From a Field of Metaphors, a Crop of Ideas May Sprout


An old friend wrote me recently from his new post at MIT, describing one of his colleagues as a typical "dot edu," and another as an uptight "dot com." For those of you not yet plugged into e-mail, the dot followed by the three letters designates the origin of your Internet address: edu for educational institutions, com for commercial enterprises, org for nonprofits and gov for you-know-who.

Inevitably, the jargon of the science invades the popular lexicon. We've grown accustomed to calling suggestions "input," and dismissing ideas that "don't compute." These days, if a physicist wants to send you something, he's likely to ask you to give him your "coordinates."

We tend to forget how much of our everyday speech descends from science. Timothy Leary's call to "turn on and tune in" wouldn't have made much sense before the taming of electricity. Nobody talked about taking "quantum leaps" (much less named a TV show after them) before the inner world of the atom revealed its quantum mechanical secrets. And no one was described as "irrational" before the discovery of irrational numbers.

Metaphors also flow the other way, from everyday life to science. Indeed, metaphors are scaffolding that holds science up while new theories are under construction.

Fields of magnetism are not like fields of daisies, but they help us visualize how influences can spread through space. Electrons do not flow through wires like water through faucets, but thinking of currents this way helps us to imagine them.

Eventually, the metaphor breaks down, the scaffolding cracks under the weight of new evidence. These cracks are good places to look for new physics.

Take the atom. Before its inner structure was understood, physicists described it as a miniature solar system--electrons orbiting like planets around a central nucleus. But they soon realized that atoms didn't behave like planetary systems in several important ways. For example, every carbon atom (or helium or iron atom) in the universe is exactly alike.

How do atoms remain forever the same, like some minuscule Dorian Gray, without the benefit of plastic surgery?

The trick is, they absorb or emit energy only in precisely measured parcels (the famous quantum leaps). The subatomic world is not like a solar system at all, but rather like a phonograph record, with electrons confined to orbiting in specific grooves. If the atom was jostled or torn apart, it could only come back together in one of those preset configurations.

Of course, the record metaphor is ultimately inadequate as well. It may help us visualize why atoms absorb energy in lumps, but it doesn't explain why they also change their "spin" in lumps. Indeed, it's hard to imagine how particles such as electrons "spin" at all, given that they are pointlike, with no dimension. As physicist Vera Kistiakovsky pointed out, "They have nothing to spin around." In the end, spin, as well, is only a metaphor.

Metaphors can be traps, and good scientists are always wary of them. At a recent gathering of physicists at UC Santa Barbara, physicist John Peoples talked about the challenges facing those who would understand the world of the very small, the inner world not only of atoms, but also of atomic building blocks, such as protons.

Physicists think the proton is composed of more fundamental particles called quarks. Until recently, the reigning metaphor had it that quarks lay inside the proton just as protons lay inside the nuclei of atoms--like a box inside another box.

But the recently discovered top quark is enormously more massive than a proton--which came as a complete surprise. Instead of opening a box and finding a smaller one, they looked inside the proton and found something far more massive than the proton itself. Defining exactly what a proton is, Peoples said, "is not a simple question."

To get to the next step, the physicists will have to find a new set of metaphors. But any attempt to talk about atoms in everyday terms is ultimately doomed. No one said it better than physicist Erwin Schroedinger, one of the founders of quantum mechanics.

"A complete satisfactory model of this type is not only practically inaccessible, but not even thinkable," he said. "Or, to be precise, we can, of course, think of it, but however we think it, it is wrong."

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