The seven measures of the world

In this book ‘The Seven Measures of The World’, an Italian experimental physicist Piero Martin 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 the author, “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 the author 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 the author 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?” author 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 author’s narrative, though it helps when he gets into the more arcane corners, such as the measurement of visible light. Still, it is good fun overall.