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It’s About Time : Atomic Clocks Take Accuracy to Nth Degree

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Times Staff Writer

Every few weeks, two employees of the U.S. Naval Observatory board a commercial airliner as escorts for an internationally well-traveled and most punctual chap whose ticket is made out in the name Mr. C. Clock.

A super-accurate cesium, or atomic, timepiece, the 150-pound Mr. Clock, who looks much like a suitcase with a digital-watch readout, is strapped into a first-class seat and flown around the world--where his task is to check on the settings of other atomic clocks.

Yes, time does fly, and it is part of the Navy’s incredible effort to calibrate and keep the nation’s time down to the billionth of a second--and sometimes even more accurately than that.

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Many Depend on Precision

And this is no idle exercise in pointless precision: Nuclear submarine navigation, oil field exploration, color television transmission and a number of other important elements of the modern world depend on timekeeping so accurate as to be breathtaking.

While poets and linguists struggle, as they have for centuries, to define this abstract notion of time, scientists here and elsewhere have made it the most precisely measured and calibrated phenomenon in the world. Indeed, the clocks maintained by the Navy are a million times more regular than the creaky old Earth whose diurnal rollings they chronicle.

Up to the Picosecond

Rotations of the globe, after all, can vary by one thousandth of a second a day, on top of which the spinning is slowing down gradually. Some quartz wristwatches are only slightly less accurate than this.

But the clocks on the sprawling green grounds of the Naval Observatory, which the Navy shares with the residence of the Vice President along Washington’s Embassy Row, can chop time down to a “picosecond”--a measurement so refined that an object streaking at the speed of light--186,000 miles a second--would travel only the width of this letter “i” in that amount of time.

Because these clocks have outstripped the performance of the solar system, every 18 months to two years they have to be reset. Usually, this means that the 86,400 seconds of a regular day are extended by a so-called “leap second” to make up for the slowing of the Earth’s rotation.

Yet the keeper of the nation’s time, Dr. Gernot M. R. Winkler, wears a watch--a $12 digital--only when he travels. Otherwise, he says with a smile, “There is no need for me to wear a clock. I get up early, and I’m here two hours before everyone else.”

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Actually, Winkler, an Austrian-born physicist and astronomer, worries deeply about the country’s slavish addiction to regimen. He blames it for everything from “red-light runners” on the streets to dinner guests who seem to insist upon arriving late and proclaiming themselves stylish.

“Our life is paced precisely. The clock is the machine par excellence . The clock is the symbol of precision,” Winkler explains slowly, with a pronounced Austrian clip. “But I belong to the next culture. Time is something for machines, not people. We are not now on the road to greater happiness.”

Winkler, however, cannot escape his 19-year laboratory discipline to getting the most out of a timepiece. So he has advice for those who wear watches and want the greatest accuracy: “Tell them to wear their watch on their bellies. There is much better temperature control, and temperature is an important variable in the working of a clock.”

Clock Readings Averaged

Official timekeeping for the United States and the world is not the job of a single clock, but of dozens of the best timepieces ever built, located throughout the industrialized nations.

The Naval Observatory contributes more than any other organization to these readings, which in total become UTC, or Universal Coordinated Time, maintained in Paris as the standard of the world.

For its part, the Naval Observatory operates about 50 atomic clocks, many of them in climate-controlled vaults in Washington and other locations as a safeguard against an attack on the capital. (Despite their atomic designation, the clocks are not radioactive.)

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They include cesium clocks, in which the oscillations of an energized cesium atom are so unvarying that they define the very standard measure of a second, and Hydrogen Maser clocks, in which the internal rhythms of the simplest atom set a short-term accuracy that surpasses even cesium.

So why put Mr. C. Clock on the road?

In the late 1950s and early 1960s, the answer was that clocks had become so refined that the standard measure of time could no longer be sent electronically. The interval it took to send electrical impulses over long distances was too inaccurate. (It takes 12 billionths of a second, for instance, for an electrical impulse to travel through a 6-foot cord.) So a traveling clock carried the time from laboratory to laboratory.

