[Part2]INTERNATIONAL COMPETITION: The ultimate in precision, aiming for a one-second error over 30 billion years

Hidetoshi Katori/photo:Ikuya Tanaka

Hidetoshi Katori is a man on a mission.

The Tokyo University professor is out to make the most accurate clock in the world--a timepiece with a one-second margin of error over 30 billion years.

His Japan-made “optical lattice clock” will continue to measure time accurately for eternity. Its heart is slightly larger than a regular-sized cardboard box, far smaller than might be imagined.

“It might be reduced to the size of a watch one day,” Katori says.

An optical lattice clock defines a second according to the frequency of light projected by a vibrating atom. In principle, this is more or less the same technique used by the cesium-based atomic clock, on which the current international definition of the length of a second is based.

A cesium-based atomic clock loses one second over a period of 30 million years, but Katori is attempting to realize an optical lattice clock a thousand times more accurate that would lose only one second every 30 billion years. The optical lattice clock achieves greater precision by holding 1 million atoms in rows within an optical lattice and measuring their frequencies at once.

Katori presented the principle of his optical lattice clock at an international conference in September 2001. It received a mostly chilly reception, with many doubting that it could be possible. But in 2005, Katori built an actual physical model and proved its effectiveness.

Today, he is gradually coming closer to achieving the goal of a one-second margin of error over 30 billion years that he first mooted 12 years ago.

The inventor's timepiece is a leading candidate to become the new global timekeeping standard for defining the length of a second.

In the past, a second was calculated based on the time it takes for the Earth to make a full revolution on its own axis (one day) and the period of time it took the Earth to orbit the sun (one year). The definition of a second was revised with the advent of the cesium-based atomic clock in 1967. Timekeeping technology has advanced in almost half a century since then, and the International Committee for Weights and Measures is currently considering revising its definitions once again.

In 2001, the committee began seeking candidates for a standard clock that would form the basis for a new definition of a second. There are now eight hopefuls. Apart from the optical lattice method, there is also a single-ion atomic clock that was devised in the 1980s. In addition to Japan, standards organizations from the United States, Britain, France, Germany and elsewhere are also engaged in research.

At present, the single-ion atomic clock from the United States, which has had a head start in terms of its development, is slightly superior in terms of accuracy. Even so, the precision of the optical lattice clock is rapidly improving.

“The optical lattice method can make measurements in a short period of time,” says Feng-lei Hong of the National Institute of Advanced Industrial Science and Technology. “It also has an advantage because many countries, including France and Germany, are working on its development.”

If a clock developed by a particular country becomes the global timekeeping standard, not only will it announce its scientific and technological prowess to the world, it will make it easier to proceed with research and commercial ventures based on the new standard.

“Western nations understand the importance of standardizing time, and they all want to have a part in it,” Hong says.

At present, it looks as if it will be another 10 years before this new definition of a second is decided.

“optical lattice clock”/photo:Ikuya Tanaka

What will happen if this “one-second error over 30 billion years” can be made a reality?

“It will become possible to measure distortions in space and time that previously could not be verified without observing space, and right before our eyes,” Katori says.

According to Albert Einstein's theory of relativity, time slows as gravity intensifies. In other words, the closer you are to the ground, the slower time moves. The difference is extremely small, but Katori says an optical lattice clock can measure how fast time moves in places with elevations that vary by only a few centimeters.

“Our concepts of time and clocks will probably change completely,” he says.

It is said that optical lattice clocks will be able to improve the accuracy of GPS systems and high-volume, high-speed communications. Furthermore, they could also lead to the development of sensors for probing gravitational fields, raising expectations of possible applications in resource exploration and earthquake research.

(The first portion of the article was written by Ikuya Tanaka, senior staff writer of The Asahi Shimbun.)


photo:Shinya Wake

Technology that can control extremely minute units of time called picoseconds (one-trillionth of a second) is supporting cutting-edge science.

At CERN (European Organization for Nuclear Research) in Geneva, experiments are being carried out to examine the phenomenon that occurs immediately after protons collide head-on at high speeds. It is said to resemble the state of the Earth soon after the Big Bang that created the universe 13.7 billion years ago, or in other words, as close as we can get to observing the creation of a tiny cosmos.

The experiments use a giant particle accelerator called the Large Hadron Collider. In a doughnut-shaped pipe 27 kilometers long that runs through an underground tunnel, protons are sent racing around lap after lap until they approach the speed of light and are smashed into each other.

CERN press officer Arnaud Marsollier showed the accelerator's tunnel to The Asahi Shimbun. The accelerator's tunnel is 100 meters below ground where the air is chilly. The tunnel follows a gentle curve, blocking the views of what's ahead. Several bicycles were parked nearby, to be used by workers moving along its impressive length. If one lap is 27 kilometers long, that makes it slightly shorter than the JR's Yamanote train line that circles metropolitan Tokyo.

Two pipes, each 15 centimeters in diameter, stretch through the tunnel at about waist height. Inside them, a proton beam several fractions thinner than a human hair races around at close to the speed of light, then crashes into another beam traveling in the opposite direction. The management of ultraprecise units of time like picoseconds is absolutely essential when accelerating protons.

According to CERN Radio Frequency group leader Erk Jensen, in order to accelerate protons by repeatedly adding energy every billionth of 2.5 seconds, it is vital to accurately grasp the timing with which they enter the accelerating device. If they are even a picosecond off, their acceleration decreases drastically. The timing has to be adjusted precisely by one-trillionth of a second or protons cannot be adequately accelerated.

Time management of this precision is impossible for a human, so computers are exclusively used to make the calculations and adjust the timing.

“The time measurement is an important factor of our experiment, but many people thought it was a secondary factor or only a part of the technical factors we need,” Jensen says. “Now, some scientists pay more attention to the importance of the time measurement and have started studying it more technically.”

In 2011, an incident took place that provided a wake-up call about the importance of precise time management in advanced physics experiments.

During an experiment in which neutrinos launched by CERN were to be caught by a detector in Italy around 730 kilometers away, a neutrino was found that moved faster than the speed of light. The announcement by an international team shocked the world. However, the following year it was discovered that the result was incorrect. A cable linking the clocks for apparatus used in the experiment and external devices on the Italian side were found to have been inadequately connected, which is believed to have caused the error.

At CERN, a new technology that enables highly accurate system time management has begun to be used in some experiments. The project is called “White Rabbit,” after the “Alice in Wonderland” character who leads the protagonist on a journey into a strange realm.

(The second portion of the article was written by Shinya Wake, GLOBE staff writer.)

Translated by The Asahi Shimbun AJW. More related stories available at

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