Photo/Illutration A compact optical lattice clock is installed within Tokyo Skytree in 2018. (Asahi Shimbun file photo)

Time moves quicker up on the observation deck of the towering Tokyo Skytree than at ground level, a super-precision clock developed by a University of Tokyo professor shows.

Four nanoseconds faster per day to be exact, quantum electronics professor Hidetoshi Katori and his colleagues found during an experiment at Skytree last spring. One nanosecond is one-billionth of a second.

Katori and his team published their findings in the British scientific journal Nature Photonics on April 7.

The scientists confirmed the phenomenon caused by differing gravity levels at different altitudes using Katori's compact atomic lattice clock, which is still about the size of a household fridge.

Scientists in lab studies previously identified differences between how time passes on GPS satellites and elsewhere in space and at ground level.

But the experiment using the 450-meter-high observation deck of the tower--located in the capital’s Sumida Ward--is the first time the difference has been confirmed with such a high level of accuracy at a commercial facility open to the public. 

Without Katori's custom-made timekeeper, the experiment wouldn't have been possible, as conventional optical lattice clocks are so mammoth in size that just one can fill an entire laboratory.

An optical lattice clock is a type of atomic clock that uses the frequency of atomic oscillation to measure advancement of time.

A myriad of atoms are confined inside Katori's specially designed version. The structure ensures that even after operating for 10 billion years, the clocks won't stray more than 1 second off. The precision level of Katori's clock is more than 100 times that of cesium atomic clocks currently used for time definition.

Katori called the Skytree finding “a major step" toward a wide introduction of the clock in society. 

The scientist foresees a range of potential applications for the timepiece, including using it to monitor tectonic changes stemming from volcanic activity and movements of plates on the seafloor.

“People use clocks to tell the time, but they will become an apparatus to measure time and space, such as the difference in altitude, in line with the theory of relativity,” Katori said.

According to Albert Einstein’s theory, how time advances is affected by the strength of gravity, suggesting that time passes faster at a higher altitude where the gravity is weaker.

The precision level of the Skytree research was as high as that used for surveys conducted on satellites or rockets in space, according to the scientists who carried out the research.

Despite that, the Skytree undertaking still experienced a few unexpected bumps.

The experiment was disrupted by vibrations from trains running nearby and the clock encountered difficulty in cooling due to heating of the space.

But scientists quickly came up with workarounds, installing an improved anti-vibration device and other contraptions on the fly so the experiment could be completed.



 

 

 

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