Atomic Clock - Keeping the World Ticking

When most people think of the digital age and its computers, satellites and mobile phones, the silicone chip is at the foremost of people's minds. Yet, despite its importance in shaping the world around us, many of the technologies that we take for granted would not be possible without the atomic clock.

The first atomic clock was developed in 1955 by British born Dr Louis Essen who worked during WWII,  on high-frequency radar which led him to develop a resonance wavemeter, that was used to successfully measure the speed of light.

Using the same technology he developed the first accurate atomic clock in 1955 at the National Physical Laboratory in the UK. It was based on the resonance of the caesium atom.

According to quantum theory, atoms can only exist in certain quantized energy states depending on the orbits of electron about their nuclei. A cesium clock operates by exposing the atoms to microwaves until they oscillate at one of their resonant frequencies. It was discovered that a caesium atom would resonate at 9,192,631,770 hertz (times a second).

Because of this exactness in resonance and the high number of oscillations atomic clocks (sometimes referred to as caesium oscillators) are exceptionally accurate. Essen's first device was accurate to a second in a thousand years but the next generation of atomic clocks are now so accurate they will not lose a second in several hundred million years.

Because of this high level of accuracy problems have occurred in the way we structure out timescales. traditionally GMT (Greenwich Meantime) has been the basis of time. GMT is based on the principle that the Sun is highest in the sky at noon (or over the Greenwich meridian line). Unfortunately as atomic clocks are so accurate it has been discovered that the Earth itself is not as precise in its revolution and is often slowed by the gravitational effects of the moon.

If nothing was done about this then eventually International Atomic Time (TAI - the time told by atomic clocks) would drift out of synchronisation with GMT and eventually night would drift into day (albeit in several millennia).

Coordinated Universal Time (UTC), was developed to counter this. It is based on TAI but accounts for the slowing of the Earth's rotation by adding occasional 'leap seconds', 33 of which have been added since the 1970's.

Atomic clocks are crucial for telecommunication networks.Voice and data transfers that have to travel around the world in packets needs to be time-stamped as time is the only reference point a computer can use to reassemble the packets.

Atomic clocks have also made satellite communication possible, as the speed of light is so fast (900,000 km a sec) a tiny variation in time could create massive differences. Global Navigation Satellite Systems (GNSS) such as GPS (Global Positioning System) are heavily dependent on atomic clocks as the timing signal is what a GPS receiver uses to triangulate a location.

Thanks to atomic clocks and devices such as the NTP server (Network time Protocol) that distributes an atomic clock timing reference received though either a radio or GPS receiver, to a computer network, synchronising the computers to UTC. Thanks to technologies such as this, electronic transactions can now be done within five nano-seconds. Without such technologies online trading such as the stock exchange, buying an airline ticket and even Internet auction sites would not be possible.