Exactly: How Precision Engineers Created the Modern World. Simon Winchester

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      One last definition needs to be added to this mass of confusion: the concept of tolerance. Tolerance is an especially important concept here for reasons both philosophical and organizational, the latter because it forms the simple organizing principle of this book. Because an ever-increasing desire for ever-higher precision seems to be a leitmotif of modern society, I have arranged the chapters that follow in ascending order of tolerance, with low tolerances of 0.1 and 0.01 starting the story and the absurdly, near-impossibly high tolerances to which some scientists work today—claims of measurements of differences of as little as 0.000 000 000 000 000 000 000 000 000 01 grams, 10 to the -28th grams, have recently been made, for example—toward the end.^*

      Yet this principle also prompts a more general philosophical question: why? Why the need for such tolerances? Does a race for the ever-increasing precision suggested by these measurements actually offer any real benefit to human society? Is there perhaps a risk that we are somehow fetishizing precision, making things to ever-more-extraordinary tolerances simply because we can, or because we believe we should be able to? These are questions for later, but they nonetheless prompt a need here to define tolerance, so that we know as much about this singular aspect of precision as about precision itself.

      Although I have mentioned that one may be precise in the way one uses language, or accurate in the painting of a picture, most of this book will examine these properties as far as they apply to manufactured objects, and in most cases to objects that are manufactured by the machining of hard substances: metal, glass, ceramics, and so forth. Not wood, though. For while it can be tempting to look at an exquisite piece of wooden furniture or temple architecture and to admire the accuracy of the planing and the precision of the joints, the concepts of precision and accuracy can never be strictly applied to objects made of wood—because wood is flexible; it swells and contracts in unpredictable ways; it can never be truly of a fixed dimension because by its very nature it is a substance still fixed in the natural world. Whether planed or jointed, lapped or milled, or varnished to a brilliant luster, it is fundamentally inherently imprecise.

      A piece of highly machined metal, however, or a lens of polished glass, an edge of fired ceramic—these can be made with true and lasting precision, and if the manufacturing process is impeccable, they can be made time and time again, each one the same, each one potentially interchangeable for any other.

      Any piece of manufactured metal (or glass or ceramic) must have chemical and physical properties: it must have mass, density, a coefficient of expansion, a degree of hardness, specific heat, and so on. It must also have dimensions: length, height, and width. It must possess geometric characteristics: it must have measurable degrees of straightness, of flatness, of circularity, cylindricity, perpendicularity, symmetry, parallelism, and position—among a mesmerizing host of other qualities even more arcane and obscure.

      And for all these dimensions and geometries, the piece of machined metal must have a degree of what has come to be known^* as tolerance. It has to have a tolerance of some degree if it is to fit in some way in a machine, whether that machine is a clock, a ballpoint pen, a jet engine, a telescope, or a guidance system for a torpedo. There is precious little point in tolerance if the machined object is simply to stand upright and alone in the middle of a desert. But to fit with another equally finely machined piece of metal, the piece in question must have an agreed or stated amount of permissible variation in its dimensions or geometry that will allow it to fit. That allowable variation is the tolerance, and the more precise the manufactured piece, the greater the tolerance that will be needed and specified.

      A shoe, for instance, is invariably a thing of very low tolerance: on the one hand, a poorly made slipper may have “an agreed or stated amount of allowable variation in its dimensions” (which is the engineer’s formal definition of tolerance) of half an inch, with so generous an amount of wiggle room between foot and lining as to make the notion of precision almost irrelevant. A handmade brogue shoe by Lobb of London, on the other hand (or foot), may seem to fit snugly, perfectly, precisely even, but it will still have a tolerance of maybe an eighth of an inch—and in a shoe, such a tolerance would be acceptable, and the shoe indeed worn with pride. Yet, in terms of precision engineering, it is anything but precisely made; nor is it even accurately so.^*

      ONE OF THE two most precise measuring instruments ever built by human agency stands in America’s Pacific Northwest, far away from everything, in the arid middle of Washington State. It was built just outside the top-secret nuclear installation where the United States created the first supplies of plutonium for the bomb that destroyed Nagasaki, for decades the material at the heart of much of the nation’s arsenal of atomic weapons.

      The years of nuclear activity there have left an unimaginably large legacy of dangerously irradiated substances, from old fuel rods to contaminated items of clothing, which are only now, and after a loud public outcry, being remedied—or remediated, the term environmentalists prefer. Today, the Hanford site, as it is known, is officially the largest environmental cleanup site in the world, with decontamination bills reaching the tens of billions of dollars and the necessary remedial work likely to last until the middle of the twenty-first century.

      I first passed by the site very late one night, after a long drive from Seattle. From my southbound speeding car, I could see the glimmer of lights in the far distance. Behind razor-wire security fences and warning signs and under the protection of armed guards, some eleven thousand workers are now laboring night and day to cleanse the earth and waters of the poisonous radioactivity that so dangerously suffuses it. Some suppose it is a task so vast that it may never be properly completed.

      To the south of the main cleanup site, just outside the razor-wire fence but within sight of the still-standing towers of the remaining atomic piles, one of present-day science’s most remarkable experiments is being conducted. It is not secret at all, is unlikely to leave a legacy of any danger whatsoever, and requires the making and employment of an array of the most precise machines and instruments that humankind has ever attempted to construct.

      It is an unassuming place, easily missed. I arrived for my appointment in morning daylight, weary after the long nighttime drive. It was cold; the road was quite empty, the main turnoff unmarked. A small notice on the left pointed to a cluster of low white buildings a hundred yards off the road. “LIGO,” the sign read. “WELCOME.” And that was about all. Welcome to the current cathedral, it might also have said, to the worship of ultraprecision.

      It has taken decades to design the scientific instruments that are secreted out in the middle of this dust-dry nowhere. “We maintain our security by our obscurity” is the motto for those who fret about the costly experiments sited there, all without a fragment of barbed wire or chain link to protect them. The tolerances of the machines at the LIGO site are almost unimaginably huge, and the consequent precision of its components is of a level and nature neither known nor achieved anywhere else on Earth.

      LIGO is an observatory, the Laser Interferometer Gravitational-Wave Observatory. The purpose of this extraordinarily sensitive, complex, and costly piece of equipment is to try to detect the passage through the fabric of space-time of those brief disruptions and distortions and ripples known as gravitational waves, phenomena that in 1916 Albert Einstein predicted, as part of his general theory of relativity, should occur.

      If Einstein was right, then once every so often, when huge events occur far out in deep space (the collision of a pair of black holes, for instance), the spreading fan of interstellar ripples, all moving at the speed of light, should eventually hit and pass through the Earth and, in doing so, cause the entire planet to change shape, by an infinitesimal amount and for just the briefest moment СКАЧАТЬ