Introduction

The atomic clock has revolutionized the 21st century Atlas. What would happen if the Atlas of our time would suddenly shrug? According to Klinkenborg, a writer for Discover magazine, "the Internet would dissolve into an array of freestanding, no-longer-networked computers. ... Trade would abruptly cease on Wall Street, and money and shares would come to rest wherever they were." Jo Ellen Barnett, author of Time's Pendulum, notes that atomic clocks keep the "frequency standard without which our televisions, radios, computers and all our communications systems could not work." It is no understatement to say, as Barnett pointed out, that "modern society is literally held together by electronic technology that routinely communicates by signals synchronized to billionths of a second" (169). While atomic clocks are not an essential element to society's survival, this technology is expanding the limits of telecommunications.

Redefining the Second

Before integrating precise methods of timing into our technology, we first had to define the fundamental unit of time: the second. Initially, the second had been defined as 1/86,400 of a mean solar day, a value obtained by slicing the day into 24 hours, breaking each hour into 60 minutes, and dividing each minute into 60 seconds. With the advent of the atomic clock, a better method of defining the second came into play: instead of breaking up the solar day into smaller and smaller bits, a new "bottom-up definition" came into play where "the day had officially become 86,400 atomic seconds, and the atomic second the single fundamental unit of time" (Barnett 168).

Equally interesting as to how the second is defined is the question of why the second had to be redefined. If we use the solar day to measure the second, we quickly discover by scientific experiments the inadequacy of using the earth as our timekeeper. The problem stems from the erroneous assumption that the earth consistently traces out the same path around the sun. Scientists have evidence that points to how the earth does not run like clockwork; it displays idiosyncrasies such as wobbling about its axis and, like its interstellar neighbors, is "gradually losing energy, slowing down, and spiraling toward the sun" (Barnett 166). The idea here is that the distance between the sun and earth is decreasing very slowly over time.

Understanding how the old definition of the second proved to be inadequate in carrying out accurate measurements gives us motivation to find a better mechanism to measure time. According to Thomas Udem of the Max Planck Institute for Quantum Optics in Garching, Germany, to better the accuracy of a clock one needs to "increase the rate at which it 'ticks'" (Marks 186: 29). In other words, by decreasing the period of the clock, one automatically increases its accuracy. Consider the following: the purpose of a pendulum in a clock is to keep track of the seconds. Imagine taking that pendulum and swinging it faster and faster from side to side, thus decreasing the period, or the amount of time it takes for the pendulum to swing from one side to the other. Now make that pendulum 'tick' more than a billion times from side to side. If you were to compare this altered pendulum rate with that of a regular pendulum clock, you would be able to define a second in the regular pendulum clock by the number of times the former pendulum swung side to side within that second. This model is very similar to how vibrating atoms were used to define the length of a second. In the 1967 General Conference of Weights and Measures, this very method was used to define the length of the second as the "duration of 9,192,631,770 cycles of microwave light absorbed or emitted by the hyperfine transition of Cesium-133 atoms in their ground state undisturbed by external fields" (Breakiron).

Nature's Tiny Pendulums

Before we understand specifically how we can harness the vibrations of a Cesium atom to accurately define the length of a second, we must take a look into the nature of atoms. What makes atomic clocks so special is how the atom can resonate at the exact same frequency whether it is here in the US or halfway around the world or in outer space. Identical atoms will emit and absorb the same frequency that changes their state; they share the same properties. Try comparing two mechanical clocks or two quartz clocks in different locations and you won't get that kind of precision. The beauty of atomic clocks resides in their ability to act as near ideal pendulums. No friction, no aging, no distortion, and no running down - the atom proves to be the best known timekeeper.

Although it is the best known timekeeper, it is not a perfect timekeeper. An atomic clock's precision can be tampered with if one allows external magnetic fields or electromagnetic radiation to interfere with the atoms. Even atoms bumping into each other contributes to a slight decrease in the accuracy of the clock. To get a near ideal pendulum, you need to screen out as many external influences as possible.