There was a time, when time was not so important. People could make 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.
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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 calculate longitude (pre GPS), you must either know the precise time, or rely on complicated star charts.
At the equator the Earth is moving at 28,000km/hour, so a tiny error calculating time translates to a big distance.
This problem wasn't really solved until John Harrison (1693 -1776) built the first reliable marine chronometer.
Although it was a remarkable piece of engineering, those clocks are not nearly good enough today. Our interconnected world requires incredibly accurate synchronisation, and astronomy and GPS are completely dependent on it. A billionth of a second error in a GPS satellite will put receivers 30 centimetres 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 small number of atomic clocks that are amazingly accurate. 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, so these errors can easily accumulate.
Ultimately, synchronisation always relies on referring to a master source and the very act of looking is a challenge.
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