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A clock that measures time to 18 zeros is no small thing

To quote the penultimate riddle from Gollum's challenge to Bilbo Baggins in "The Hobbit": 

This thing all things devours:
Birds, beasts, trees, flowers;
Gnaws iron, bites steel;
Grinds hard stones to meal;
Slays king, ruins town,
And beats high mountain down.

Bilbo got lucky when he asked for more time, given that time was the answer Gollum was looking for, but while time does all those things, we still don’t really understand it.

Scientists at the National Institute of Standards and Technology have gotten a step closer to figuring out time with a new ytterbium-based atomic clock. The new clock is so accurate that the differences in measuring one second to the next would have to be calculated out to the 18th decimal place (a quintillion). That is about 10 times more accurate than any previous atomic clock, including the official cesium-based clock being used today. 

The clock's internal workings are pretty amazing. It has 10,000 rare-earth ytterbium atoms cooled to 10 microkelvin (10 millionths of a degree above absolute zero). The atoms remain trapped in a series of wells made of laser light. A laser ticks 518 trillion times per second to provoke a transition between two energy levels in the atoms. Because there are a lot of atoms, the results can be averaged to become stunningly accurate from second to second.

"The stability of the ytterbium lattice clocks opens the door to a number of exciting practical applications of high-performance timekeeping," NIST physicist and co-author Andrew Ludlow wrote on the NIST website devoted to the new clock. The clocks could have an impact on high-precision sensors measuring gravity, temperature and magnetic field, NIST said.

Another use might be as a rock-solid backup system to navigation. A recent experiment showed how GPS signals could be hijacked or blocked to send ships off course, and there is concern that the same thing could happen to unmanned aerial vehicles, with potentially disastrous results. However, if a GPS signal is compromised, vehicles could fall back onto an inertial navigation system that uses dead reckoning and position data to stay on course. But an inertial system like that requires a small and accurate time piece, such as a chip scale atomic clock. Upgrading portable atomic clocks to ytterbium models would make them even more accurate, if portability were not an issue. The current ytterbium clock, however, is about the size of a dining room table. It also costs $500,000.

Oddly enough, government has only fairly recently gotten into the business of time management, as the American History Guys pointed out in a recent BackStory podcast.  Not all that long ago, each town and city had its own official time, which was based on the position of the sun. So Boston, for instance, was 24 minutes off from Washington, D.C. The problem was that railroads needed to run on set schedules, and trains were often listed as running on whatever time it was in their originating city. A city like Buffalo, N.Y., which had four rail lines, would have five clocks in its station, one for each rail line, and one for the "official" local time. Try catching a train at 2 p.m. in a system like that.

The railroads actually took the initiative to carve up the United States into time zones, in ways that were the least disruptive to their businesses. Railroads were king back then, and the government simply went along with their plan.

Today the government is much more interested in time, as the ytterbium clock proves, but questions still remain. NIST scientists plan to measure the accuracy of the ytterbium clocks (they have the new one and an older model created a few years ago as an experiment) in the near future. One of the questions that still needs to be answered is, believe it or not, what constitutes a true second. I guess Chinese philosopher Lau Tzu was ahead of his time when he observed that "Time is a created thing. To say 'I don't have time,' is like saying, 'I don't want to.'"

I’ll leave it up to the scientists at NIST, or perhaps the railroads, to figure out the remaining mysteries of time. Meanwhile, I'll just sit back and wonder what Bilbo has got in his pocket.

Posted by John Breeden II on Aug 27, 2013 at 9:26 AM


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