Posted by Richard N Williams on January 22nd, 2008
What time is it? One of the commonest questions uttered around the World but what exactly are we asking? You ask someone in China what the time is then you will certainly get a different answer if you ask an American, obviously their time-zones are on the opposite side of the world.
But what if you ask two people in the same room as you? You may get the same answer from them both but then again one person’s watch may be a minute or two faster.
When we ask the time then what we are really asking for is a rough estimate for the time zone that we are in. Some watches are more accurate than others but it is often enough for our day to day needs.
But what if you need to know the exact time and what if you need to know what that time is another country too. Perhaps you have bought an airline ticket; it would be disappointing to turn up at the airport only to be told that your ticket was sold to somebody else in as the clock at their travel agent was slower than the one where you bought your ticket.
So how does global industry keep accurate time with one another? The answer is quite simple and it is called Coordinated Universal Time or UTC.
The International Bureau of Weights and Measures (BIPM) acts as the official time-keeper for the globe and started UTC in 1972 after the development of atomic clocks.
The atomic clock was first developed in the late 50’s when it was discovered the atom caesium-133 resonates at an exact frequency of 9,192,631,770 every second. This frequency was so exact that atomic clocks developed an accuracy of one second in 1.4million years and The International System of Units defined the second as the frequency of the caesium-133 atom and an international unit for measuring time was born.
However, atomic clocks are even more accurate than the Earth itself which is actually slowing in its rotation. This slowing is only small but if the standard system of time, UTC, didn’t compensate for it, eventually midnight would fall in the middle of the day (although that would take a millennia or two) so leap seconds are added every few years to compensate.
The only problem with UTC timepieces is that atomic clocks are enormous in both size and cost. In fact they are generally only to be found in large scale physics laboratories such as NPL (National Physics Laboratory, UK) or MIT (Massachusetts Institute of Technology, US).
Then how does the rest of the world keep track of UTC time? The time told on these vast atomic clocks is broadcast via radio broadcasts or the GPS satellite system (Satellite Navigation is reliant on UTC as without it a satellite can’t tell exactly where a receiver is).
Most computer networks are sycnhronised to UTC time either over the Internet (which isn’t secure and only recommended for home users) or through specialist GPS or radio time servers. These time servers make use of NTP (Network Time Protocol) which has been developed over the last 25 years to keep computer networks synchronized so they do not have to rely on their inaccurate internal clocks.
NTP servers and UTC have allowed industry to become truly global and made possible technologies such as communication satellites, mobile phones, sat-nav and ATM’s that we all take for granted.