If ever you are invited to high table at Christ Church College, Oxford, you can afford to be a little late. The dinner gong chimes at 7.15pm – just as university statutes dictate. University statutes are completely silent on what “7.15pm” actually means, though. So Christ Church, a college for which the Gregorian calendar is a historically recent innovation, is still reserving judgment on whether this newfangled Greenwich Mean Time will catch on – and runs five minutes late, on Oxford Time.
If ever you are invited to celebrate complines with the monks of Mount Athos, you might have to be more careful about timekeeping. On this forested peninsula in Greece, Orthodox Christianity’s version of the Vatican, the hour depends on the season. Athos runs on Byzantine time, with the clock reset at dawn each day – here they dismiss other systems as “cosmic time”.
Time, once, was not the tick that tocked in unison in the world’s financial centres, or was sent to our phones in uniform beats from orbiting GPS satellites. Time, once, was a marketplace. More than that, it was a market where you could be a customer for many different kinds of time, at the same time. Now watches are starting to reflect this once more.
Even until recently, when sailors navigated across the Atlantic Ocean, they needed three means of timekeeping. The position of the sun would tell the local time by day, the solar time. The stars would tell a different local time by night, sidereal time. And, so they could use these two times to tell where they were, a clock on board would carry the local time of the home port, set in relation to Greenwich Mean Time. Tables in the nautical almanac, different for each day of the year, told sailors how to convert between them.
A few high-end watches are embracing this plurality again. Blancpain’s Le Brassus Equation du Temps Marchante shows solar time, the Jaeger-LeCoultre Master Grande Tradition Grande Complication shows the 23hr 56min passage of the sidereal day, the Bovet Récital 20 Astérium includes the position of the constellations too, their passage across the heavens once tracked by desert travellers.
To what end? In these days of GPS they are, if nothing else, a reminder that time is as much a philosophical construction as a physical reality. “What then is time?” Saint Augustine asked nearly two millennia ago. “If no one asks me, I know what it is. If I wish to explain it to him who asks, I do not know.”
The fact we, like Augustine, rarely think about the time we use is all the odder because, of all chronological systems, the one we have today is by far the strangest. Greenwich Mean Time, known as Co-ordinated Universal Time, is determined by a caesium atom, but the principles are the same as when it was created. A year is divided into either 365 or 366 equal days, which are divided into 24 equal hours of 60 equal minutes. If that sounds sensible, it is anything but.
Not by any reasonable definition is GMT “true time” for Britain. Except on four days a year it is not even, by the definition humans have used for most of history, the true time at Greenwich, let alone anywhere else. The rest of the time, a sundial at Greenwich would tell a different hour. To understand why, you need to know how we got here.
The first clock was the sun. It was not that time was set by the sun – time was the sun. But in northern Europe, this meant that for much of the year time was hidden amid drizzly greyness. So monks, who needed to divide their day into “hours” so they could pray, turned to water. The evidence for these clocks is scarce. In 1198, there was a fire in Bury St Edmunds in east England and chroniclers say the monks “ran to the clock”. Either they had a sudden urge to record the precise moment the conflagration hit, or the clock contained a large store of water. A 13th-century slate found at a Cistercian abbey in France adds more detail. It describes how to set a water clock, with the duration of an hour different for each day of the year – as at Athos.
This was as it should be. Time was a creation of God, God’s unit of time was the day, and so if the day began later in winter, time needed to reflect that. A system of time that was not in harmony with God’s time was not just heretical but unimaginable.
Then the unimaginable heresy of mechanical clocks arrived. These are often talked about as a revolution in timekeeping. They created the fixed hours that in turn created the Industrial Revolution – enabling workers to be called upon at 8am every day whether in winter or high summer. One point is often missed in this. This was a revolution by necessity, enforced by the literal revolutions of cogs. Variable hours still made more sense, at least until the factory owners came along, but clockwork simply does not lend itself to variance.
In each city from then on clocks were set to the sun, and the day was divided into 24 hours. London time was, given its position 50 miles to the east, five minutes faster than Oxford time, itself five minutes ahead of Bristol time.
Many people have heard what happened next. The railways came, and the fact that – say – a train from New York to Washington, where you travel with the sun, apparently took less time than one from Washington to New York, where you travel against it, began to be a problem. Worse, if you changed trains to go on elsewhere, on whose time did the interchange work? The destination, the start or the location of the interchange? So time was centralised. Just a few pockets like Christ Church were left behind.
But there was a subtler and more significant change that came before that, a change reflected in the true solar time of the Blancpain watch. Within the course of a particular year, the Earth’s rotation oscillates. This oscillation is regular; the year itself remains the same (give or take a second) – but one day compared with another can vary in length by as much as 16 modern minutes. If we define an hour as a 24th of a day, however long a day is, this doesn’t matter. If we define it as a certain number of swings of a pendulum or even – as we do today – the oscillations of a microwave beam when tuned to a caesium atom, it does.
The result is that even at Greenwich a sundial, the most intuitive gauge we have of time, tells a different time from the clock of the observatory – the centre of the world’s time. On only four days a year would a sundial placed on the Greenwich meridian tell Greenwich Mean Time. The rest of the year, its midday would differ from midday GMT as understood by the world. Meantime is not the position of the sun day-to-day, it is an average – a mean – across the year of the period between midnight and midnight as experienced at Greenwich.
Is the sundial wrong? Not if you consider time to be related more to night and day than to a caesium atom. Yet atomic time is the time we work on, and we can’t turn the clock back. Russell Foster, a professor of chronobiology at Oxford, laments this. His work, looking at sleep and circadian rhythms, to a large extent deals with the consequences of humans existing on a time standard that follows clocks rather than light.
For him, the chronological rot set in during the Middle Ages. “The worst thing, the absolute worst thing, is that first we create these hours so we can have an Industrial Revolution and spend our lives working nine until five. And then what do we do? What do we do when people escape and retire? We present them with a clock.”