THE RUMBLES OF REVOLUTION
Quantum theory becomes a ready target for writers who declare it akin to some sort of religion or mysticism. Classical Newtonian physics is often portrayed as safe, logical, intuitive. Quantum theory, counterintuitive and spooky, comes along and "replaces" it. It's hard to understand. It's threatening. One solution—the solution in some of the books discussed above—is to think of quantum physics as a religion. Why not consider it a form of Hinduism (or Buddhism, etc.)? That way we can simply abandon logic altogether.
Another way is to think of quantum theory as, well, science. And don't be taken in by this idea of its "replacing" what went before. Science doesn't toss out centuries-old ideas willy-nilly—especially if those ideas have worked. It is worth a short digression here to explore how revolutions in physics come about.
New physics doesn't necessarily vanquish old physics. Revolutions in science tend to be executed conservatively and cost-effectively. They may have staggering philosophical consequences, and they may seem to abandon the conventional wisdom about how the world works. But what really happens is that the established dogma is extended to a new domain.
Take that old Greek Archimedes. In 100 B.C. he summarized the principles of statics and hydrostatics. Statics is the study of the stability of structures like ladders, bridges, and arches—usually things that man has devised to make himself more comfortable. Archimedes' work on hydrostatics had to do with liquids and what floats and what sinks, with what floats upright and what rolls over; principles of buoyancy, why you scream "Eureka!" in a bathtub, and so on. These issues and Archimedes' treatment of them are as valid today as they were two thousand years ago.
In 1600 Galileo examined the laws of statics and hydrostatics, but extended his measurements to moving objects, objects rolling down inclined planes, balls tossed from towers, weighted lute strings swinging back and forth in his father's workshop. Galileo's work included Archimedes' work but explained much more. Indeed, his work extended to the features of the lunar surface and the moons of Jupiter. Galileo did not vanquish Archimedes. He engulfed him. If we were to represent their work pictorially, it would look like this:
Newton reached far beyond Galileo. By adding causation he was able to examine the solar system and diurnal tides. Newton's synthesis included new measurements of the motion of planets and their moons. Nothing in the Newtonian revolution threw any doubt on the contributions of Galileo or Archimedes, but Newton's revolution extended the regions of the universe that are subject to this grand synthesis.
In the eighteenth and nineteenth centuries, scientists began to study a phenomenon that was outside normal human experience. It was called electricity. Except for the frightening occurrence of lightning flashes, electrical phenomena had to be contrived to be studied (just as some particles must be "manufactured" in our accelerators). Electricity was then as exotic as quarks are today. Slowly, currents and voltages, electrical and magnetic fields, were understood and even controlled. The laws of electricity and magnetism were extended and codified by James Maxwell. As Maxwell and then Heinrich Hertz and then Guglielmo Marconi and then Charles Steinmetz and many others put these ideas to use, the human environment changed. Electricity surrounds us, communications crackle in the air we breathe. But Maxwell's respect for all who went before was flawless.
There wasn't much out beyond Maxwell and Newton—or was there? Einstein focused his attention at the rim of the Newtonian universe. His conceptual ideas went very deep; aspects of Galilean and Newtonian assumptions troubled him and eventually drove him to bold new premises. However, the domain of his observations now included things that moved with extraordinary speeds. Such phenomena were irrelevant to observers of the pre-1900 era, but as humans examined atoms, devised nuclear instruments, and began to look at happenings in the earliest moments of the universe's existence, Einstein's observations became important.
Einstein's theory of gravity also went beyond Newton's to include the dynamics of the universe (Newton believed in a static universe) and its expansion from an initial cataclysmic happening. Yet when Einstein's equations are aimed at the Newtonian world, they give Newtonian results.
