# How does an atomic clock work?

Asked by: Rami### Answer

The term atomic clock is the general name used to describe any variety of time keeping devices based on the regular vibrations associated with atoms.One of the first atomic clocks or as it is also known the ammonia clock. Was developed by the National Bureau of Standards, and was based on the measurements of the vibrations of atoms of nitrogen, oscillating back and fourth in ammonia molecules at a rate of 23,870 vibrations per second.

The modern day atomic clocks are based on caesium atoms. The spectrum of caesium includes a feature corresponding to radiation with a very precise frequency of 9,192,631,770 cycles per second. One second is now defined as the time it takes for that many oscillations of the radiation associated with this feature in the spectrum of caesium. This type of clock is known as a Caesium clock and it is accurate to one part in 10,000 billion, or one second in 316,000 years.

Even more accurate clocks have been developed using radiation from hydrogen atoms. They are known as Hydrogen Maser Clocks, and one of these clocks, at the US Naval Research Laboratory in Washington, DC, is estimated to be accurate to within one second in 1.7 million years. In principle, clocks of this kind could be accurate to one second in 300 million years!

Answered by: Dan Summons, Physics Undergrad Student, UOS, Souhampton

'A theory with mathematical beauty is more likely to be correct than an ugly one that fits some experimental data. God is a mathematician of a very high order, and He used very advanced mathematics in constructing the universe.'

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**Paul Dirac**(

*1902-1984*)