Chad Orzel is one of my favorite explainers of scientific concepts, and in his new book A Brief History of Timekeeping, he covers one of my favorite topics: Time. But the story of time isn’t just about time itself, as you will see — it’s also about those who try to keep it.
If I ask you to think about time, odds are you picture a clock, a relatively recent technological invention. The oldest mechanical clocks show up around 1200 CE, and accurate pendulum clocks were only invented in the mid-1600s. Electronic clocks with digital readouts, like the ones on seemingly every modern appliance, are a 20th-century invention.
This might lead you to believe that our preoccupation with keeping track of time is a relatively recent development, maybe even one associated with the particular form of modern civilization. The argument of my new book is that this is wrong: timekeeping is a universal human obsession, with a history that stretches back thousands of years, to before written language.
The Big Idea here can be expressed in a very simple form, as an expansion of our definition of a “clock”: A clock is just a thing that ticks. It might be an audible tick, like the pendulum clock that hangs in our dining room, or it might be silent, like the vibration of the tiny quartz crystals that regulate all those digital clocks scattered around. It might be blindingly fast, like the 9,192,631,770 oscillations per second of the microwaves in a cesium atomic clock, or ponderously slow like the motion of the rising sun along the horizon as the seasons change.
All these things are clocks, and they all have a “tick”: a regular repeated action we can count to mark the passage of time. That idea of counting “ticks” is extremely ancient, and extremely powerful. Basically every human civilization that we know anything about has devoted significant effort to tracking and marking the passage of time.
The most ancient types of clocks use the motion of the sun: sundials are clocks that “tick” once a day, when the shadow of some object completes its sweep across the face. Solstice markers “tick” once a year, when the rising or setting sun returns to a particular point on the horizon picked out by massive stone structures. The passage tomb at Newgrange is more than five thousand years old, and still functions perfectly to mark the December solstice.
Manufactured devices to mark shorter intervals also date back thousands of years. The “tick” of a water clock is the filling or emptying of a container with a hole in it, and we have records of their use dating back to 1500 BCE. Water clocks were the state of the art in timekeeping up until the Renaissance, when the pendulum clock came along, marking time with the regular swings of a mass on a string. And with the development of quantum mechanics in the 20th century, physicists learned how to use the energy states of atoms to make perfect clocks with no physical moving parts, just light waves oscillating at a frequency determined by universal laws.
The story of timekeeping isn’t just about nuts-and-bolts technology, though: it’s a human story, and so involves human choices and drama. Different societies have developed timekeeping systems that reflect their particular priorities, a fact most dramatically demonstrated by the elaborate and mysterious calendrical system of the Maya. The implementation and standardization of time is also a political process, as shown by the delicate negotiations that led to the Gregorian calendar reform in 1582, or the implementation of time zones in the most American way possible in 1883.
A Brief History of Timekeeping covers all these topics, and more. In it, I explain the science underlying some of the most significant “ticks” in the history of timekeeping: the basic astronomy of the sun and moon, the physics of an oscillating pendulum, the quantum rules we use to define the second. I also talk about the cultures and the politics of time through the ages, with examples that span the globe and thousands of years. I even get into the connection between the intensely practical business of synchronizing clocks and the revolutionary shift in the philosophical understanding of time brought about by Einstein’s theory of relativity.
All of these topics return to the same big idea: a clock is a thing that ticks. And humans all over the world have spent the last several thousand years identifying ticks and making ever better clocks. I hope you’ll spend a little of your time to learn about those efforts.