<b> A brief history of time: Time lords</b>
<i>American scientists want to change the way the world's clocks are set, abandoning methods used since the dawn of history</i>
By Cole Moreton. <i>The Independent</i> 01 January 2006

What did you do with the extra second last night? Take another cup of kindness? Let a New Year kiss linger on the lips? Wonder why the radio was playing an extra pip?

If you didn't even notice the leap second being added to all our lives at midnight then that's a shame, because it may be the last. Time, the universal notion that underpins everything we do, is changing: becoming ever more accurate and powerful, it may also be about to split apart.

The trouble is that the experts who are supposed to tell us what time it is cannot agree how to do so. The time lords are falling out, as one group argues for the world to abandon ancient methods of timekeeping and rely solely on super-accurate atomic clocks instead.
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Systems such as the new Galileo satellite, launched last week, use atomic time to keep planes in the air and cities moving. American scientists believe it is time to measure out our lives only according to the rate at which the atoms of caesium-133 vibrate. They are opposed by equally passionate astronomers who are keen that we should all continue to measure time by using the movement of the sun in the sky to define a day.

These two versions of time have drifted 32 seconds apart, because the rotation of the Earth is irregular and slowing down. But since 1972 they have been reconciled to within 0.9 seconds of each other using leap seconds announced from the Paris Observatory. This produces a compromise called Co-ordinated Universal Time, which is why the most accurate clocks in the world were set to show an extra second as 23:59:60 last night, before 00:00:00.

Many other clocks and computers also had to be reset, by operators who really did not see the point. They call leap seconds a dangerous and unnecessary disruption to the complex software used to run everything from mobile phone networks and power grids to traffic lights and life-support systems. That is why American scientists have proposed abolishing the leap second - or at least letting their own version of time drift as much as an hour away from old-fashioned "sun time" before it has to be reset, which could take hundreds of years. The prevalence of technology would then make atomic time the standard, and the old kind just a minority pursuit.

The world's top techies first challenged the stargazers at a meeting in Geneva in November, but they agreed to disagree until after last night's leap second. The debate continues to tick away like a time bomb inside the International Telecommunications Union, where governments and private companies work together to keep the blizzard of emails, radio and television broadcasts, faxes, phone calls, satellite signals and internet activity in the world from meltdown. All these things rely on accurate digital sources of time - which is why technology and the corporations funding it are pushing a debate that could lead to the most profound change in the way we measure time since the beginning of human history.

We have always instinctively measured time according to the movement of the sun. The Egyptians had sundials dividing daylight into 10 parts, plus one for dawn and one for dusk. Water clocks measured out the time from when the sun appeared overhead at noon to when it returned the next day, but the use of 24 identical hours became widespread only with the weight-driven mechanical timepieces of the 15th century.

This story is told at the Royal Observatory in Greenwich, London, where tourists from Australia and Japan stand astride the meridian and have themselves photographed with one foot in the eastern hemisphere and one foot in the west. "The centre of time and space," is what Greenwich calls itself, with language echoing the days of certainty, precision and empire. (The train drivers of the Raj were regulated by time defined here.)

For £1, Cindy Marshall from Nebraska buys a certificate declaring to one-100th of a second that she was at this Unesco World Heritage Site at 15.09.05.01. "That's so cool," she says. "How do they determine that?" Then she asks what everybody asks at Greenwich, even now: "Is my watch right?"

People have been checking their timepieces here since Charles II set up the Royal Observatory to seek a solution to the problem of longitude. Sailors needed to know where they were in the world, so the first Astronomer Royal, John Flamsteed, was appointed to map out the stars and prepare accurate charts of their movements to aid navigation. It was decided that zero degrees longitude should be at Greenwich: then if sailors knew when it was noon in London they could use the amount of time it took for the sun to appear over their own head to calculate their position. But no clocks worked at sea, until John Harrison invented his watch H4, and was awarded, after considerable wrangling, a prize by the Crown.

There was still no standard time in Britain until the railways came. That noon in London was 11.44am in Plymouth did not matter until there was a timetable to observe. A master clock was set up at Greenwich in 1852 to send electrical pulses out to clocks across the country. Some called this "railway aggression", resenting government interference in their lives, but by 1855 nearly all public clocks in the country kept the same time.

Similar things were happening across the world. In 1884, delegates from 25 countries met in Washington to set up a series of time zones. For every 15 degrees of longitude there would be an hour difference. There had to be a base level and there was some dispute about whether it should really be at Greenwich - but since American railways and most of the ships in the world kept time on that basis, it was agreed. So Greenwich acquired the status it is so proud of today, with £15m being spent on four new galleries and a planetarium to celebrate its position at the heart of time. It is still at the prime meridian, but soon even that may be only history. If the world goes over to atomic time, the rotation of the earth will mean the meridian gradually slips eastwards.

