionable young researcher was me.
Theorists can be warm, enthusiastic human beings with whom experimentalists (mere plumbers and electricians we) love to converse and learn. It has been my good fortune to enjoy long conversations with some of the outstanding theorists of our times: the late Richard Feynman, his Cal Tech colleague Murray Gell-Mann, the arch Texan Steven Weinberg, and my rival comic Shelly Glashow. James Bjorken, Martinus Veltman, Mary Gaillard, and T. D. Lee are other great ones who have been fun to be with, to learn from, and to tweak. A significant fraction of my experiments emerged from the papers of, and discussions with, these savants. Some theorists are much less enjoyable, their brilliance marred by a curious insecurity, reminiscent perhaps of Salieri's view of the young Mozart in the movie Amadeus: "Why, Lord, did you encapsulate so transcendent a composer in the body of an asshole?"
Theorists tend to peak at an early age; the creative juices tend to gush very early and start drying up past the age of fifteen—or so it seems. They need to know just enough; when they're young they haven't accumulated useless intellectual baggage.
Of course, theorists tend to receive an undue share of the credit for discoveries. The sequence of theorist, experimenter, and discovery has occasionally been compared to the sequence of farmer, pig, truffle. The farmer leads the pig to an area where there might be truffles. The pig searches diligently for the truffles. Finally, he locates one, and just as he is about to devour it, the farmer snatches it away.
GUYS WHO STAYED UP LATE
In the following chapters I approach the history and future of matter as seen through the eyes of discoverers, stressing—not, I hope, out of proportion—the experimenters. Think of Galileo, schlepping up to the top of the Leaning Tower of Pisa and dropping two unequal weights onto a wooden stage so he could listen for two impacts or one. Think of Fermi and his colleagues establishing the first sustained chain reaction beneath the football stadium of the University of Chicago.
When I talk about the pain and hardship of a scientist's life, I'm speaking of more than existential angst. Galileo's work was condemned by the Church; Madame Curie paid with her life, a victim of leukemia wrought by radiation poisoning. Too many of us develop cataracts. None of us gets enough sleep. Most of what we know about the universe we know thanks to a lot of guys (and ladies) who stayed up late at night.
The story of the a-tom, of course, includes theorists. They help us through what Steven Weinberg calls "the dark times between experimental breakthroughs," leading us, as he says, "almost imperceptibly to changes in previous beliefs." Weinberg's book The First Three Mittutes was one of the best, though now dated, popular accounts of the birth of the universe. (I always thought the book sold so well because people thought it was a sex manual.) My emphasis will be on the crucial measurements we have made in the atom. But you cannot talk about data without touching on theory. What do all these measurements mean?
UH-OH, MATH
We're going to have to talk a bit about math. Even experimenters cannot make it through life without some equations and numbers. To avoid mathematics entirely would be like playing the role of an anthropologist who avoids examining the language of the culture that is being studied, or like a Shakespearean scholar who hasn't learned English. Mathematics is such an intricate part of the weave of science—especially physics—that to dismiss it is to leave out much of the beauty, much of the aptness of expression, much of the ritualistic costuming of the subject. On a practical level, math makes it easier to explain how ideas developed, how devices work, how the whole thing is woven together. You find a number here; you find the same number there—maybe they're related.
But take heart. I'm not going to do calculations. And there won't be any math on the final. In a course I taught for nonscience majors at the University of Chicago (called "Quantum Mechanics for Poets"), I straddled the issue by pointing at the mathematics and talking about it without actually doing it, God forbid, in front of the whole class. Even so, I find that abstract symbols on the blackboard automatically stimulate the organ that secretes eye-glaze juice. If, for instance, I write x = vt (read: ex equals vee times tee), a gasp arises in the lecture hall. It isn't that these brilliant children of parents paying $20,000 tuition per year cannot deal with x = vt. Give them numbers for x and t and ask them to solve for v, and 48 percent would get it right, 15 percent would refuse to answer on advice of counsel, and 5 percent would vote present. (Yes, I know that doesn't add up to 100. But I'm an experimenter not a theorist. Besides, dumb mistakes give my class confidence.) What freaks out the students is that they know I'm going to talk about it. Talking about math is new to them and brings about extreme anxiety.
