Optical clocks on Tokyo Skytree prove time passes faster at higher altitude than on ground

A clock at a higher altitude ticks quicker than one at lower altitude,  following Einstein’s theory of general relativity. The latest optical lattice clock research jointly conducted by scientists from Japan has proven that time at the Tokyo Skytree observatory at around 450 meters above sea level passes four nanoseconds (one nanosecond is one-billionth of a second) faster per day than at near ground level.

The world’s first successful development of a portable optical lattice clock with high-precision

The experiment was led by Hidetoshi Katori of government-backed research institute Riken’s Quantum Metrology Laboratory and the University of Tokyo. Using a miniaturized version of optical lattice clock, which can accurately measure a period spanning less than a second by up to 18 decimal figures, the team successfully developed the world’s first portable optical lattice clock with 18-digit accuracy. The clock is extremely precise and it only goes out of synch by one second in 16 billion years. The researchers also made the optical lattice clocks insensitive to temperature changes, vibrations and electromagnetic fields.

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Clocks in a strong gravitational field will tick slower than those in a field with weaker gravity

Placing one of the clocks 450 meters up from ground level on the tower’s observation deck, and another in a meeting room on the first floor with only 3.6 meters up from ground level, the team was able to confirm that each second at the top of Tokyo Skytree passes approximately four in a hundred-trillionths of a second faster, and successfully verified general relativity on the ground. 

The outcome of the research led by Hidetoshi Katori and his team was released on April 6 in the online scientific journal Nature Photonics.

Quantum electronics professor Hidetoshi Katori was awarded Leo Esaki Prize in 2017, to recognize his remarkable achievement in the field of Nano Technology, promotion of Science and Technology, and contribution to the activation of the industry.

Moving experiment to field application in daily life

The team hopes to demonstrate the application of these accurate measurements anywhere outside the laboratory, with transportable devices. This is the first step toward making ultraprecise clocks into real-world devices. The clocks are expected to be used to monitor spatiotemporal changes of geopotential caused by earthquakes or volcanic eruptions which will have an immense impact on future society.

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