Why Time Flies: A Mostly Scientific Investigation - Softcover

Alan Burdick is a staff writer and former senior editor at The New Yorker and a frequent contributor to Elements, the magazine’s science-and-tech blog. His writing has also appeared in The New York Times Magazine, Harper’s, GQ, Discover, Best American Science and Nature Writing, and elsewhere. His first book, Out of Eden: An Odyssey of Ecological Invasion, was a National Book Award finalist and won the Overseas Press Club Award for environmental reporting. 

Why Time Flies
I settle into a seat on the Paris Métro and rub the sleep from my eyes. I feel unmoored. The calendar says late winter but outside my window the day is warm and fair, the leaf buds gleam, the city is resplendent. I arrived from New York yesterday and stayed out past midnight with friends; today my head is still in the dark, glued in a season and a time zone several hours behind me. I glance at my watch: 9:44 a.m. As usual, I am late.

The watch is a recent gift from my father-in-law, Jerry, who wore it himself for many years. When Susan and I became engaged, her parents offered to buy me a new watch. I declined, but for a long time afterward I couldn’t shake the worry that I’d made a poor impression. What sort of son-in-law ignores the time? So when Jerry subsequently offered me his old wristwatch I said yes right away. It has a golden dial set on a wide silver wristband; a black face bearing the brand name (Concord) and the word quartz in bold letters; and the hours denoted by unnumbered lines. I liked the new weight on my wrist, which made me feel important. I thanked him and remarked, more accurately than I could understand at that moment, that it would be a helpful addition to my research on time.

On the evidence of my senses, I had come to believe that the time “out there” in clocks, watches, and train schedules is quantifiably distinct from the time coursing through my cells, body, and mind. But the fact was that I knew as little about the former as I did about the latter. I could not say how a particular clock or watch worked nor how it managed to agree so closely with the other watches and clocks that I occasionally noticed. If there was a real difference between external and internal time—as real as the difference between physics and biology—I had no idea what it was.

So my new, used watch would be a kind of experiment. What better way to plumb my relationship to time than to physically attach it to me for a while? Almost immediately I saw results. For the first few hours of wearing the watch I could think about nothing else. It made my wrist sweat and tugged at my whole arm. Time dragged literally and, because my mind dwelt on the dragging, figuratively. Soon enough I forgot about the watch. But on the evening of the second day I suddenly remembered it again when, while bathing one of our infant sons in the tub, I noticed it on my wrist, underwater.

Secretly I hoped that the watch might confer some degree of punctuality. For instance, it seemed to me that if I looked at the watch often enough I might yet arrive on time for my ten o’clock appointment in Sèvres, just outside Paris, at the Bureau International des Poids et Mesures—the International Bureau of Weights and Measures. The Bureau is an organization of scientists devoted to perfecting, calibrating, and standardizing the basic units of measurement used around the world. As our economies globalize, it becomes ever more imperative that we all be on precisely the same metrological page: that one kilogram in Stockholm equals exactly one kilogram in Jakarta, that one meter in Bamako equals exactly one meter in Shanghai, that one second in New York equals exactly one second in Paris. The Bureau is the United Nations of units, the world standardizer of standards.

The organization was formed in 1875 through the Convention of the Metre, a treaty meant to ensure that the basic units of measurement are uniform and equivalent across national borders. (The first act of the Convention was for the Bureau to hand out rulers: thirty precisely measured bars made of platinum and iridium, which would settle international disagreements over the correct length of a meter.) Seventeen nation members joined the original Bureau; fifty-eight now belong, including all the major industrialized nations. The suite of standard units it oversees has grown to seven: the meter (length), the kilogram (mass), the ampere (electrical current), the kelvin (temperature), the mole (volume), the candela (luminosity), and the second.

Among its many duties, the Bureau maintains a single, official worldwide time for all of Earth, called Coordinated Universal Time, or U.T.C. (When U.T.C. was first devised, in 1970, the organizing parties could not agree on whether to use the English acronym, C.U.T., or the French acronym, T.U.C., so they compromised on U.T.C.) Every timepiece in the world, from the hyperaccurate clocks in orbiting global-positioning satellites to the cog-bound wristwatch, is synchronized directly or eventually to U.T.C. Wherever you live or go, whenever you ask what time it is, the answer ultimately is mediated by the timekeepers at the Bureau.

