Artists impression of an atomic clock for space missions.

An artist’s impression of NASA’s Deep Space Atomic Clock. Atomic clocks are used in space missions to synchronise with clocks back on Earth.

Image: NASA

It’s a question that millions of people ask every day: ‘What’s the time?’ Knowing the time is an essential part of everyday life and important to scientific research as well.

Depending on their field of research, scientists are interested in time in different ways. A chemist might study what happens in the first second of a chemical reaction, while an astrophysicist might be interested in the origins of the Universe, billions of years ago. Regardless of what they’re studying, scientists often need good ways of measuring time.

This is where clocks come in. A clock is used to measure time, but there are many ways of doing this. Different kinds of clocks have been around for thousands of years. Early clocks used phenomena such as the apparent position of the Sun in the sky, or the flow of water to measure time.

Once the pendulum was understood, much more precise clocks were invented. A pendulum is a hanging weight that is able to swing freely. The time taken for a pendulum to swing side to side depends on its length and each swing takes the same amount of time. A problem with pendulum clocks is that as they eventually lose energy, the pendulum swings less and they lose time.

A pendulum is an example of a harmonic oscillator – a system that vibrates at regular intervals. Although most pendulum clocks have been replaced with electric ones, all clocks still rely on oscillators.

The most accurate clocks today are atomic clocks. In these clocks, the oscillators are atoms moving from one energy state to another. They are extremely precise – the best atomic clocks only lose or gain a second after about three billion years.

At the moment, atomic clocks are restricted to a few laboratories. However, a group of researchers claim advances in fibre optic technology could change this. They say atomic clocks could connect to the internet, allowing more people to access this timekeeping. This could help scientists who require this level of precision, but don’t have an atomic clock of their own.

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