The God Particle: If the Universe Is the Answer, What Is the Question?

by Leon Lederman

  BRAZILIAN DEBT, SHORT SKIRTS, AND VICE VERSA

  The third consequence of the experiment was that Schwartz, Steinberger and Lederman were awarded the Nobel Prize in physics, but not until 1988, some twenty-seven years after the research had been done. Somewhere I heard of a reporter interviewing the young son of a new laureate: "Would you like to win a Nobel Prize like your father?" "No!" said the young man. "No? Why not?" "I want to win it alone."

  The Prize. I do have some comments. The Nobel is awesome to most of us in the field, probably because of the luster of the recipients, starting with Roentgen (1901) and going through so many of our heroes including Rutherford, Einstein, Bohr and Heisenberg. The Prize gives a colleague who wins it a certain aura. Even when your best friend, one with whom you have peed together in the woods, wins the Prize it somehow changes him in your eyes.

  I had known that at various times I had been nominated. I suppose I could have received the Prize for the "long-lived neutral kaon," which I discovered in 1956, for this was quite an unusual object, used today as a tool for studies of crucial CP symmetry. I could have gotten it for the pion-muon parity research (with C. S. Wu), but Stockholm chose to honor the theoretical instigators instead. Actually, that was a reasonable decision. Still, the byproduct discovery of polarized muons and their asymmetric decay has had extensive applications to condensed matter and atomic and molecular physics, so much so that international conferences on this subject are held regularly.

  As the years passed, October was always a nervous month, and when the Nobel names were announced, I would often be called by one or another of my loving offspring with a "How come...?" In fact, there are many physicists—and I'm sure this is true of candidates in chemistry and medicine as well as in the nonsciences—who will not get the Prize but whose accomplishments are equivalent to those of the people who have been recognized. Why? I don't know. It's partly luck, circumstances, the will of Allah.

  But I have been lucky and have never lacked recognition. For doing what I love to do, I was promoted to full professor at Columbia in 1958 and paid reasonably well. (Being a professor in an American university is the best job in Western civilization. You can do anything you want to do, even teach!) My research was vigorous, aided by some fifty-two graduate students over the years 1956–1979 (at which time I became Fermilab director). Most of the time the rewards came when I was too busy to anticipate them: election to the National Academy of Science (1964), the President's Medal of Science (Lyndon Johnson gave it to me in 1965), and other assorted medals and citations. In 1983 Martin Perl and I shared the Wolf Prize, given by the state of Israel, for discovering the third generation of quarks and leptons (the b quark and the tau lepton). Honorary degrees also came in, but that's a seller's market, since hundreds of universities are each seeking four or five people to honor every year. With all that, one begins to acquire a modicum of security and a calm attitude toward the Nobel.

  When the announcement finally came, in the form of a 6 A.M. phone call on October 10, 1988, it released a hidden store of uncontrolled mirth. My wife, Ellen, and I, after very respectfully acknowledging the news, laughed hysterically until the phone starting ringing and our lives started changing. When a reporter from the New York Times asked me what I was going to do with the prize money, I told him I couldn't decide between buying a string of racehorses or a castle in Spain, a quote he duly printed. Sure enough, a real estate agent called me the next week, telling me about a great deal on a chateau in Castille.

  Winning the Nobel Prize when you are already reasonably prominent has interesting side effects. I was director of Fermilab, which has 2,200 employees, and the staff basked in the publicity, taking the occasion as a sort of early Christmas present. A lab-wide meeting had to be repeated several times so everyone could listen to the Boss, who was already pretty funny, but who was suddenly considered on a par with Johnny Carson (and was being taken seriously by really important people). The Chicago Sun-Times shook me up by headlining NOBEL STRIKES HOME, and the New York Times put a picture of me, sticking my tongue out, on the front page—above the crease!