To regain my students' respect and affection I immediately switch to a more familiar and comfortable subject. Examine the following:
Think of a Martian staring at this diagram, trying to understand it. Tears spray out of his belly button. But your average high-school-dropout football fan yelps, "That's the Washington Redskins' goal-line 'Blast'!" Is this representation of a fullback off-tackle run that much simpler than x = vt? Actually, it's just as abstract, and certainly more arcane. The equation x = vt works anywhere in the universe. The Redskins' short-yardage play might score a touchdown in Detroit or Buffalo, but never against the Bears.
So think of equations as having a real-world meaning, just as diagrams of football plays—overcomplicated and inelegant as they are—have a real-world meaning on the gridiron. In fact, it's not all that important to manipulate the equation x = vt. It's more important to be able to read it, to understand it as a statement about the universe in which we live. To understand x = vt. is to have power. You will be able to predict the future and to read the past. It is both the Ouija board and the Rosetta Stone. So what does it mean?
The x tells where the thing is. The thing can be Harry cruising along the interstate in his Porsche or an electron zipping out of an accelerator. When x = 16 units, for example, we mean that Harry or the electron is located 16 units away from a place we call zero. The v is how fast Harry or the electron is moving—such as Harry tooling along at 80 mph or the electron dawdling at 1 million meters per second. The t represents the time elapsed after someone yells "go." Now we can predict where the thing will be at any time, whether t = 3 seconds or 16 hours or 100,000 years. We can also tell where the thing was, whether t = −7 seconds (7 seconds before t = 0) or t = −1 million years. In other words, if Harry starts out from your driveway and drives due east for one hour at a speed of 80 mph, then obviously he will be 80 miles east of your driveway an hour from "go." In reverse, you can also calculate where Harry was an hour ago (−1 hour), assuming his velocity was always v and that v is known—a critical assumption, because if Harry is a lush, he may have stopped at Joe's Bar an hour ago.
Richard Feynman presents the subtlety of the equation another way. In his version a cop stops a woman in a station wagon, sidles up to her window, and snarls, "Did you know you were going eighty miles an hour?"
"Don't be ridiculous," the woman replies. "I only left the house fifteen minutes ago." Feynman, thinking he had invented a humorous entrée to differential calculus, was shocked when he was accused of being a sexist for telling this story, so I won't tell it here.
The point of our little excursion into the land of math is that equations have solutions, and these solutions can be compared to the "real world" of measurement and observation. If the outcome of this confrontation is succcessful, one's confidence in the original law is increased. We'll see from time to time that the solutions do not always agree with observation and measurement, in which case, after due checking and rechecking, the "law" from which the solution emerged is relegated to the dustbin of history. Occasionally the solutions to the equations expressing a law of nature are completely unexpected and bizarre, and therefore bring the theory under s
uspicion. If subsequent observations show that it was right after all, we rejoice. Whatever the outcome, we know that the overarching truths about the universe as well as the functioning of a resonant electronic circuit or the vibrations of a structural steel beam are all expressed in the language of mathematics.
THE UNIVERSE IS ONLY SECONDS OLD (1018 OF THEM)
One more thing about numbers. Our subject often switches from the world of the very tiny to the world of the enormous. Thus we will be dealing with numbers that are often very, very large or very, very small. So, for the most part, I shall write them using scientific notation. For instance, instead of writing one million as 1,000,000,1 write it like this: 106. That means 10 raised to the sixth power which is a 1 followed by six zeroes, which is the approximate cost, in dollars, of running the U.S. government for about 20 seconds. Big numbers that don't conveniently start with a 1 can also be written in scientific notation. For instance, 5,500,000 is written 5.5 × 106. With tiny numbers, we just insert a minus sign. One millionth (1/1,000,000) is written like this: 10−6, which means a 1 that is six places to the right of a decimal point, or .000001.
What's important is to grasp the scale of these numbers. One of the disadvantages of scientific notation is that it hides the true immensity of numbers (or their smallness). The span of scientifically relevant times is mind-boggling: 10−1 seconds is an eye blink; 10−6 seconds is the lifetime of the muon particle, and 10−23 seconds is the time it takes a photon, a particle of light, to cross the nucleus. Keep in mind that going up by powers of ten escalates the stakes tremendously. Thus 107 seconds is equal to a bit more than four months, and 109 seconds is thirty years. But 1018 seconds is roughly the age of the universe, the amount of time that has transpired since the Big Bang. Physicists measure it in seconds—just a lot of them.
The God Particle: If the Universe Is the Answer, What Is the Question? Page 3
