The National Institute of Standards and Technology, or NIST, oversees just about anything measurable in the United States. It collects and calibrates samples of materials. It owns the world’s tiniest ruler. It also standardizes the units by which we measure, which means everything from the meter (distance) to the mole (substance). But it’s the second (time) that has always fascinated Tom Vanderbilt, so off he went to discover — and, by extension, to delight us with — everything he could about that slippery duration.

In this world of metrology, which has left behind the dusty archives of physical things in favor of fundamental properties of the universe, it seems a kind of cosmic joke that this intangible, evanescent unit is the one that is understood most accurately. Even so, there is something amiss in the world of the second, the world of time. In a world of staggering exactitude, there are new timepieces on the horizon, capable of even more accuracy, clocks that are moving beyond mere measurement and opening new inquiries into time, into the universe itself. These machines have helped to drive a creeping suspicion that the second—that fundamental base unit upon which our temporal kingdom is built—despite all the synchronous activity of the world, despite the advent of clocks whose fidelity could theoretically outlast human civilization itself, is not being realized as exactly as it could be. Having come in search of the origin of time, I was learning that the very thing that drives it—the standard second—is flawed.