Ask Fuzzy: The challenge of staying on time

There was a time, when time was not so important. People could arrange a date and say "meet me here at noon", and that was near enough. Since then, our need to be precise has become ever more pressing.

Knowing the time was a crucial problem for early navigators. Finding latitude is fairly simple because the north-south position of stars doesn't change much during the course of a day.

Longitude is much more difficult because the Earth is spinning, and the east-west alignment of the heavens changes constantly. It rotates 360 degrees in a day, which is 15 degrees every hour.

If you want to know longitude – pre GPS – you must either know the precise time, or rely on complicated star charts.

At the equator the Earth is moving at 28,000 km/hour, so a tiny error calculating time translates to a big distance. We can see evidence today, of how early seafarers paid the price as they sailed towards the north-west coast of Australia. They'd pick up the fast trade winds, then at the right moment, "turn left" – north towards Indonesia. The number of shipwrecks shows the difficulties.

This problem wasn't really solved until John Harrison (1693-1776) built the first reliable marine chronometer.

Today, those clocks are not nearly good enough. Our interconnected world requires incredibly accurate synchronisation.

Astronomy and GPS are completely dependent on it.

A billionth of a second error in a GPS satellite will put receivers 30centimetres off.

Even with sophisticated electronics, it's difficult to synchronise clocks. TV broadcasters know this. Two signals going via different paths can be out of alignment by the time they arrive. When that happens, we see lip-synch errors.

The internet uses a mechanism called Network Time Protocol, and time signals are also sent via means such as GPS. These rely on a accurate atomic clocks.

They watch the electrons orbiting caesium atoms, oscillating at 9,192,631,770 times per second.

It takes only minor lag delays in the electronics or data transmission to introduce errors. Modern communications systems contain a vast number of hops, and these errors can easily accumulate.

Ultimately, synchronisation always relies on referring to a master source, and the very act of looking is a challenge.

Response by: Rod TAylor, Fuzzy Logic

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