Stationary Satellites Used

These days, the role of the traveling clock is changed. Satellites positioned precisely in the sky permit the official time to be beamed to clocks everywhere. Because the distance from Earth to a satellite is known to within inches, the time needed to send impulses from one clock to a satellite and back down to another clock can be factored out.

That leaves human error.

When the last “leap second” was ordered to keep clocks in time with the Earth, Winkler recalled, several clock keepers got it incongruously wrong. Somebody, somewhere is bound to misunderstand whether the clock is being moved forward or backward, Winkler said with a shrug.

“Our collective technological abilities have outstripped our individual intellectual capabilities,” he said wryly.

Mr. C. Clock, then, is used to verify time with clocks in other locations--a kind of mechanical safety watching over the work of human timekeepers.

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But the traveling clock seems destined to go the way of the sundial and the sand-filled hourglass. Already there is a small exhibit on the traveling clock at the Smithsonian Institution’s Museum of American History, complete with a copy of one of his airline tickets. After his last flight, some months or years ahead, Mr. C. Clock will have become the victim of still greater demands for precision in time.

Indeed, this seems certain because of the growing sophistication of satellite communication, and because traveling at jet speeds at high altitude affects the time of a clock in tiny billionths of seconds, and errors as large as three billionths of a second can creep into the clock as the result of the transcontinental trips.

Slowly Running Down

The traveling clock, it seems, just cannot keep up with the times.

But the duties of the timekeepers at the observatory remain. Most important, at least among the unclassified responsibilities, is providing the precise time for a system of navigation satellites called the Global Positioning System.

So accurate is this electronic network, Winkler said, that oil explorers can locate a spot where they want to drill to within a few inches anywhere on land. And on the open sea, a Navy helmsman should be able to navigate a battleship through dense fog so closely alongside another ship that crewmen could jump back and forth between them, if you forget about the effect of waves or current.

Television signals, so that colors remain true and stations in one city do not interfere with stations in another, rely on time at accuracy levels that can be delivered best by atomic clocks.

The same is now true of virtually all high-speed communications systems in which enormous amounts of data are sent and received at precise intervals--and, of the recorded time message from the phone company.

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For conformity and coordination, all these systems are based on the time kept by the government, both by the Navy in Washington and by the U.S. Bureau of Standards in Colorado, which maintains its own atomic clocks and also broadcasts a radio time signal.

All of this is a far cry from just a century ago, when each community kept its own time and decreed that noon was simply when the sun was directly overhead. An 1869 conversion schedule shows the difficulty with this: When it was exactly noon in Washington, it was 8:58 a.m. and 25 seconds in San Francisco, and 9:02 a.m. and 21 seconds a few miles inland at Sacramento, and it was 12:12 p.m. plus 12 seconds in New York City.

Views of Time’s Meaning

But for all the scientific progress in the refinement of time, Winkler, as thousands of people before him, still ponders how to define it.

“Time is a symbol for change,” Winkler says. Indeed, he adds, “It is an invention to save time,” by bringing order to affairs so that a family can get its children to school, conduct commerce, use transit carriers and obtain seating at restaurants on a common schedule.

“It really represents the basis for all civilized life in our modern world,” Winkler concludes.

Perhaps few of these modern matters concerned Sophocles in the 4th Century BC, when he pondered time and declared simply, “Time eases all things.”

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Three hundred years later, the Roman poet Ovid had a darker view: “Time, the devourer of all things.” Shakespeare struggled with the concept and announced, “There’s a time for all things.”

In 1748, Benjamin Franklin unleashed the tide of U.S. entrepreneurship with the exhortation, “Remember that time is money.” By 1957, British historian Cyril Parkinson took us from enterprise to bureaucracy with his Parkinson’s law: that time was something that work expanded to fill.

And finally, there is the old saying, probably as good as any: “Time is nature’s way of making sure that things don’t all happen at once.”

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