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.
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