  All of this fades, but what didn't fade was the public awe at the tide. At receptions all over the city I was introduced as the winner of the 1988 Nobel Peace Prize in physics. And when I wanted to do something rather spectacular perhaps foolhardy, to help the Chicago public schools, the Nobel holy water worked. People listened, doors opened, and suddenly we had a program for improving science education in inner-city schools. The Prize is an incredible ticket to help one effect socially redeeming activities. The other side of the coin is that no matter what you won the Prize for you become an instant expert in all things. Brazilian debt? Sure. Social Security? Yeah. "Tell me, Professor Lederman, what length will women's dresses be?" "As short as possible!" responds the laureate with lust in his heart. But what I do intend is to use the Prize shamelessly to help advance science education in the United States. For this task a second Prize would be helpful.

  The Strong Force

  The triumphs in working out the intricacies of the weak force were considerable. But there were still those hundreds of hadrons nagging us, a plethora of particles, all of which were subject to the strong force, the force that holds the nucleus together. The particles had a variety of properties: charge, mass, and spin are some we have mentioned.

  Pions, for example. There are three different pions closely spaced in mass, which, after being studied in a variety of collisions, were placed together in a family—the pion family, oddly enough. Their electric charges are plus one, minus one, and zero (neutral). All the hadrons, it turned out, came in family clusters. The kaons line up like this: . (The signs, +, −, and 0, indicate the electric charge. The bar atop the second neutral kaon indicates that it is an antiparticle. The sigma family portrait looks like this: Σ+, Σ0, Σ−. A more familiar group to you is the nucleon family: the neutron and proton, components of the atomic nucleus.

  The families consist of particles of similar mass and similar behavior in strong collisions. To express this idea more specifically, the term "isotopic spin," or isospin, was invented. Isospin is useful in that it allows us to look at the concept of "nucleon" as a single object coming in two isospin states: neutron or proton. Similarly "pion" comes in three isospin states: π+, π− π0. Another useful property of isospin is that in strong collisions it is a conserved quantity, like charge. A violent collision of a proton and an antiproton may produce forty-seven pions, eight baryons, and other stuff, but the total isotopic spin number remains constant.

  The point is that physicists were trying to make some sense out of these hadrons by sorting through as many properties as they could find. So there are lots of properties with whimsical names: strangeness number, baryon number hyperon number and so on. Why "number"? Because all these are quantum properties, hence quantum numbers. And quantum numbers obey conservation principles. This permitted theorists or out-of-experiment experimentalists to play with the hadrons, organize them, and, inspired perhaps by biologists, classify them into larger family structures. Theorists were guided by rules of mathematical symmetry, following the belief that the fundamental equations would respect such deep symmetries.

  One particularly successful organization was devised in 1961 by the Cal Tech theorist Murray Gell-Mann, who called his scheme the Eightfold Way, after the teaching of the Buddha: "This is the noble Eightfold Way: namely, right views, right intention, right speech..." Gell-Mann correlated hadrons almost magically into coherent groups of eight and ten particles. The allusion to Buddhism was yet another excursion into whimsy, so common in physics, but various mystics seized upon the name as proof that the true order of the world is related to Eastern mysticism.

  I got into trouble in the late 1970s, when I was asked to write a little biography of myself for the Fermilab newsletter on the occasion of the discovery of the bottom quark. Not expecting anyone other than my coworkers in Batavia to read the piece, I entitled the story "An Unauthorized Autobiography"
by Leon Lederman. To my horror the story was picked up and reprinted in the CERN newsletter and then in Science, the official journal of the American Association for the Advancement of Science, read by hundreds of thousands of scientists in the United States. The story included the following: "His [Lederman's] period of greatest creativity came in 1956 when he heard a lecture by Gell-Mann on the possible existence of neutral K mesons. He made two decisions: First, he hyphenated his name..."

  Anyway, by any other name, a theorist would smell as sweet, and Gell-Mann's Eightfold Way gave rise to charts of hadron particles that were reminiscent of the Mendeleev periodic table of the elements, though admittedly more arcane. Remember Mendeleev's chart with its columns of elements having similar chemical properties? This periodicity was a clue to the existence of an internal organization, to the shell structure of electrons, even before we knew about electrons. Something inside the atoms was repeating, making a pattern as the atoms increased in size. In retrospect, after the atom was understood, it should have been obvious.