"Greenwich is just a museum now," said Peter Whibberley, senior time scientist at the National Physics Laboratory in Teddington, Middlesex, where two scientists built the first working atomic clock in 1955. It used caesium-133, as modern versions do, although they are more accurate. There are 230 of them in 65 laboratories across the world, and 100 in orbit around the earth, all sending data to the International Bureau of Weights and Measures in Paris. Mr Whibberley is the man who added the leap second to the caesium clock which is kept at Teddington in stable laboratory conditions, with humidity, temperature and vibrations all controlled.

At the NPL, a second is not defined as a tick-tock, a 60th of a minute or the time it takes to fall in love, but as 9,192,631,770 cycles of electromagnetic radiation in an atom of caesium-133. The method is apparently accurate to within one second every 60 million years. Mr Whibberley reset his clock in advance of New Year's Eve. "Apart from having a quick drink, there's not much you can do with an extra second," he said."That's probably what I'll be doing."

Extra drink or not, the NPL is not in favour of only using atomic time. It sympathises with astronomers, whose work tracking distant stars would be thrown into chaos. The Royal Astronomical Society said last week: "Over a few decades, when the error might grow up to half a minute or so, one can imagine the arguments that lawyers and insurance companies might have about whether an event had occurred before or after midnight."

Nevertheless, the heads of American technology corporations tend to get their way, and they seem to think of Greenwich Mean Time and the rotation of the Earth as quaint, old-fashioned, a bit wobbly - and 32 seconds slow. So if you saw someone pop their cork half a minute early last night, it was probably one of them. Ahead of their time or out of step? Only time will tell.

From sundials to atomic clocks

1: Our understanding of the passage of time has always been based on the movement of the sun and Earth. The ancient Egyptians had sundials dividing daylight into 10 parts plus dusk and dawn. The rotation of the Earth, "moving" the sun from directly overhead on one day to the same position on the next, has formed the basis of time-keeping ever since. This includes Greenwich Mean Time, whose status as a universal standard for the world is under threat. But everyone agrees that 24 hours equals one day

2: The Greeks were the first to use water clocks regulated by a constant drip from a stone vessel. The same principle powered the first known mechanical clock, which was built in a tower 30ft high by the astronomer and inventor Su Song in China in 1088. A globe inside the tower rotated once a day

3: The next step forward was to use a system of falling weights to drive the mechanism, instead of water. This made possible the large public clocks that would be built into towers in town centres across the world, starting with Italy in the 14th century

4: The need for sailors to know where they were led to agreement that the position of the sun at noon in Greenwich, London, should be considered 0 degrees longitude. This called for a clock that stayed accurate at sea in any temperature and regardless of motion. H4 was invented by John Harrison

5: Until the coming of the railways it did not matter that noon in London was 11.44am in Plymouth. But in 1852 a master clock was set up to send electrical pulses from Greenwich across the country. Despite some local opposition, soon all British public clocks were set by it

6: In October 1884, delegates from 25 countries met in Washington to decide on a system of time zones for the whole world. Since most of the vessels at sea already used charts with Greenwich as 0 degrees longitude, this was declared the prime meridian

7: The position of Greenwich as the centre of time was first threatened when quartz clocks were made in the 1920s. They count the seconds using the vibration of electricity through crystals, and have nothing to do with the sun. They made good cheap watches, but were soon surpassed in accuracy

8: Time changed for ever when the first atomic clock was built at the National Physics Laboratory in Middlesex in 1955. Accurate to within a second every 300 years, it established a new standard, far more reliable than the rotation of the Earth

9: The modern atomic clock uses the gas caesium-133 in a vacuum. Lasers are used to push the atoms together into a ball, which cools them. The ball is then projected a metre upwards through magnets and a microwave chamber, which heats the atoms. Any that have absorbed energy glow as they fall back down to where they came from, past a detector

10: Each atom is like a mini solar system, with electrons orbiting a central nucleus. As the electrons absorb or release energy, they move up or down to different orbits. This produces electromagnetic radiation, which vibrates at a precise frequency. Recording this vibration with the detector in the clock gives scientists a measure of time accurate to within a second every 60 million years: one second equals 9,192,631,770 cycles of radiation from a caesium-133 atom. The need to reconcile this new standard of time with the old version leads to leap seconds