Here's an up-to-the-nanosecond report on time


It seems as though people can hardly sit still anymore without looking at their watches. Even when we're supposed to be enjoying ourselves, like at lunch or the ballgame, arms twist up and eyes glance down.

For what? For the time, of course. As in, we're running out of it.

"Sorry, I don't have the time" has become an all-purpose observation, explanation and excuse in urban America.

And who is responsible? Well, Dennis D. McCarthy says it's not him.

"If we could help, we would. But we don't make it. We measure it," the astronomer shrugs.

Wearing a white shirt and sitting behind a cluttered government desk, McCarthy is America's timekeeper, director of the U.S. Naval Observatory's Directorate of Time.

On his left wrist he wears a Citizen quartz watch that he keeps accurate to one minute by resetting it a couple of times each year. And all the clocks at McCarthy's house, on his VCR, etc., are likewise calibrated to the same minute. Which is, he says, plenty good for everyday.

For more pressing demands, he and a staff of 75 tend to the subtle vibrations of 50-plus atomic clocks spread over the wooded hillsides of the Naval Observatory. These machines keep time to within "billionths of seconds."

Nothing humans can measure can be measured so precisely as time. A billionth of a second is called a nanosecond, the amount of time it takes for light to travel one foot. Neither weight nor distance nor any variable can be measured so precisely, McCarthy is explaining.

And as for the perceived loss of time here at the end of the 20th century, McCarthy professes not only his innocence, but explains that he is doing what he can about it.

Twice each year, according to the ever-so-slight tidal wobble of the Earth's rotation, McCarthy's atomic clocks are subject to possible resetting--to keep his unimaginably accurate timepieces in sync with the less reliable spin of the globe.

In the last quarter-century, the Naval Observatory has added 20 seconds to our calibration of time.

You see, the everyday cliche about our world speeding up is factually untrue. It's slowing down. We are gaining time, no matter what it feels like. The Earth sputters, but clocks don't, and so we gain a second every now and then, at the end of the day on June 30 or Dec. 31.

Alas, this December will pass without us receiving an additional second. McCarthy says the observatory's measurements of the planet's spin show that an extra second is not deserved quite yet.

Oh well, who would have had the time to make use of it anyway?

Keeping time is a $5-million-a-year endeavor here in the rolling forest lands of northwest Washington's embassy district.

But there is a paradox in all this precision. For as accurately as we can measure time, timekeeping turns out to be merely an average--the average of what clocks here say it is. Therefore the need for a good many clocks to improve the average, in this case 50-plus cesium atom and hydrogen maser clocks.

To take matters another step, the United States adheres to a treaty specifying that the official time of the world is maintained outside Paris by the International Bureau of Weights and Measures. America's time counts for 40% of the weighted world average. Atomic clocks in other countries contribute the remaining 60%.

The "how" of timekeeping involves the application of energy to matter. Something like placing your hand on a heated frying pan. The speed it takes you to remove your hand is pretty much constant. Likewise, the movements of energized atoms of hydrogen and cesium are immutable.

Beyond the "how" is the "why."

Why do we need such accuracy?

For one, we need to synchronize colors in the TV signals that stations broadcast. Or target our nuclear missiles. Stock exchanges need computers around the world that are accurate to within seconds, so that no one gets an edge in investments.

The future will make even greater demands. For instance, consider the anti-collision devices now being developed for trains and envisioned for automobiles. These systems, like airline navigation, require knowing at exactly what instant a moving body is where.

To make sure that two approaching trains are on separate tracks requires accuracy of timekeeping of perhaps 10-billionths of a second. To keep motorists from colliding on the freeway might require accuracy of a single nanosecond. No error.

By classic definition, time is the ordering of events. Which suggests a concluding question for McCarthy: If modern timekeeping is the most accurate thing in the history of the world, how come everyone is late these days?


"Well, I could tell you I don't have time to think about that," he says, and laughs. "But a psychologist might tell you that people who are always late are rebelling against time. That might be the case. We've all had it with time."

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