Time running out for current length of a second as optical clocks arrive in space

Optical clocks could make GPS navigation systems much more accurate, but would also involve changing the length of a second by an incredibly tiny amount

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The Independent Online

Time is running out for the current length of a second after an “optical clock” was sent into space for the first time.

Such clocks are up to 1,000 times more accurate than the current international standard, which dates back to 1967 and is based on the natural oscillation of an atom of caesium, rather than the swing of a traditional pendulum.

While no one would notice the difference in everyday life, optical clocks would be extremely useful for a number of reasons.

For example, it would enable GPS navigation to be accurate to within a few centimetres, rather than a few metres. It would also help manage electricity grids and computerised financial networks.

But changing the way a second is defined – currently 9,192,631,770 cycles of the microwave signal produced by caesium – to about 429,000 billion cycles from a strontium atom used in some optical clocks, would also inevitably introduce a tiny error, changing its length ever so slightly.

Writing in the journal Optica, researchers described how they had successfully sent an optical clock into space – a journey they would need to survive if they were to be used on the satellites providing GPS signals.

Researcher Dr Matthias Lezius, of Menlo Systems, an international firm based in Germany, said: “Our device represents a cornerstone in the development of future space-based precision clocks and metrology. 

“The optical clock performed the same in space as it had on the ground, showing that our system engineering worked very well.”

GPS works by a ground-based device, such as a smartphone, contacting at least four satellites, which each provide a time stamp. This is then used to calculate the position of the device.

One key part of an optical clock is a “frequency comb” laser, which divide the incredibly fast oscillations of the atoms used into lower frequencies that can be counted and turned into a measure of time.

Until recently the laser was a large complex device, but the Menlo researchers developed one that weighed just 22kg and was 22cm across. It was also rugged enough to withstand the extreme acceleration of blast-off on a rock and needed just 70 watts of power.

The optical clock sent into space only had about a tenth of the accuracy of the current atomic clocks used for GPS, but was designed simply to test its capabilities in the microgravity of space.

The researchers now plan to develop an improved version that will be sent into orbit towards the end of next year.

It will be made even more robust so it can withstand the extreme cosmic radiation experienced in space for several years.

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