THE SEVEN MEASURES OF THE WORLD

An Italian experimental physicist looks at seven means of gauging where we are in the world, from the meter to the second.

Some measurements are movable, such as the length of the sunlit day at various times of year, and some are variable, such as the width of a hand or the length of a bolt of cloth. “Nature,” writes Martin, “obviously, works perfectly well even without measurements.” Human society, not so much, and developing standard systems of measurement carries a component of social justice, “a universal system, the same for everybody.” That was easier said than done, of course: Developing the systems of measurement of which Martin writes, including the liter and hectare, first required a decimal metric system, with the usual inexactitudes until, within recent memory, the meter was finally measured “based on universal physical constants,” an example of Einsteinian relativity in action—“a meter is defined…as the distance traveled by light in a fraction of a second equal to 1/299,792,458.” Similarly, as Martin writes, the second used to be 1/86,400th of a terrestrial day, a measure that did not account for changes in the rate of Earth’s rotation. The author’s account is scientifically rich but also lightly worn. He connects the development of accurate standards of temperature to beer-making, for example—and who would have known that James Prescott Joule, for whom a unit of temperature is named, was a brewer? “Are you ready for a big number? A really big number?” Martin writes teasingly of the mole, a measure of substance that connects it to mass, relativity in action once again. It doesn’t take much scientific background to follow Martin’s narrative, though it helps when he gets into the more arcane corners, such as the measurement of visible light. Still, it’s good fun overall.

Entertaining popular science and a literate tale of why things are as they are.