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cuits and machines of nanotechnology. They have joined with biologists: Perhaps in the not-too-distant future they will use optical tweezers to rearrange the genetic code. They have begun to explore radical new ideas of quantum computing. Physicists are to be found in NASA, in industries, and, increasingly, on Wall Street as techniques born in the study of physical systems begin to play an important role in examining the dynamics of stocks, bonds, options, and hedge funds. Physics is large in the vast national laboratories of Los Alamos, Oak Ridge, Fermilab, the Stanford Linear Accelerator Center (SLAC), and Brookhaven. Physics is small in the start-up optics company or in the bench-top experiments that are reconfiguring the study of new materials, optical phenomena, biophysics, and magnetic media.

Precisely because physics is everywhere, from computer printers, copying machines, and laser-driven checkout counters to precision weapons, surgical instruments, airplane surfaces, and medical diagnostics, it is a tall order to survey the whole of it. One way to cast a first glance over the landscape is to think of the different distance scales of nature.

A few years ago, Sebastian Junger wrote A Perfect Storm, a moving account of a few small boats caught in the harsh fall Atlantic during the extraordinarily violent storm of October 1991. We learn of the killer waves, some almost a hundred feet high and roughly that long, that threatened the lives of anyone so unfortunate as to be at sea. Any small craft would eventually lose the power to face into the waves and once caught sideways would almost certainly be thrown keel up and sunk. Even on a calm day, the complexities of the sea seem impossible to understand, especially on discovering that there are waves of every conceivable size, from a fraction of an inch to giant ocean surges that stretch for a thousand miles. But there is a simplification available, one that in some ways undergirds the entirety of physics. It is this: Not all the ups and downs of a boat at sea are equally threatening. Waves much shorter in length than a boat make little difference; those an inch or a foot or even a couple of feet long do no damage. Much longer waves can equally well be ignored. A surge measuring a thousand feet from crest to crest merely lifts the boat gradually up and settles it back down. But waves roughly as long as the boat are potentially destructive. This simple fact—that of the myriad of interdependent waves, only those of roughly boat length are directly threatening—lies close to the heart of physics.

Take the string theorists. These are a group of physicists with the wildly ambitious goal of bringing together the various matter-binding forces (weak, electromagnetic, strong) with gravity. Using (and occasionally inventing) new mathematics, string theory has fastened on the unimaginably small