The Scales of Judgment
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POSTERMINARIES
The Scales of Judgment Materials scientists are generally wellversed in physics, and physics, above all, is a science of measurements. The first instinct of a physicist is to parse a problem in terms of its measurables in the dimensions of mass, length, and time, and it is the shifting of attention down the scale of length that particularly characterizes our present times as the Nano Age. In materials laboratories, there has traditionally been an understanding that complete “quantitativity” is not always achievable, but it is better to have a qualitative assessment than none at all. This presents us with a challenge, because our training in physics endows us with a particular value system. If it can’t be measured, it’s not respectable, so we strive to make our qualitative assessments as quantitative as possible, or at least to seem that way. Long in the past, before the evolutionary lines of materials and geology separated, we could comfortably use comparative measurements like Moh’s scale of hardness, which places materials in order by determining which of them will scratch others. Once all of the materials are ranked, ranging from talc to diamond, an arbitrary numerical scale is imposed, assigning a number from 1 to 10 to each material in the list, and providing an illusion of quantitativity. After the great evolutionary divide, however, materials scientists have tended to assess “hardness” in terms of indentation tests rather than anything so arbitrary as scratching one rock against another. At first, indentation tests produced results in terms of standardized “hardness numbers” according to the scales provided by the manufacturers of the testing machines: Rockwell or Vickers. Later, with a wider range of micro- and nanoindenters becoming available, hardnesses began to be reported in numbers that have actual SI units. Clearly, materials science is evolving toward physics, while geology is still in a primitive state, characterized by the striking together of rocks. Just don’t get any ideas about hardness— even if it is measured in newtons per square meter—having any physical meaning. It is an example of illusory quantitativity. The number you get will still depend on how you do the test: doubling the load does not double the area of the indentation. Our many tools for chemical analysis have made us more comfortable with different kinds of analysis, including “qualitative,” “comparative,” and “quantitative.” Interestingly, some manufacturers impose a patina of quantitativity even on this scale, replacing its midpoint with “semi-quantitative”: literally, “half-quantitative.” I wonder how it was determined to be half-, and not, say, 65%-quantitative. Once when I asked a student to describe the nature of her analytical results, she wavered for a
moment and then said “Quanlitative!” Lewis Carroll would have been proud. A new example of what he called a portmanteau word: a merger of two equally appropriate (or inappropriate) terms to give an ideal compromise. Whatever terminology you use, the message i
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