Atomic Clocks

Not long ago the idea of owning a personal atomic clock would have sounded like something out of science fiction. Today you can buy an "atomic" clock or watch in many high street stores.

What Is An Atomic Clock?

Scientific

Strictly speaking, an atomic clock is a high-tech piece of equipment that uses the resonance of atoms as a counter. The principle is analogous to the quartz clock: in the same way that quartz crystals vibrate at a certain frequency, so do atoms (eg caesium). The difference is that atomic vibrations are much more reliable and provide much greater degrees of accuracy.

Highly accurate atomic clocks are used to record International Atomic Time (TAI). This is then converted to Coordinated Universal Time (UTC), the worldwide time standard.

Domestic

In practice the term "atomic clock" is often commonly used for something far cheaper and easier to manage. Even the best clock available to buy in the store is unlikely to be counting the microwave electromagnetic radiations from quantum transitions of caesium!

So, how do atomic clocks work?

Many countries have a system of radio transmitters that broadcast a time signal from the reference atomic clocks that record UTC. Your domestic "atomic" clock will pick up this radio signal and set itelf accordingly. The advantages of this are that the time is kept accurately in sync with the master signal and there is usually no need to manually adjust for daylight saving time.

So calling it an atomic clock is a misnomer. It's actually a radio controlled clock that shows atomic time as kept elsewhere. By this definition any form of radio-controlled clock can thus be described as "atomic", from wall to desk, traditional to projection, alarm or silent.

As with all other areas of life, the technology keeps getting smaller - in 2004 the US National Institute of Standards and Technology (NIST) demonstrated a chip-scale atomic clock.

External Links:
NIST: Basic Questions and Answers about Chip-Scale Atomic Clocks