So now we had the whole schmeer, no? No! We had yet to look inside the atom, and when we did, we needed concepts far beyond Newton (and unacceptable to Einstein) that extended the world down to the atom, the nucleus, and, as far as we know, beyond. (Within?) We needed quantum physics. Still, nothing in the quantum revolution cashed in Archimedes, sold out Galileo, skewered Newton, or defiled Einstein's relativity. Rather, a new domain had been sighted, new phenomena encountered. Newton's science was found inadequate, and in the fullness of time a new synthesis was discovered.
Remember we said in Chapter 5 that the Schrodinger equation was created to deal with electrons and other particles, but when applied to baseballs and other large objects, it transforms itself in front of our eyes to Newton's F = ma, or thereabouts. Dirac's equation, the one that predicted antimatter, was a "refinement" of the Schrodinger equation, designed to deal with "fast" electrons, which move at a significant fraction of the speed of light. Yet when the Dirac equation is applied to slow-moving electrons, out pops ... the Schrodinger equation, but magically revised to include the spin of the electron. But discard Newton? No way.
If this march of progress sounds wonderfully efficient, it's worth pointing out that it generates a good deal of waste as well. As we open new areas to observation with our inventions and our unquenchable curiosity (and plenty of federal grants), the data usually stimulate a cornucopia of ideas, theories, and suggestions, most of which are wrong. In the contest for control of the frontier there is, in terms of concepts, only one winner. The losers vanish into the debris of history's footnotes.
How does a revolution happen? During any period of intellectual tranquility, such as occurred in the late nineteenth century, there is always a set of phenomena that are "not yet explained." The experimental scientists hope their observations will kill the reigning theory. Then a better theory will take its place and reputations will have been made. More often, either the measurements are wrong or a clever application of the current theory turns out to explain the data. But not always. Since there are always three possibilities—(1) wrong data, (2) old theory resilient, and (3) need new theory—experiment makes science a lively métier.
When a revolution does occur, it extends the domain of science, and it may also have a profound influence on our world view. An example: Newton created not only the universal law of gravitation but also a deterministic philosophy that caused theologians to place God in a new role. Newtonian rules established mathematical equations that determined the future of any system if the initial conditions were known. In contrast, quantum physics, applicable to the atomic world, softens the deterministic view, allowing individual atomic events the pleasures of uncertainty. In fact, developments indicate that even outside the subatomic world, the deterministic Newtonian order is really too idealized. The complexities that compose the macroscopic world are so prevalent that for many systems, the most insignificant change in the initial conditions produces huge changes in the outcome. Systems as simple as the flow of water down a hill or a pair of dangling pendulums will exhibit "chaotic" behavior. The science of nonlinear dynamics, or "chaos," tells us that the real world is not nearly as deterministic as was once thought.
Which doesn't mean that science and the Eastern religions have suddenly discovered a lot in common. Still, if the religious metaphors offered up by the authors of texts comparing the new physics to Eastern mysticism help you in some way to appreciate the modern revolutions in physics, then by all means use them. But metaphors are only metaphors. They are crude maps. And to borrow an old expression: we must never mistake the map for the territory. Physics is not religion. If it were, we'd have a much easier time raising money.
6. ACCELERATORS: THEY SMASH ATOMS, DON'T THEY?
SENATOR JOHN PA STORE: Is there anything connected with the hopes of this accelerato
r that in any way involves the security of this country?
ROBERT R. WILSON: No sir. I don't believe so.
PASTORE: Nothing at all?
WILSON: Nothing at all.
PASTORE: It has no value in that respect?
WILSON: It has only to do with the respect with which we regard one another the dignity of men, our love of culture. It has to do with, are we good painters, good sculptors, great poets? I mean all the things we really venerate and honor in our country and are patriotic about. It has nothing to do directly with defending our country except to make it worth defending.
We have a tradition at Fermilab. Every June 1, rain or shine, at 7 A.M., the staff is invited to jog the four miles around the main ring of the accelerator on the surface road, which doubles as a jogging path. We always run in the direction that the antiprotons accelerate. My last unofficial time around the ring was 38 minutes. The current director of Fermilab, my successor John Peoples, put up a sign his first summer in the job, inviting the staff to run on June 1 with "a younger, faster director." Swifter he was, but neither of us was fast enough to beat the antiprotons. They complete the circuit in about 22 millionths of a second, which means that each antiproton laps me about 100 million times.
