Another layer off the Onion
Stanford, Calif. — If you think, as I did two weeks ago, that a "gluon" is a name tag, "heavy lepton" is a Jewish wrestler from Brooklyn, and that "quark hunting" is something Pooh and Piglet do in one of A. A. Milne's stories, then you're probably not ready to go to the head of the class. At least not a class in modern physics.
These "jabberwocky" terms are names given to recently discovered families of particles hundreds of millions times smaller than the atom -- which for a half century was thought to be the basic building block of nature. (To put this in perspective, the ink in the period at the end of this sentence contains roughly 4 billion atoms, one for every person on the face of the earth.)
These new particles are not only smaller than ever thought possible, but they challenge traditional thinking about the nature of matter, time, space, and casualty. Some of them appear to travel backward in time, to be in different places at the same time, to be simultaneously both particle and wave, and to have antimatter "partners," with which they can collide and disappear into pure energy.
High-energy, or particle, physics, is one of the most exciting and volatile fields in modern science. Its frontiers are being pushed back so rapidly that textbooks that were written on the subject five or more years ago are outdated. Just as astronomers build larger telescopes to see more distant stars, physicists are constructing more powerful machines to tear atoms apart and larger "microscopes" to probe the mysterious structure of the atom.
In the foothills behind Stanford University is a two-mile-long particle "gun" that has begun firing electrons near the speed of light into "microscopes" the size of airplane hangars. It is part of the Positron-Electron Project (PEP), just completed as a joint effort of the Standard Linear Accelerator Center (SLAC) and the University of California's Lawrence Berkeley Laboratory. PEP added what physicists call a "storage ring" to this "gun." Funded by the Department of Energy, it cost $78 million to build. Its 1.3-mile circumference makes PEP one of the largest and most powerful particle "microscopes" in the world; it is a leading contender in the race to find the "missing quark," an elusive clue in the puzzle of what may be the basic constituency of matter.
How PEP works is deceptively simple. Electrons and their antimatter particles, positrons, are boosted through the SLAC accelerator, which looks like a two-mile chain of tuna tins encased in a concrete tunnel large enough to drive a freight train through. At the end of the accelerator is a "switching yard" in which the particles are directed into PEP's ring and hurtled in opposite direction at velocities approaching 186,282 miles per second, the speed of light.
In the subsequent head-on collision of the beam of electrons and positrons, the particles are annihilated, producing pure energy. (Every time PEP is fired up, Einstein's special theory of relativity -- E mc and all that -- is proved.) Within a few millionths of a second, the unstable package of energy materializes into new particles, which scientists quickly record. The hope is that PEP has enough energy to knock loose the elusive sixth quark and help physicists learn more about quarks, leptons, gluons, and other new families of particles and forces that bind them.
Inside PEP each moving particle carries 18 billion electron-volts (GeV), and by the time they reach the end of the two-mile accelerator the particles are 50, 000 times heavier than when they were stationary. The composite energy of two particles of 18 GeV each crashing head-on is 36 GeV, the ultimate power of PEP. Before PEP and its smaller precursor, SPEAR (Stanford Positron Electron Asymmetric Ring), accelerated particles from the main SLAC machine were smashed into particles in stationary targets.
"In is like an elephant running over a mouse," says Sidney Drell, deputy director of SLAC. "The moving electron has 50,000 times the weight of the stationary one. So the mouse gets flattened and the elephant keeps running. What we wanted was a collision between an elephant and an anti-elephant. The best way to see what's inside an elephant is to crash two of them head-on and let them splatter. The electron and positron splatter into new forms of energy and that's what we are looking at."
Adapting zoological metaphors to the abstractions of high-energy physics is to be expected of Drell, SLAC's resident Renaissance man. The highly respected theoretical physicist is no closet scientist. In addition to his research, he has been a consultant on the subject to the White House, Congress, and the Pentagon. On his office bulletin board is a photograph of the detonation of the atom bomb over Hiroshima. Nearby is a picture of Andrei Sakharov, the Soviet physicist-turned-dissident who helped the Russians develop the hydrogen bomb and then spoke out against its use.
On the lower left corner of Drell's bulletin board is a photocopy of a hand-scribbled note Beverly Sills once sent him, asking him backstage after a San Francisco performance. Drell is an opera buff, and like Albert Einstein (whose bust is in Drell's office), he plays the violin.
"An interest in [classical] music is quite common among theoretical physicists and mathematicians," he says. "Perhaps we're listening for the music of the spheres, the harmony of the universe. I really don't know."
Drell is also reluctant to forecast the success of PEP and practical implications the new research might have.
"Whenever you open a new frontier, whenever you cross a new boundary, it's a question of whether you are running into a forest, a jungle, or a desert; you just don't know," he says. "PEP is simply studying nature with a higher resolving power. If you want to push forward the frontiers of what we're made of, you have to keep going to a smaller and smaller scale."
He and his associates are asking the same questions as the Greek metaphysician: What are we made of? What is the world made of?
The search to find the basic building blocks of matter dates back at least to the 5th century BC, when the Greek philosopher (philosophers were also the scientists of the day) Anaxagoras suggested that the structure of nature was "seeds within seeds, within seeds, in an unending progression, each as complex as the whole."
One of his contemporaries, Democritus, postulated, however, that there must be a final point at which matter got no smaller. In 460 BC he mentally halved a stick of wood, until he reached what he hypothetically thought was the absolute smallest unit of matter. He called it the "atom" (derived from the Greek word meaning "indivisible"). Said Democritus: "Aside from atoms and empty space, there are only opinions."
At the end of the 19th century J. J. Thompson, an English physicist, further unraveled the atom. In 1897 he discovered an even smaller particle he called an "electron."
