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When Time Was New

Time is a moving image of eternity.

— Plato

Not long ago I mislaid my watch. I remembered that I had taken it off in the house, so I figured it would turn up sooner or later. It did, but in the meantime I learned something tangible about the ubiquity of time. Even without a watch strapped to my wrist, I never had to look far to find out what time it was. There is the digital readout on the computer I am using to write this piece, the one on my other computer, the one of my cellphone, the one on our VCR, the one on our stove, the one in each of our cars, the clock radio in our bedroom and so on. Even without setting an alarm, I wake up at approximately the same time every morning, which suggests that I have even internalized the time of day.

Time is so ingrained in our sense of the world that we have trouble understanding that time didn’t always exist. (I am speaking here of clock-time itself, not what is measured by the movement of hands on a dial.) There are still hunter-gatherer tribes in remote parts of the world that have no concept of time as we understand it. They have no words for it in their language. Nor do they have grammatical constructions to delineate actions that occur in what we think of as the past, present or future.

Early agricultural societies had to find ways to track the passing days so they would know when to plant and when to harvest. Bone carvings found at a Neolithic cave site in France's Dordogne Valley show the waxing and waning of the moon over a period of several months, presumably to help farmers keep track. The earliest calendars, dating from the Bronze Age, were based on the phases of the moon.

The invention of sundials and water clocks enabled the ancients to divide the days into hours. They were often viewed as a mixed blessing by those who found their lives were no longer regulated by the sun but instead by these implacable man-made devices. Sundials were first introduced to Rome as a spoil of war by the Roman consul Manius Valerius Maximus during the First Punic War in 263 BCE. Erected atop a triumphal column in the Roman Forum, the sundial was the first of many throughout the city that came to regulate every aspect of civic life. In a speech attributed to the comic playwright Plautus, a character exclaims, “The gods damn that man who first discovered the hours, and— yes— who first set up a sundial here, who’s smashed the day into bits for poor me!”

The progress of time from then until now has mostly been one of smashing the day into smaller and smaller bits. Hours became minutes became seconds — each step made possible by advances in technology. Medieval monks invented mechanical clocks because they needed a way to pray before the sun came up. Mechanical clocks kept time when it was dark or overcast, but they gradually lost momentum as they wound down. This problem was solved by a saw-toothed mechanism called an escapement whose back-and-forth movement enabled clocks to maintain a steadier pace. Escapements made it possible to count off the seconds and also literally made a clock tick.

The process of smashing time into smaller and smaller bits continues apace. Technology enables us to measure time in millionths of a second (microseconds), billionths of a second (nanoseconds), all the way down to quadrillionths of a second (femtoseconds) — the timescale of motions within molecules. Timepieces are now more accurate than the earth’s rotation on its axis, which is accurate to within 0.0017 seconds per century.

This raises an interesting practical and philosophical question. If units of time are calibrated in multiples or fractions of a day, which is determined by the earth’s rotation on its axis, what exactly is being measured when the earth’s rotation is no longer accurate enough? As it happens, an atomic clock calculates time based on the oscillations of a cesium atom, not on planetary motion. The cesium atom functions as kind of an escapement, oscillating at a steady 9,192,631,770 cycles per second.

When we say an oscillating cesium atom is a more accurate time-keeper than the earth’s rotation, what do we mean? Accurate in relation to what? The assumption is that there is some absolute measure of time that exists apart from anything we can point to in nature, whether a spinning planet or a vibrating atom. Issac Newton said as much in his Principia: “Absolute, true, mathematical time, of itself, and from its own nature, flows equably without relation to anything external.” Except this turns out not to be the case, as Einstein demonstrated in laying out his special theory of relativity.

Time is so deeply embedded in our language and culture that we find it virtually impossible to see it has no tangible existence apart from the instruments we use to measure it. It helps to put ourselves in the shoes (sandals?) of those Romans for whom time was brand new. The comic playwright Plautus’ character complained about the man “who first set up a sundial here, who’s smashed the day into bits for poor me!” We tend not to think about time as something that can be smashed into bits. Our starting point is not time as a seamless unfolding of events but time that is already fractured into hours, minutes, seconds — and increasingly into tiny fractions of a second.

What then do we mean when we talk about time? “Time is what a clock measures,” Einstein concluded, which sounds at first like a bit of a tautology. However, he may have been getting at something profound. Einstein’s key insight was that time boiled down to the simultaneous occurrence of two events. He used the example of a train arriving at seven o’clock with the small hand of a watch pointed to the numeral seven on the dial. In an earlier era it might have been the position of a shadow on a dial as the sun moved across the sky or scratchings on a bone carving with the phases of the moon. In other words, time doesn’t exist unto itself but only in relation to something external. If time were truly independent of anything external, it would be the same for every observer. But it’s not. According to Einstein’s special theory of relativity, time speeds up or slows down according to the velocity of an observer relative to a given frame of reference. The conclusion seems inescapable: whether calibrated in hours, minutes, seconds or tiny fractions of a second, time can never be anything more than the measure of its own ticking.

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