China’s Spacebound Atomic Clock Will Stay Accurate for One Billion Years

A new Chinese space laboratory houses the world’s first cold atomic clock to operate in space, and the timekeeping device is so accurate that it will only lose one second in a billion years. The Cold Atomic Clock in Space (Cacs), launched into space yesterday as part of China’s Tiangong-2 space lab, beats the most accurate US atomic clock – a based at the National Institute of Standards and Technology – which loses one second every 300 million years.

“It is the world’s first cold atomic clock to operate in space … it will have military and civilian applications,” Professor Xu Zhen, a scientist involved with the Cacs project, told the South China Morning Post.

Cacs’s accuracy is facilitated by two factors; being a ‘cold’ atomic clock, it uses lasers to slow the speed of the atomic atoms from hundreds of metres per second to one centimetre per second, and being in space those atoms are less influenced by the force of gravity. The European Space Agency has had similar plans for a cold atomic clock in space – the Pharao clock, as part of the Aces project – but its launch has been delayed until next year.

Cacs is not the world’s most accurate atomic clock, though: Physikalisch-Technische Bundesanstalt, based in Germany, has built an experimental timepiece which is two orders of magnitude more accurate than a caesium clock, meaning that it would not lose even a second in a billion years.