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Undisciplined Science

Brian Hayes

Fishing Expeditions 

The lattice models constitute a set of problems and tools that span an impressive diversity of disciplines. But which of those disciplines is their true home? Who owns those models?

From one point of view, such a question doesn't even deserve an answer. The "intellectual property" of the pure sciences is still considered a public trust, freely available to anyone with the wit to use it. You don't have to be a licensed mathematician to write a differential equation. And unsolved problems are like fish in the sea—there for the taking by anyone who has the right bait and tackle. Nevertheless, academic communities get nervous when foreign fleets begin trawling in local waters. And no wonder. When you've been chasing the big fish all your life, it takes an uncommonly generous turn of mind to rejoice in watching someone else land it.

A scientific discipline—whether physics or mathematics or anthropology—is more than just a body of knowledge. It's also a community of people, together with the organizations and cultural traditions that bind them together—the journals they read, the meetings they attend, the jokes they tell. Such institutions resist change, and most of them are quite stable over the span of a human lifetime. But upheavals are not unknown. In retrospect these events may look exciting and rejuvenating, but some of the participants must have found them traumatic. Two historical examples worth pondering are the rise of astrophysics in the 19th century and the invention of molecular biology in the 20th.

Astronomy had its first close encounter with physics in the era of Kepler and Newton, but the consequences of that conjunction extended only to the limits of the solar system. Astronomy as applied to the stars remained the kind of science that Rutherford derided as stamp collecting. There wasn't much you could do with the stars but catalog them—give them names and note their positions, their brightness, and perhaps some hint of their color. Nothing was known of their mass and size, their composition, their age or the source of their radiant energy. The French philosopher August Comte cited the chemistry of the stars as an example of something that would remain forever unknowable.

Figure 3. The percolation of a fluid . . .Click to Enlarge Image

What overturned this pessimistic assessment was an infusion of new instruments and methods, most notably spectroscopy. The discovery that narrow lines observed in stellar spectra could be matched up with corresponding lines in the spectrum of a candle flame brought the stars right into the laboratory. Almost immediately, spectroscopists were identifying chemical elements in the stars (including, in the case of helium, an element that had not yet been found on Earth). Later, subtler features of the spectra allowed inferences about temperature and pressure in stellar atmospheres, and even the measurement of stellar magnetic fields. This new style of stellar science was thoroughly multidisciplinary. There were astronomers (John Herschel) but also chemists (Robert Bunsen), physicists (Gustav Kirchhoff) and even a polymath pioneer of photography (William Henry Fox Talbot). The instigator of the whole spectroscopic revolution was an optician (Joseph von Fraunhofer). The term astrophysics, coined by the German physicist J. K. F. Zölner, must have sounded odd at the outset—as sociophysics and econophysics do today—but it has entered the mainstream now. In most universities, the Department of Astronomy is now named Astronomy and Astrophysics.

In biology, the quest to understand the molecular basis of life also involved ideas and personnel recruited from other disciplines, and yet the story is a little different. The prominent role of physicists in this undertaking is often remarked. Of the four people most closely associated with the double-helix model of DNA—Francis Crick, Rosalind Franklin, James Watson and Maurice Wilkins—three began their careers in physics or physical chemistry. Another seminal figure was Max Delbrück, who studied quantum physics with Niels Bohr before turning to biology. At least one major technology was imported from physics: X-ray crystallography became a tool for mapping the structure of biomolecules. Although Delbrück and Crick brought no new instruments with them, perhaps they passed along a physicist's style of problem-solving. Delbrück set out to find the simplest possible biological system for investigating the mechanism of heredity—he chose the bacterial viruses called phages—much as a physicist would reduce a magnet to a lattice of spins. Still, however much molecular biology may have been influenced by the physicists who helped create it, the field remains a province of biology, not a colonial outpost of physics.

In describing events like these, the choice of a metaphor makes all the difference. When physicists turned their attention to genes and proteins, did they come as a plundering horde, descending on the defenseless villages of innocent biologists? Or were they refugees from the war-blasted landscape of physics, grateful for a new home in a more peaceable realm, and eager to earn their keep by helping with the chores? Or was it an alliance, a marriage of equals but opposites, demonstrating the benefits of hybrid vigor? It would doubtless make everyone feel better if we could adopt the last of these fables, but such symmetrical unions are rare. For one thing, some disciplines just have more to export, whereas others tend to run a trade deficit. Physics and mathematics are defined as much by their methods as by their subject matter, but in fields such as geology or entomology the tricks of the trade tend to be more specialized. 

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