“Time is what everybody agrees the time is,” a time researcher explained to me at one point. To be late, then, is to be late according to the agreed-on time. By definition, the Bureau’s time is not merely the most correct time in the world, it is precisely the correct time. This meant, as I glanced at my watch yet again, that I was not merely late: I was as late as I have ever been and as late as it is possible to be. Soon enough I would learn just how far behind the time I truly was.

·  ·  ·

A clock does two things: it ticks and it counts the ticks. The clepsydra, or water clock, ticks to the steady drip of water, which, in more advanced devices, drives a set of gears that nudges a pointer along a series of numbers or hash marks, thereby indicating time’s passage. The clepsydra was in use at least three thousand years ago, and Roman senators used them to keep their colleagues from talking for too long. (According to Cicero, to “seek the clock” was to request the floor and to “give the clock” was to yield it.) Water ticked and added up to time.

For most of history, though, in most clocks, what ticked was Earth. As the planet rotates on its axis, the sun crosses the sky and casts a moving shadow; cast on a sundial, the shadow indicates where you are in the day. The pendulum clock, invented in 1656 by Christiaan Huygens, relies on gravity (affected by Earth’s rotation) to swing a weight back and forth, which drives a pair of hands around the face of the clock. A tick is simply an oscillation, a steady beat; Earth’s turning provided the rhythm.

In practice, what ticked was the day, the rotational interval from one sunrise to the next. Everything in between—the hours and minutes—was contrived, a man-made way to break up the day into manageable units for us to enjoy, employ, and trade. Increasingly our days are governed by seconds. They are the currency of modern life, the pennies of our time: ubiquitous and critical in a pinch (for instance, when you just manage to make a train connection) yet sufficiently marginal to be frittered away or dropped by the handful without thought. For centuries, the second existed only in the abstract. It was a mathematical subdivision, defined by relation: one-sixtieth of a minute, one thirty-six-hundredth of an hour, one eighty-six-thousand-four-hundredth of a day. Seconds pendulums appeared on some German clocks in the fifteenth century. But it wasn’t until 1670, when the British clockmaker William Clement added a seconds pendulum, with its familiar tick-tock, to Huygens’s pendulum clock, that the second acquired a reliably physical, or at least audible, form.

The second fully arrived in the twentieth century, with the rise of the quartz clock. Scientists had found that a crystal of quartz resonates like a tuning fork, vibrating at tens of thousands of times per second when placed in an oscillating electrical field; the exact frequency depends on the size and shape of the crystal. A 1930 paper titled “The Crystal Clock” noted that this property could drive a clock; its time, derived from an electrical field instead of gravity, would prove reliable in earthquake zones and on moving trains and submarines. Modern quartz clocks and wristwatches typically use a crystal that has been laser-engineered to vibrate at exactly 32,768 (or 215) times per second, or 32,768 Hz. This provided a handy definition of the second: 32,768 vibrations of a quartz crystal.

By the nineteen-sixties, when scientists managed to measure an atom of cesium naturally undergoing 9,192,631,770 quantum vibrations per second, the second had been officially redefined to several more decimal places of accuracy. The atomic second was born, and time was upended. The old temporal scheme, known as Universal Time, was top-down: the second was counted as a fraction of the day, which took its shape from Earth’s motion in the heavens. Now, instead, the day would be measured from the ground up, as an accumulation of seconds. Philosophers debated whether this new atomic time was as “natural” as the old time. But there was a bigger problem: the two times don’t quite agree. The increasing accuracy of atomic clocks revealed that Earth’s rotation is gradually slowing, adding very slightly to the length of each day. Every couple of years this slight difference adds up to a second; since 1972, nearly half a minute’s worth of “leap seconds” have been added to International Atomic Time to bring it into sync with the planet.

In the old days, anyone could make his or her own seconds through simple division. Now the seconds are delivered to us by professionals; the official term is “dissemination,” suggesting an activity akin to gardening or the distribution of propaganda. Around the world, mainly in national timekeeping laboratories, some three hundred and twenty cesium clocks, each the size of a small suitcase, and more than a hundred large, maser-driven devices generate, or “realize,” highly accurate seconds on a near-continuous basis. (The cesium clocks, in turn, are checked against a frequency standard generated by a device called a cesium fountain—a dozen or so exist—which uses a laser to toss cesium atoms around in a vacuum.) These realizations are then added up to reveal the time of day. As Tom Parker, a former group leader at the National Institute of Standards and Technology, told me, “The second is the thing that ticks; time is the thing that counts the ticks.”

