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Gold/Mining/Energy : Global Platinum & Gold (GPGI) -- Ignore unavailable to you. Want to Upgrade?

To: d:oug who wrote (12298)	11/14/1999 11:14:00 PM
From: d:oug	Read Replies (1) \| Respond to of 14226

...that counts the jiggles bothers the atoms and contaminates time. Why We Can't Tell What Time It Is By Hannah Holmes Once upon a time, a day consisted of one spin of the Earth, and a second was about an eighty-six-thousandth of that. Things were simple then. Now there are actually two times at any given moment, each notoriously inaccurate, which is highly confusing -- although if you're creative they could provide a fresh excuse for being late for work. "Atomic clocks" have come close to rubbing out old-fashioned time. Nonetheless there are still a few people who use this antiquated day/night version, which goes by the catchy title of "Universal Time," or UT, for short. Admittedly UT can be a chore to use. Because ocean tides, weather and planetary wobbling all affect the Earth's rotation speed, some days are actually longer than others. In addition to slowing down a thousandth of a second per century, the Earth also speeds and slows on a daily, even hourly, basis. One eighty-six-thousandth of today might be longer, or shorter, than an eighty-six-thousandth of tomorrow. Horribly inaccurate. Thank heaven for the International Earth Rotation Service, although its name perhaps overstates its role. The IERS collects and distributes data on all this erratic earthly behavior, so that timekeepers can turn out a new and improved version of old-fashioned time, called UT1. The biggest customers for this brand of time are space or ocean navigators relying on either the stars or the Global Positioning System. "The stars don't move by our clocks," says Collier Smith, a spokesman for the National Institute of Standards and Technology, which keeps time for America. "The stars move, or appear to, according to how the Earth moves." And so everyone using celestial navigation needs a version of time that is related to how fast the whimsical horizon is delivering up new stars. Allegedly a clock that's one second off from UT1 can produce a quarter-mile navigational bungle. But evidently even spiffed-up day/night UT1 time doesn't cut the mustard. Enter the atomic clock. Atomic clocks, which were invented in the 1970s, simply measure the jiggling of dependable atoms such as hydrogen or cesium. These little atoms should jiggle steadily for centuries, the theory goes. Problem is, the apparatus that counts the jiggles bothers the atoms and contaminates time. "In theory if a cesium atom is totally unperturbed -- it's not being bumped by any magnetic fields, there's no light shining on it, nothing's bugging this atom -- then its resonant frequency is going to be stable," says Collier. In practice things are bugging the cesium atom, and its "resonant frequency" changes all the time: jiggling faster. Jiggling slower. Horribly inaccurate. Which is why timekeeping institutions manage vast herds of clocks, locked in special chambers. (The U.S. Naval Observatory has 50.) The timekeepers average the output of their flock, and call that an "interval." (Street name: "One second.") "Coordinated Universal Time" (UTC) is completely abstract -- just loosely wired to the sunrise and patched up with "leap seconds" every year or two when the atomic clocks jiggle too far ahead of the planet. Defective and hurried though it is, the UTC interval is popular. Everyone in the market for really precise time uses it to coordinate essential activities: When you telephone the "time," the cheeps you hear are the progeny of atomic time. When the television news comes on at 6 every night, you're seeing UTC in action. When the check you write clears before the deposit does, you're feeling it. The UTC interval is also reproduced in good clocks. And in not-so-good clocks: The next time you're late meeting your friends for a beer, remember that strapped to your wrist is a sloppy, degraded version of time, coldly divorced from earthly reality. Or better yet, look at your watch, then ask accusingly, "When are you guys switching to UT1? You're always early." Vocabulary Nutation, n. A nodding motion of the rotation axis of a spinning object. Sample sentence: Nancy Kerrigan nutated wildly, then crashed to the ice. Copyright ¸ 1997 Discovery Communications, Inc.