  THE SCREAM OF THE QUARK

  The pattern of hadrons, arranged by assorted quantum numbers, also screamed for substructure. It isn't easy, however, to hear the screams of subnuclear entities. Two keen-eared physicists did, and wrote about it. Gell-Mann proposed the existence of what he referred to as mathematical structures. In 1964 he postulated that the patterns of organized hadrons could be explained if three "logical constructs" existed. He called these constructs "quarks." It is generally assumed that he lifted the word from James Joyce's diabolical novel Finnegans Wake ("Three quarks for Muster Mark!"). George Zweig, a colleague of Gell-Mann's, had an identical idea while working at CERN; he named his three things "aces."

  We will probably never know precisely how this seminal idea came about. I know one version because I was there—at Columbia University in 1963. Gell-Mann was giving a seminar on his Eightfold Way symmetry of hadrons when a Columbia theorist, Robert Serber, pointed out that one basis for the "eight" organization would involve three subunits. Gell-Mann agreed, but if these subunits were particles they would have the unheard-of property of having third-integral electric charges—⅓, ⅔, −⅓, and so on.

  In the particle world, all electric charges are measured in terms of the charge on the electron. All electrons have exactly 1.602193 × 10−19 coulombs. Never mind what coulombs are. Just know that we use the previous complicated figure as a unit of charge and call it 1 because it's the charge on the electron. Conveniently, the proton's charge is also 1.0000, as is that of the charged pion, the muon (here the precision is much higher), and so on. In nature, charges come in integers—0, 1, 2 ... All the integers are understood to be multiples of the number of coulombs given above. Charges also come in two styles: plus and minus. We don't know why. That's the way it is. One might imagine a world in which the electron could, in a bruising collision or in a poker game, lose 12 percent of its electric charge. Not in this world. The electron, proton, pi plus, et al. always have charges of 1.0000.

  So when Serber brought up the idea of particles with third-integral charges—forget it. Such things had never been seen, and the rather curious fact that all observed charges were equal to an integral multiple of a unique, unchanging standard charge became, over time, incorporated into the intuition of physicists. This "quantization" of electric charge was in fact used to seek some deeper symmetry that would account for it. However, Gell-Mann reconsidered and proposed the quark hypothesis, simultaneously blurring the issue, or so it seemed to some of us, by suggesting that quarks aren't real but are convenient mathematical constructs.

  The three quarks born in 1964 are today called "up," "down," and "strange," or u, d, and's. There are, of course, three antiquarks: and . The properties of the quarks had to be delicately chosen so that they could be used to build all of the known hadrons. The u quark is given a charge of +⅔ the d quark is -⅓ as is the's quark. The antiquarks have equal but opposite charges. Other quantum numbers are also selected so that they add up correctly. For example, the proton is made of three quarks—uud—with charges +⅔, +⅔, and -⅓, the sum being +1.0, which jibes with what we know about the proton. The neutron is a udd combination, with charges +⅔, -⅓, -⅓, for a sum of 0.0, which makes sense because the neutron is neutral, zero charge.

  All hadrons consist of quarks, sometimes three and sometimes two, according to the quark model. There are two classes of hadrons: baryons and mesons. Baryons, which are relatives of protons and neutrons, are three-quark jobs. Mesons, which include pions and kaons, consist of two quarks—but they must be a quark combined with an and quark. An example is the positive pion (π+), which is ud. The charge is +⅔ +⅓, which is equal to 1. (Note that the d-bar, the antidown quark, has a charge of +⅓.)

  In fashioning this early hypothesis, the quantum numbers of the quarks, and properties such as spin, charge, isospin, and so on, were fixed in order to account for just a few of the baryons (proton, neutron, lambda, and so on) and mesons. Then these numbers and other relevant combinations were found to fit all the hundreds of known hadrons. It all worked! And all the properties of a composite—for example, a proton—are subsumed by the properties of the constituent quarks, moderated by the fact that they are in intimate interaction with one another. At least, that is the idea and the task for generations of theorists and generations of computers, given, of course, that they are handed the data.

