By Steve Herman
Man's quest to track time accurately dates back thousands of years. The ancient Egyptians devised the sundial and the water clock. The Babylonians divided the hour and minute into 60 parts, setting the stage for the first mechanical clocks in Europe in the late 13th century. Now, another revolution in high-tech timekeeping is underway.
For generations, the accuracy of timekeeping could be heard in the ticking of the second hand of a handcrafted watch. Swiss horologists in the early 19th Century found a way to build watches that correct for the tiny errors in timekeeping induced by gravity. Chronophiles are still willing to pay up to $100,000 for such a precision mechanical watch, says Norio Hattori-Paris, who presides over the F.P. Journe watch showroom in Tokyo's Aoyama fashion district.
"We have collectors who are insisting that our watches are very accurate to the second, not because their lifestyle depends on that, but because they want the beauty of accurate mechanical watches," he says.
For centuries, one second was defined as the time it took a one-meter rod to swing from side to side as a pendulum.
And, in the 1960s, scientists announced the modern second: the time it took a cesium-133 atom to vibrate 9,192,631,770 times.
That is far more accuracy than most people will ever need, but computer producers need a benchmark like this to carry out such critical tasks as keeping satellites in orbit or ensuring that electronic documents are secure and authentic.
And Hiroyuki Ohno, a computer expert at Japan's National Institute of Information and Communications Technology, explains that for some types of modern-day measurement, accuracy in the one-second range is about as outdated as an Egyptian water clock.
"Only one-second accuracy has almost no meaning," he explains. "It's as the same as for the human being world if the clock only displays [the] year. We cannot use [that] clock. In very high-speed computer communication, the situation is the very same: one microsecond accuracy, or more, may be important."
A microsecond is one one-millionth of a second and scientists hope to produce a clock that is many times as accurate as that.
To keep the computerized world in sync, government-funded stations in the United States, Japan, Germany and Great Britain transmit digital radio time signals at very low frequencies, which can penetrate buildings.
The pulses, these are from one of the two Japanese stations, are picked up by special radio receivers, allowing ultra-precise timekeeping for anyone who can receive the signal.
In 1990, a German company figured out how to put this kind of accuracy into the palm of your hand, or more precisely, on your wrist. But the Junghans Mega One atomic watch needed an antenna in its wristband to work properly.
Japanese developers took the technology a step further, figuring out how to cram the receiver and antenna inside the watch itself.
Despite the relative bulkiness and premium prices of radio-controlled wristwatches compared to their quartz ancestors, sales are brisk.
Etsuro Nakajima, the general manager of Casio Computer's timepiece products research and development center, says Casio sold more than 1.5 million of the new generation atomic watches in Japan in the last fiscal year.
"For us this is a very revolutionary thing," he notes. "The watch had changed from mechanical to quartz a long time ago. And now from quartz to atomic. And we're shipping 50 percent radio controlled watches of all of the watches we sell in Japan."
Yukio Takahashi is a leader of the Japan Standard Time Group at the National Institute of Information and Communications Technology, making him effectively Japan's official timekeeper.
He has 15 cesium clocks in his suburban Tokyo laboratory, which together make up Japan's official master clock. It stays within 50 nanoseconds of Coordinated Universal Time, the world benchmark. That is 50-billionths of one second.
But Mr. Takahashi is still not satisfied, and plans to make his primary clock a thousand times more accurate. "Of course, we must continue to develop the primary clock or Japanese Standard [Time] clock more precisely," he says. "[The] optical primary clock is the next-generation primary clock."
The optical clock will rely on extremely short laser bursts. This timepiece should drift less than one second over 200 million years.
Steve Herman,VOA News, Tokyo.
cesium 铯（金属 ）