The Fermilab staff continues to be humiliated by the antiprotons. We get even, though, because we get to design the experiments. We steer the antiprotons head-on into protons racing just as fast in the opposite direction. The process of getting particles to collide is the essence of this chapter.
Our discussion of accelerators will be a bit of a departure. We've been racing through century after century of scientific progress like a runaway truck. Let's slow down the pace. Here we'll talk not so much about discoveries or even physicists but about machines. Instruments have been inextricably tied to scientific progress, from Galileo's inclined plane to Rutherford's scintillation chamber. Now an instrument takes center stage. One cannot understand the physics of the past several decades without understanding the nature of the accelerator and its accompanying array of particle detectors, the dominant tools in the field for the past forty years. By understanding the accelerator, one also learns much of the physics, for this machine embodies many principles that physicists have labored centuries to perfect.
I sometimes think about the tower at Pisa as the first particle accelerator, a (nearly) vertical linear accelerator that Galileo used in his studies. However, the real story starts much later. The development of the accelerator stems from our desire to go down into the atom. Galileo aside, the history begins with Ernest Rutherford and his students, who became masters of the art of exploiting the alpha particle to explore the atom.
The alpha particle is a gift. When some naturally radioactive materials spontaneously disintegrate, they shoot out these heavy, energetic particles. An alpha particle typically has an energy of 5 million electron volts. An electron volt (eV) is the amount of energy a single electron would receive if it crossed from the case (negative) of a 1-volt flashlight battery to the battery's terminal (positive). By the time you finish the next couple of chapters, the electron volt will be as familiar as the inch, the calorie, or the megabyte. Here are four abbreviations you should know before we go on:
KeV: thousand electron volts (K for kilo)
MeV: million electron volts (M for mega)
GeV: billion electron volts (G for giga)
TeV: trillion electron volts (T for tera)
Beyond TeV we resort to powers-of-ten notation, 1012 eV being one TeV. Beyond 1014, our foreseen technology runs out, and we are in the domain of cosmic ray particles, which bombard the earth from outer space. The numbers of cosmic ray particles are small, but their energies go all the way up to 1021 eV.
In particle physics terms, 5 MeV isn't very much. Rutherford's alphas barely managed to break up the nucleus of a nitrogen atom in perhaps the first on-purpose nuclear collision. And only tantalizing hints of what was to be learned emerged from those collisions. Quantum theory tells us that the smaller the object being studied, the more energy you need—equivalent to sharpening the Democritan knife. To cut the nucleus effectively we need energies of many tens or even hundreds of MeV. The more the better.
IS GOD MAKING THIS UP AS SHE GOES ALONG?
A philosophical digression. As I will describe, particle scientists went along cheerfully building ever more powerful accelerators for all the reasons any of us sapiens does anything—curiosity, ego, power, greed, ambition ... Every so often, a group of us in quiet contemplation over a beer would speculate about whether God Herself knows what our next machine—for example, the 30 GeV "monster" that was nearing completion at Brookhaven in 1959—will produce. Are we just inventing puzzles for ourselves by achieving these new, unheard-of energies? Does God, in Her insecurity, look over the shoulder of Gell-Mann or Feynman or one of Her other favorite theorists to find out what to do at those huge energies? Does She call together a committee of resident angels—Reb Newton, Einstein, Maxwell—to suggest what 30 GeV should do? This point of view is occasionally encouraged by the jumpy nature of theoretical history—as if She is making it up as we go along. However, progress in astrophysics and cosmic ray research quickly assures us that this is just Friday-evening-before-the-sabbath nonsense. Our colleagues who look up tell us with assurance that the universe is very much concerned with 30 GeV, with 300 GeV, indeed with 3 billion GeV. Space is awash with particles of astronomical (ouch!) energies, and what is today a rare and exotic happening at an infinitesimal collision point on Long Island or Batavia or Tsukuba was, just after the birth of the universe, an ordinary, everyday, garden-variety happening.
