Ever wonder how come your alarm clock automatically re-set for daylight savings time? Or how come, when you fly from Atlanta to Chicago, your cell phone "knows" when you land at O'Hare, that it's not in the Eastern Time zone anymore and adjusts the time display to Central Time?
All these devices have a thingy inside that receives signals from The Atomic Clock in Fort Collins, Colorado. Even the humblest $7.99 Wal-Mart or CVS off-the-shelf alarm clock does this. This gizmo in your clock or phone automatically synchronizes to
the radio signal emitted from the U.S. Atomic Clock in Colorado, resetting daily to the split second, and adjusting
automatically to Daylight Savings Time, Leap Year and Time Zone Changes.
It's also the reason you cannot mess with your alarm clock's time setting anymore. You can set the alarm, but whoa unto those who try to re-set the actual time.
So what IS the atomic clock? I'm so glad you asked.
Technical Description
NIST-F1 is referred to as a fountain clock because it uses a
fountain-like movement of atoms to measure frequency and time interval.
First, a gas of cesium atoms is introduced into the clock's vacuum
chamber. Six infrared laser beams then are directed at right angles to
each other at the center of the chamber. The lasers gently push the
cesium atoms together into a ball. In the process of creating this
ball, the lasers slow down the movement of the atoms and cool them to
temperatures near absolute zero.
Two vertical lasers are used to gently toss the ball upward (the
"fountain" action), and then all of the lasers are turned off. This
little push is just enough to loft the ball about a meter high through
a microwave-filled cavity. Under the influence of gravity, the ball
then falls back down through the microwave cavity.
The round trip up and down through the microwave cavity lasts for
about 1 second. During the trip, the atomic states of the atoms might
or might not be altered as they interact with the microwave signal.
When their trip is finished, another laser is pointed at the atoms.
Those atoms whose atomic state were altered by the microwave signal
emit light (a state known as fluorescence). The photons, or the tiny
packets of light that they emit, are measured by a detector.
This process is repeated many times while the microwave signal in
the cavity is tuned to different frequencies. Eventually, a microwave
frequency is found that alters the states of most of the cesium atoms
and maximizes their fluorescence. This frequency is the natural
resonance frequency of the cesium atom (9,192,631,770 Hz), or the
frequency used to define the second.
Geek love. An early iteration of the Atomic Clock, circa 1952
1975 -- NBS-6 begins operation; an outgrowth of NBS-5, it is one of
the world’s most accurate atomic clocks, neither gaining nor losing one
second in 300,000 years.
The Atomic Clock today -- it has an accuracy to about one second in 20 million years
Aren't you glad you asked?