Thompson consequently theorized that the atom must be a positively charged ball with negatively charged electrons embedded in it. That notion was soon dubbed the "plum pudding," or "raisins-in-the-bun," model. As delicious as Thompson's model looked, in 1911 the brilliant but irascible New Zealand physicist Ernest Rutherford said nuts to raisin buns. Nature, he claimed, was much more complicated. Rutherford suggested that the atom was mostly empty space and resembled a miniature solar system, with the negatively charged electrons orbiting a positive nucleus.
(Lord Rutherford, sometimes called the "father of atomic physics," repeatedly dismissed the idea that his work had any practical applications and as late as 1933 said that anyone looking for a new source of power in the atom's nucleus was "talking moonshine." The thought of nuclear power and atom bombs was beyond him.)
Like the proverbial blind men describing an elephant, scientists throughout this century have devised divergent theories of atomic structure. After Rutherford's nuclear atom came Niels Bohr's "impossible atom" and Erwin Schrodinger's wave-mechanical atom.
In the 1960s physicists detected a "graininess" to the neutrons and protons in the atom's nucleus. In 1964, a leading physicist at the California Institute of Technology, Murray Gell-Mann, suggested (concurrently with George Zweig) that the universe was built on an odd family of particles called "quarks." By definition, they were so tiny and so invisibly locked inside matter that they could never be detected. (The word "quark" was borrowed from James Joyce's "Ulysses," in which, like so many words invented by the Irish novelist, it has no apparent meaning.)
Since the scientists have discovered five "flavors" of quarks (up, down, strange, charm, and bottom), and the search is on for the antimatter companion of the fifth quark: a sixth, or "top" quark.
To complicate matters (not to mention matter), an American physicist, Sheldon Glashow, subsequently decided that quarks come in three "colors": red, yellow, and blue. (Like the word "quark," the terms "flavor" and "color" were chosen arbitrarily and have no connection to the meaning of the word.) In 1974, SLAC physicist Burton Richter and Samuel C. C. Ting at the Brookhaven National Laboratory simulateneously discovered something called the "j particle," or "psi particle," which, they claim, give experimental backing to the existence of quarks. (For that discovery Richter and Ting shared the Nobel Prize for Physics in 1976.)
Physicists believe that a sixth quark is hiding somewhere inside the atom; the search is on. Staford scientists have been "tunning up" PEP for the last several months and expect to begin experimental runs sometime in Kanuary.The West Germans already have a positron-electron machine called PETRA, which is slightly more powerful than PEP. They also had a year's head start on PEP, but so far the Germans' quick search for the sixth quark has been in vain, says Drell.
Some scientists believe that neither machine is powerful enough to knock loose what could be the final quark. At the moment the 12 European countries that support CERN, a nuclear research facility near Geneva, are considering building a positron-electron machine that would be 15 to 20 miles in circumstance. The cost of construction would be around $1 billion, and operation of the machine would demand as much electronic power as the entire city of Geneva.
Is there method or madness in carrying "quark hunting" to success extremes?
"We are looking for the ultimate building block," Drell says. "The prejudice of elementary-particle physicists is that there should be a small fraternity of particles out of which we can build the rest of the universe. We are looking for an exclusive 'social register' of fundamental particles.
"We now have such a variety of quarks, we give them funny names, color and flavor. There are growing families of what we call leptons, particles that do not partake of the strong nuclear forces. There is the elctron, there's heavy brother called the mu meson. And that was bad enough until Marty Perl at SLAC discovered a third one, which is 36,000 times as heavy as the electron, called the tau lepton.
"So now we have a proliferating family of the leptons . . . each associated with its own neutrino [a particle with no charge and little if any mass]. We have so many of the family of elementary particles that the 'social register' isn't very exclusive anymore. So we keep looking for something to unify at a lower level" -- an even lower common denominator.
Might there be a particle smaller than a quark? A number of physicists say no, on the basis of what they call the "quark confinement hypothesis." It basically states that because it is impossible either to produce or isolate a quark, it must therefore be impossible to break it down to smaller, more basic particles. Others hold to the "infinite onion" theory of the universe: Beneath each layer scientists will peel back yet another and another.
Says Drell: "At any stage the question is, is this the ultimate level or is there another structure within the one we're studying? Every time we unleash our imagination and make predictions, we've found that nature is richer than our imagination. Every time in the past when wise old men have said, 'Well, we've reached the end of the line, this is it, they're wrong."
In his primer on high-energy physics, called "Particles," physicist Michael Chester observes: "The world of particles is very strange, compared with the everyday world of our experience. It is strange to realize that these two worlds fit together -- that our everyday reality is somehow built out of particles such as protons, pions, and quarks, that are both particles and waves, things that might move backward and forward in time.
In peculiar behavior has led some physicists to speculate that particles may not exist in space or time. . . . In our perceptions we organized the things that we experience, arranging events so that we think of 12:00 as coming before 12:01. We think of one object as object as being next to another object. . . . Only in our thoughts and our dreams do we come close to being free of the limitations of space and time. . . . Perhaps it is our own limitations in having to arrange our perceptions in space and time that clouds the universe from our view. Certainly the physical universe is much more dreamlike and much less mechanical than we generally realize."
Drell repeats: "Physicists are in search of a sort of Holy Grail, with a faith that there is some elegant, simple, beautiful system in nature to be discovered. It's a form of religion, you might say."
Three years ago he wrote in Daedelus, the journal of the American Academy of Arts and Sciences, that modern physicists were moving closer to the description given in the Bible (Hebrews 11:3): "Through faith we understand that the worlds wer framed by the word of God, so that the worlds were framed by the word of God , so that things which are seen were not made of things which do appear."