And now back to the machines.
WHY SO MUCH ENERGY?
The most powerful accelerator today, Fermilab's Tevatron, produces collisions at about 2 TeV, or 400,000 times the energy created by Rutherford's alpha particle collisions. The yet-to-be-built Superconducting Super Collider is designed to operate at about 40 TeV.
Now 40 TeV sounds like a great deal of energy, and it is indeed when invested in a single collision of two particles. But we should put this into perspective. When we strike a match, we involve about 1021 atoms in the reaction, and each process releases about 10 eV, so the total energy is roughly 1022 eV, or about 10 billion TeV. At the Super Collider there will be 100 million collisions per second, each one releasing 40 TeV, for a total of 4 billion TeV—not too different from the energy released in lighting a match! But the key is that the energy is concentrated in a few particles rather than in the billions and billions and billions of particles contained in any speck of visible matter.
We can look at the entire accelerator complex—from the oil-fired power station through the electrical power lines to the lab where transformers ship the electrical energy to magnets and radio-frequency cavities—as a giant device for concentrating, with extremely low efficiency, the chemical energy of oil into a measly billion or so protons per second. If the macroscopic quantity of oil was heated so that each of the constituent atoms had 40 TeV, the temperature would be 4 × 1017 degrees, four hundred thousand trillion degrees on the Kelvin scale. The atoms would melt into their constituent quarks. Such was the state of the entire universe less than a millionth of a billionth of a second after creation.
So what do we do with all this energy? Quantum theory demands more and more powerful accelerators to study smaller and smaller things. Here's a table showing the approximate energy one needs to crack open various interesting structures:
ENERGY (approximate) SIZE OF STRUCTURE
0.1 eV Molecule, large atom, 10−8 meters
1.0 eV Atom, 10−9 m
1,000 eV Atomic core, 10−11 m
1 MeV Fat nucleus, 10−14 m
100 MeV Nuclear core, 10−15 m
1 GeV Neutron or proton, 10−16 m
10 GeV Quark effects, 10−17 m
100 GeV Quark effects, 10−18 m (more detail)
10 TeV God Particle? 10−20 m
Note how predictably the required energy goe
s up as the size goes down. Note also that you need only 1 eV to study atoms, but 10 billion eV to begin to study quarks.
Accelerators are like the microscopes used by biologists to study ever smaller things. Ordinary microscopes use light to illuminate the structure of, say, red corpuscles in blood. Electron microscopes, beloved by the microbe hunters, are more powerful precisely because the energy of the electrons is higher than that of the light in an optical microscope. The electrons' shorter wavelengths allow biologists to "see" the molecules from which a corpuscle is constructed. It is the wavelength of the bombarding object that determines the size of what you can "see" and study. In quantum theory we know that as the wavelength gets shorter the energy increases; our chart simply demonstrates the connection.
In 1927, Rutherford, in an address to Britain's Royal Society, expressed the hope that one day scientists would find a way to accelerate charged particles to energies higher than that provided by radioactive decay. He foresaw the invention of machines capable of generating many millions of volts. There was a motivation for such machines beyond pure power. Physicists needed to be able to hurl more projectiles at a given target. Alpha sources provided by nature were less than bountiful: fewer than a million particles could be directed toward a 1-square-centimeter target per second. A million sounds like a lot, but nuclei occupy only one hundredth of a millionth of the target area. You need at least a thousand times more accelerated particles (a billion) and, as mentioned, a lot more energy—many millions of volts (physicists weren't sure how many millions)—to probe the nucleus. This seemed like a daunting task in the late 1920s, yet physicists in many laboratories began to work on the problem. What ensued was a race to create machines that would accelerate the requisite huge number of particles to at least one million volts. Before we discuss the advances in the technology of accelerators, we should talk about some basics.
The God Particle Page 26
