Time to test space-time

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How accurate must time be when testing Albert Einstein’s ideas about space-time?

At least to the accuracy of 1 second over 300 million years it seems.

A University of Western Australia research group is building an optical lattice clock based on ytterbium atoms which will be accurate to a new level.

Atomic clocks are used to keep accurate time. They catch signals emitted by electrons when they change energy levels.

 The WA team are building a highly accurate clock using ytterbium. When finished it will form part of a ground station in Western Australia and play a role in a European Space Agency (ESA) mission which will perform experiments using time from the International Space Station (ISS).

The ESA space mission, the Atomic Clock Ensemble in Space, ACES, will launch in 2017. By then, the WA team’s work will reach a milestone.

ESA's mission will compare clocks under different gravity levels allowing researchers to test Einstein’s theories on space-time among other things. Time is linked to gravity and time passes faster at the top of Mt Everest, for example, than at sea level. The ACES will make more precise measurements than can be done on earth.

France’s space agency delivered its atomic clock known as Pharao to the ESA in 2014. It will be used in the ISS experiment. The Pharao clock is accurate to 1 second over 300 million years. It uses the caesium atom – popular in accurate time-keeping since 1967 when atomic frequencies of the ground state of the caesium-133 atom was used to officially define one second in time.

Another kind of clock called the Space Hydrogen Maser, which uses hydrogen atoms to keep track of time, will also be sent up to the ISS.

With these two clocks, ACES will provide scientists with a highly stable time reference in space.

The ESA project will link together atomic clocks on the ground in Europe, USA, Japan and Australia. This will be done through a dedicated microwave link which will send the ACES timing signal to the ground allowing space-to-ground comparisons of the clocks.

It’s scientific knowledge from the 1960s that is being improved upon as other elements are being incorporated into atomic clocks, improving their accuracy for space applications.

So well done to the WA team. This will be an exciting project to follow in the next few years.

Image credit: WebElements,