Time Synchronisation

Technology and the Importance of Time

This article explores the concept of time, how it is measured and how our technologies have required more and more accurate ways of measuring time.

It is a question that has perplexed philosophers and scientists since the dawn of man, ‘what exactly is time?’ and it has only been in our recent history that we have started to discover answers, thanks to Einstein and his work on special and general relativity.

We now know time is not the abstract concept we first thought it was, we also know it is not constant and is relative to different observers throughout the universe with the speed of light being the only constant in the universe.

In other words if the speed of light has to be the same for everybody then someone travelling at close to such a speed would find time slow down.

Fortunately as all humans live within the boundaries of the planet Earth it means the passing of time is very similar for us all (or so minutely different as to be impossible to measure). However, technologies such as satellites and GPS systems have to take into account this altering state of time otherwise they would become wholly inacurate.

As humans have progressed, telling the time with ever increasing accuracy has become more and more important. Historically, knowing the time was not so imperative. People needed to know the correct day to plant crops or when sunrise and sunset happened but accuracy was not a preoccupation.

However, since the invention of the mechanical clock followed at the turn of the twentieth century by electronic clocks, humans have started to rely on more and more accuracy for their technologies.

Seafaring, aviation and now space travel mean that humans have sought more and more accuarte ways of keeping time.

In the 1950’s atomic clocks were developed which were so accurate it was discovered that the revolution of the Earth, something we had based our timescale on for centuries, was no where near as accurate as these new clocks.

Now technologies such as the Internet, the Global Positioning System and satellite communication requires absolute precision as light can travel 300,000 km every second meaning accuracies of a split second could mean our satellite navigation systems could be out by thousands of miles and computer trading would be nigh on impossible.

Fortunately a global time scale, UTC (Coordinated Universal Time), has been developed and is based on the time told by atomic clocks. This allows systems all over the world to be synchronised to the exact same time.

Computer networks use the NTP protocol (Network Time Protocol) to receive a UTC timing reference and synchronise all machines on a network to that time.

NTP servers can receive a time reference over the Internet (although not very secure) from a national radio transmission (as long as the receiver is within range of a suitable transmission) or from the GPS network (via a rooftop GPS antenna).

This article describes what happened when Europe adopted the Gregorian calendar and the problems we still face today trying to synchronise with movement of the Earth.

Have you ever gone to bed one night and wondered just where the day went? Well could you imagine waking up to discover that eleven days had vanished completely? That is just what happened in 1752 when the entire inhabitants of Britain and America went to bed on Wednesday 2 September, only to awake on Thursday 14 September.

However, it wasn’t an epidemic of sleepy sickness or even a mass dose of laziness that kept the entire populace in bed but merely the authorities attempting to synchronise with the rest of the world by adopting the Gregorian calendar.

The Julian calendar (named after Julius Caesar) had been in use since biblical times but was finally phased out throughout Europe in the 1582 but it took the resolute Brits and Americans another two hundred years to follow suit.

And if the painter Hogarth is to be believed the populace didn’t take too kindly to it either, with people taking to the street demanding the return of their missing 11 days and even reports of rioting.

Then why change? That was what the British authorities had been saying for two hundred years ever since Pope Gregory XIII had replaced the Julian calendar in Europe two hundred years before.

However, the reason for the original change was that the Julian calendar didn’t allow for enough leap years (they were omitted in years divisible by 100 but not divisible by 400 – what were the Romans thinking?) and the seasons were slowly becoming out of sync with the calendar. The situation was now becoming even more intolerable in Britain, playing havoc for farmers – who had no idea when to plant their crops, finally the authorities were to switch over and fast forward the whole country 11 days.

However this synchronisation problem has always been with us. We have traditionally tried to base our calendars around the movement of the Earth to allow us to predict seasons and know when the summer and winter will fall. However, we may have sorted out the leap years (caused by the fact the Earth takes 365 and a quarter days to travel around the Sun) but trying to base a calendar around the movement of the Earth will always lead to problems.

The Gregorian calendar worked fine until the 1950’s when the atomic clock was developed. The atomic clock worked so well – providing timing information accurate to a second in several millions of years – that we soon realised that our clocks were now far more accurate than the Earth itself.

The Earth is actually slowing down in rotation and if nothing was done then eventually noon would fall at night and vice-versa (albeit not for several millennia) but don’t worry you are not about to wake up in the middle of next week. The solution is the adding of leap seconds and 33 have been slotted into the end of our years since the 1970’s.

The decision to insert a second is usually taken six months before after careful monitoring of the Earth’s rotation. A calendar based on the movement of the Earth may seem less relevant today but with a Global Positioning System (GPS), a global time-scale (Coordinated Universal Time), and computers all synced together around the world using NTP servers (Network Time Protocol) it is imperative we can all tell the right time.