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Time Keeps Beating... To The Cycle Of An Atom
by Reg Atley
http://www.atomicclocku.com
So you want an atomic clock? They are the most accurate
form of time keeping out there, and even have a space age
name. But what exactly are they, and how much should we
pay for one? While we are at it, are they actually worth
the money?
Atomic clocks are not really so different from any other
kind of clock. At the heart of a clock there needs to be
something that taps out a really regular rhythm. Then this
beat is turned mechanically or digitally into a time we can
understand. It doesn't really matter how rapid the beat
is, as long as it is regular, but a pendulum clock is set
up to tick and tock every second. These old-fashioned
clocks are pretty accurate, as long as you remember to keep
them wound - a good grandfather clock can be accurate to
half a second a day.
Sources used for keeping time have expanded past the source
used for pendulum clock, which incidentally was first
planned by Galileo but never made by the man himself. One
example of a modern use of science in clock technology is
quartz, which is often used in today's digital watches.
When a small electrical current touches quartz, the quartz
vibrates at a relatively reliable frequency. Several modern
clocks and watches take their cue from quartz and are able
to keep time at an accuracy of one-10th of a second each
day.
This level of accuracy is all most people really need in a
timepiece. After all, who really has to use an extra tenth
of a second when you have 86,400 other seconds to use each
day? Basically, the average person can get by with this
level of accuracy. Still, other people need a much more
accurate timepiece, especially those in the field of science
and navigation. These fields inspired the creation of the
atomic clock. This clock is immensely accurate.
In fact there is an atomic clock sitting in the offices of
the National Institute for Standard and Technology that
looses only thirty billionths of a second each year! No
excuse to be late for a meeting if you work for those guys.
It works by picking a rhythmic source that is hugely
predictable and accurate. It is cesium, an element with a
very fast but never changing resonant frequency. If you
are interested the formal definition of a second
(established in 1967) is nine billion one hundred and
ninety two million six hundred and thirty one thousand
seven hundred and seventy cycles of a cesium atom...
The NIST's clock is a high end model, and there are
different versions available. But you are unlikely to
ever want to buy one since even a hand held version will
probably set you back twenty thousand dollars. So what are
those things we've all seen advertised for twenty bucks?
The atomic alarm clocks and watches that are so easy to buy
are not themselves atomic clocks. Instead they contact an
atomic clock by radio and automatically update from that
source. This means that you are getting the benefit of
atomic clock accuracy for the price of a standard clock.
All this is academic to most of us, who do not need or want
such accuracy. But these clocks that update from the
atomic clock have one big advantage - you never need to
fiddle about setting them! For this reason alone, many
people find them worth the asking price.
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