A Matter of Time

The Age of The Atom: reaching perfect time

“Life is a constant oscillation between the sharp horns of dilemmas.” H.L. Mencken

We are currently living in the age of atomic time. This is the culmination of a dream of countless astronomers and scientists—to finally be able to keep track of time “perfectly.” Even thought it’s known and accepted that we can now measure time to a minute fraction of a second, it is also known and accepted that the earth neither rotates on its axis nor about the sun in a constant manner.  Because of the latter, we will always have to adjust our time to agree with the earth’s movements no matter how accurate we can measure time. Otherwise, as we have discussed in previous articles, our calendars and seasons will eventually be off.  So the question can be posed: could it be that time as it is recorded now is too perfect?

The question “what time is it?”can no longer be answered by looking to the sky.  Some like to whimsically say that time is the way we divide up eternity or that time is what you experience while beach sand flows through your fingers. But if it’s a time standard you are looking for, the new home for the time standard in the United States is the US Naval Observatory in Washington, DC. When the USNO opened in 1830, its main purpose was to keep track of most of the Navy’s navigational tools. It has since become the government’s source of precise time (USNO), supplying accurate time to the government and all branches of the service via the Department of Defense.  It is also the center for tracking all GPS systems worldwide. Currently, USNO utilizes 61 atomic clocks, among other things, to keep its time keeping precise.  Watching time this closely is important because modern electronic systems depend on precise time to work properly. For example, LORAN navigational systems and GPS systems would position a body 10 feet off its mark for every 10 one-billionths of a second your time was off by.

Atomic clocks are not named because they are powered by atomic energy but because they use certain properties of atoms that can be measured precisely and then used to define time. Time is literally being measured based upon the behavior of the atoms of a given element. Today precise time, currently the most accurate way possible to measure time, is calculated according to the oscillations of the cesium-133 atom.  Though all atoms oscillate or vibrate, some do so more regularly than others. The first atomic clock, based upon ammonia, was built in 1949.  However, it soon became apparent that the cesium-133 atom oscillated more frequently (9,192,631,770 times per second) and more regularly than an ammonium molecule so atomic clocks began to be built in 1952 around the cesium atom.  In 1967 the World’s Conference on Weights and Measures decreed that the world standard for measuring the second would now be based on the vibrations of the cesium atom.  The atomic clocks built in 1967 were 1 second off every 1.4 million years.  The atomic clocks being built in 1999 were 1 second off every 20 million years. It is also worth noting that though the use of anything besides cesium may not be internationally recognized, atomic clocks can also be built using hydrogen or other elements that may perhaps lower the overall cost.

Two of our most current time standards (TAI and UTC) are derived from this atomic system of measurement. Right now the Bureau International des Poids et Measures is in charge of keeping both of these atomic time scales as accurate as possible by keeping them closely inline with the cesium based SI unit of the second. SI is an abbreviation for the International System of Units, which maintains the standards for time (second), and many other measurements including length (meter) and mass (kilogram).

The International Atomic Time (TAI) is the first of these two time standards. It is based upon information gathered from observing cesium oscillate in hundreds of clocks at the same moment in time in laboratories worldwide.  This information is funneled to a central location where it is compiled and used to regulate the passing of time down to the nanosecond. Since TAI is so uniform and unwavering, it does not account for the variations in the rotation of the earth. Therefore Universal Time (UTC), which is the second time standard and the one commonly adhered to by civilians throughout the world, has been derived from International Atomic Time (TAI). What makes Universal Time (UTC) different is the inclusion of leap seconds, which allow atomic time to make adjustments to its otherwise constant rate for the sake of alignment with the earth’s rotation on its axis and about the sun.

In 2002, the United States National Institute of Standards and Technology (NIST) built a clock that would not be off by more than 30 billionths of a second for the entire year. This was possible due to the fountain principle, named for the fountain like motion of the cesium atoms involved. It was applied for the first time to the NIST-F1 atomic clock in Colorado. This NIST clock is among one of the most accurate in the world, with a fault so low that the clock would not gain or lose more than a second every sixty million years.  Now you can clearly see why, even though the flaws in the earth’s rotations are relatively small from our perspective, adjustments to the way we present time to the public are needed to accommodate for these natural flaws.

There are over sixty institutions worldwide like NIST, all striving to develop a timekeeping device that is 100% accurate.  Together, the United States, France, countries that hold national laboratories for the study of time measurement, and all countries that adhere to UTC, are forming a bond to make this dream become a reality. If we all work together, maybe the homeowner will soon have clocks that automatically adjust for daylight savings time and automatically adjust to 100% accurate atomic clocks through radio waves.  The strides we have made in the last 50 years have been monumental. Who knows what the next 50 years will bring.

Back to top ^