  Quark combinations raise an interesting question. It is a human trait to modify one's behavior in company. However; as we shall see, quarks are never alone, so their true unmodified properties can only be deduced from the variety of conditions under which we can observe them. In any case, here are some typical quark combinations and the hadrons they produce:

  BARYONS MESONS

  uud proton positive pion

  udd neutron dū negative pion

  uds lambda neutral pion

  uus sigma plus positive kaon

  dds sigma minus sū negative kaon

  uds sigma zero neutral kaon

  dss xi minus neutral antikaon

  uss xi zero

  Physicists gloried in the spectacular success of reducing hundreds of seemingly basic objects to composites of just three varieties of quarks. (The term "aces" faded—no one can compete with Gell-Mann when it comes to naming.) The test of a good theory is whether it can predict, and the quark hypothesis, guarded or not, was a brilliant success. For example, the combination of three strange quarks, sss, was not among the record of discovered particles, but that didn't stop us from giving it a name: omega minus (Ω−). Because particles containing the strange quark had established properties, the properties of a hadron with three strange quarks, sss, would also be predictable. The omega minus was a very strange particle with a spectacular signature. In 1964 it was discovered in a Brookhaven bubble chamber and was exactly what Dr. Gell-Mann had ordered.

  Not that all issues were settled—not by a long shot. Lots of questions: for starters, how do quarks stick together? This strong force would be the subject of thousands of theoretical and experimental papers over the next three decades. The jawbreaking title "quantum chromodynamics" would propose a new breed of messenger particles, gluons, to cement(!!) quarks together. All in due course.

  CONSERVATION LAWS

  In classical physics there are three great conservation laws: energy, linear momentum, and angular momentum. They have been shown to be deeply related to concepts of space and time, as we will see in Chapter 8. Quantum theory introduced a great number of additional quantities that are conserved; that is, they do not change during a variety of subnuclear, nuclear and atomic processes. Examples are electric charge, parity, and a host of new properties like isospin, strangeness, baryon number, and lepton number. We have already learned that the forces of nature differ in their respect for different conservation laws; for example, parity is respected by the strong and electromagnetic forces but not by the weak force.

  To test a conservation law, one examines a huge number of re
actions in which a particular property, say the electric charge, can be ascertained before and after the reaction. We recall that energy conservation and momentum conservation were so solidly established that when certain weak processes appeared to violate them, the neutrino was postulated as a saving mechanism, and it was right. Other clues to the existence of a conservation law have to do with the refusal of certain reactions to take place. For example, an electron does not decay with two neutrinos because that would violate charge conservation. Another example is proton decay. Recall that it doesn't. Protons are assigned a baryon number that is ultimately derived from its three-quark structure. So protons, neutrons, lambdas, sigmas, and so on—all three-quark fellows—have baryon number +1. The corresponding antiparticles have baryon number -1. All mesons, force carriers, and leptons have baryon number 0. If baryon number is strictly conserved, then the lightest baryon, the proton, can never decay, since all the lighter decay-product candidates have baryon number 0. Of course, a proton-antiproton collision has total baryon number 0 and can give rise to anything. So baryon number "explains" why the proton is stable. The neutron, decaying into a proton, an electron, and an antineutrino, and the proton inside the nucleus, which is able to decay into a neutron, a positron, and a neutrino, conserve baryon number.

  Pity the guy who lives forever. The proton can't decay into pions because it would violate baryon number conservation. It can't decay into a neutron and a positron and a neutrino because of energy conservation. It can't decay into neutrinos or photons because of charge conservation. There are more conservation laws, and we feel that the conservation laws shape the world. As should be obvious, if the proton could decay it would threaten our existence. Of course, that does depend on the proton's lifetime. Since the universe is fifteen or so billion years old, a lifetime much longer than this would not influence the fate of the Republic too much.