“What then is time? If no one asks me, I know: if I wish to explain it to one that asketh, I know not.” – St Augustine, Confessions AD397-398

ONCE upon a time, people were happy to regulate their lives around the movement of the Sun, Moon and constellations. These heavenly bodies signalled the start and end of the seasons, when to go to war and which religious ceremonies would be held at particular times of the year.

Ancient philosophers thought time was unreal, an illusion, while the Romans put it to practical uses - such as controlling their vast empire.

Although time is crucial to keeping our modern world working, people throughout history have been aware of its importance / Image: Istockphoto

Egyptian engineers built massive obelisks to track the Sun’s movement over days and water clocks, or clepsydra, to measure the passage of hours.

By 45BC, the Roman world rose and set according to a simple solar calendar divided into about 365 days divided into 12 months, with one ‘leap’ day added every four years in years evenly divisible by four.

Arab and Chinese engineers built the world’s first mechanical clocks by the 11th century, with Arab scholar Al-Jazari documenting up to 50 of the devices and the instructions to assemble them.

Technology was redefining the basic unit of time, not down to the day, but the hour.

The first personal watch was built in Germany in 1502 and a century later, the Swiss built the first clocks displaying minutes and seconds.

In 1582, Italian astronomer Galileo Galilei used the swing of a pendulum to measure intervals of time and in 1656 Dutch astronomer Christian Huygens developed short pendulums which beat several times a second, with an error of less than one minute a day.

Technological advances over the next few decades reduced that margin of error to a few seconds a day.
Then trains arrived - forcing timekeepers to develop better ways of not just measuring, but staying on time. It was time for time to be tamed.

In 19th century Britain, railroads ran on London time determined by the Royal Observatory at Greenwich.

Timekeeping technology took a big leap in 1928 when Bell Laboratories in the United States built the first crude quartz-crystal clock that by 1939 replaced the mechanical clocks at Greenwich Observatory.

In 1949, the US National Bureau of Standards built the first atomic clock, accurate to up to a billionth of a second a day.

Since 1967, the International System of Measurements has based its unit of time, the second, on the spin properties of caesium atoms.

Atomic clocks provide a primary frequency standard to define Coordinated Universal Time, or UTC, which is the official world time computed in Paris at the International Bureau of Weights and Measures. The UTC is based on the average of the world's atomic clocks.

The accurate measurement of time is critical in civil aviation, navigation and communications, both on the earth and in space.

In Australia, the National Measurement Institute in Sydney is responsible for keeping accurate time under the National Measurement Act of 1960.

Atomic physicists ensure caesium clocks work properly, relative to clocks around Australia and overseas.

The world lives on atomic time, for now.

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