Photo/IllutrationAn optical lattice clock, center, is transported to be set up at the 450-meter-high observation deck of Tokyo Skytree. (Ryo Ikeda)

  • Photo/Illustraion
  • Photo/Illustraion
  • Photo/Illustraion

Under Albert Einstein’s general theory of relativity, time should pass more quickly high up on the 634-meter Tokyo Skytree than at ground level.

That’s the basis of an experiment a group of scientists from the University of Tokyo and other institutes have begun at the observation deck of the tower in the capital’s Sumida Ward, using a super-precision clock made in Japan.

They are testing a mysterious phenomenon that would appear according to Einstein’s landmark 1915 theory.

If the time difference caused by slightly differing gravity levels at different altitudes can be measured precisely, that could lead to the development of technology to accurately estimate the difference in height based on the time lag.

“I want to take the first step toward a paradigm change to measure the height based on the theory of relativity,” said Hidetoshi Katori, 54, an engineering professor at the university.

In the early morning of Oct. 3, workers were carefully transporting equipment about the size of a refrigerator on the observation deck to a room 450 meters above ground level. Its cover was removed there.

The same equipment was also installed in a meeting room on the first floor.

Developed by Katori in 2005, the equipment, one of the world’s most accurate clocks, is known as the optical lattice clock. It is the first time that one has been used outside a lab.

That sort of clock has a precision of 10 to the minus 18 power, which means theoretically that would be less than 1 second off even after operating for 16 billion years--a period longer than the creation of the universe through the present.

Its exceptional level of accuracy is based on the latest laser technology and some experts expect the invention to someday be awarded the Nobel Prize in Physics.

The optical lattice clock uses the frequency of electromagnetic waves that strontium atoms inside generate and absorb instead of a pendulum.

The second hand of an ordinary table clock moves once a second, while most wristwatches’ second hand moves 100 times per second. The larger the number of second hand movements per second, the more precise the clocks are in general.

The optical lattice clock’s frequency is hundreds of trillions of times per second. An atom is trapped in each opening of the optical lattice to prevent many atoms from interrupting each other and affecting the frequency, so a second can be accurately measured.

According to the theory of relativity, time passes more slowly when the gravity is stronger. On Earth, the gravity is slightly weaker and time passes faster at higher altitudes, since those locations are farther from the core of the planet.

Although NASA has measured the time difference between ground level and a place 10,000 kilometers above with another high-precision clock, the altitude difference is much less in the latest project than the NASA experiment.

It would take 700,000 years to generate a time gap of a second between the two points under the Skytree experiment, but the optical lattice clock can detect a very slight time lag that would emerge within only a few days to several months.

Under the plan, measurements will continue for two months and then the data from the two clocks will be analyzed.

The time gap between the observation deck and ground level within a month is estimated at 0.13 microseconds (one microsecond is 1-millionth of a second), according to the researchers.

“I hope people can realize that clocks are faster at high altitudes by setting up the device at such a place (Tokyo Skytree),” said Katori.