N.I.S.T. is a federal agency that helps produce the official, civil time for the United States. Experts at its two laboratories, in Gaithersburg, Maryland, and Boulder, Colorado, keep a dozen or more cesium clocks running at any given time. As precise as these clocks are, they disagree with one another on a scale of nanoseconds, so every twelve minutes they are compared to one another tick by tick to see which are running fast and which are running slow and by exactly how much. The data from the clock ensemble is then numerically mashed into what Parker calls “a fancy average,” and this becomes the basis for the official time.

How this time reaches you depends on your timekeeping device and where you happen to be at the moment. The clock in your laptop or computer regularly checks in with other clocks across the Internet and calibrates itself to them; some or all of these clocks eventually pass through a server run by N.I.S.T. or another official clock and are thereby set even more accurately. Every day, N.I.S.T.’s many servers register 13 billion pings from computers around the world inquiring about the correct time. If you are in Tokyo, you might be linked to a time server in Tsukuba that is run by the National Metrology Institute of Japan; in Germany, the source is the Physikalisch-Technische Bundensanstalt.

Wherever you are, if you’re checking the clock on your cell phone, it’s probably receiving its time from the Global Positioning System, an array of navigation satellites synchronized to the U.S. Naval Observatory, near Washington, D.C., which realizes its seconds with an ensemble of seventy-odd cesium clocks. Many other clocks—wall clocks, desk clocks, wristwatches, travel alarms, car-dashboard clocks—contain a tiny radio receiver that, in the United States, is permanently tuned to pick up a signal from N.I.S.T. Radio Station WWVB, in Fort Collins, Colorado, which broadcasts the correct time as a code. (The signal is very low frequency—60 Hz—and the bandwidth so narrow that a good minute is needed for the complete time code to come through.) These clocks can generate the time on their own, but for the most part they act as middlemen, serving you the time that is disseminated by more refined clocks somewhere higher up in the temporal chain of command.

My wristwatch, in contrast, has no radio receiver or any way of talking to satellites; it’s all but off the grid. To synchronize with the wider world I need to look at an accurate clock and then turn the stem of my watch and set the time accordingly. To achieve even greater accuracy I could regularly take my watch to a shop and have its mechanism calibrated to a device called a quartz oscillator, which gains its precision from a frequency standard monitored by N.I.S.T. Otherwise, my watch will keep its realizations to itself and will soon fall out of step with everyone else’s. I had assumed that putting on a watch meant strapping established time to my wrist. But, in fact, unless I take the measure of the clocks around me, I am still a rogue. “You’re free-running,” Parker said.

·  ·  ·

From the late seventeenth century to the early twentieth century, the most accurate clock in the world resided at the Royal Observatory in Greenwich, England; it was regularly reset by the Astronomer Royal according to the movement of the heavens. This situation was good for the world but quickly became a problem for the Astronomer Royal. Beginning around 1830, he increasingly found himself interrupted from his work by a knock on the door from a townsperson. Pardon me, he was asked. Would you tell me the time?

So many people came knocking that eventually the town petitioned the astronomer for a proper time service; in 1836 he assigned his assistant, John Henry Belville, to the task. Every Monday morning, Belville calibrated his timepiece, a pocket chronometer originally made for the duke of Sussex by the esteemed clockmaker John Arnold & Son, to the observatory time. Then he set off for London to visit his clients—clockmakers, watch repairers, banks, and private citizens who paid a fee to synchronize their time to his and, by extension, the observatory’s. (Belville eventually replaced the chronometer’s gold case with a silver one in order to draw less attention in “the less desirable quarters of the town.”) When Belville died, in 1856, his widow took over; when she retired, in 1892, the service passed to their daughter Ruth, who became known as “the Greenwich time lady.” Using the same chronometer, which she called “Arnold 345,” Miss Belville made the same tour, disseminating what by then was known as Greenwich Mean Time, the official time of Britain. The invention of the telegraph, which enabled remote clocks to synchronize with Greenwich time almost immediately and at lower cost, eventually rendered Miss Belville almost but not quite obsolete. When she retired around 1940, in her mideighties, she still served some fifty clients.

I had come to Paris to meet with the Greenwich time lady of the modern era, the Miss Belville for all of Earth: Dr. Elisa Felicitas Arias, the director of the B.I.P.M.’s Time Department. Arias is slender, with long brown hair and the air of a kindly aristocrat. An astronomer by training, Arias worked for twenty-five years at observatories in Argentina, her native country, the last ten of them with the Naval Observatory; her specialty is astrometry, the correct measuring of distances in outer space. Most recently she worked with the International Earth Rotation and Reference Systems Service, which monitors the ever-so-slight variations in our planet’...