![]() ![]() Only the low-energy atoms (the blue line) pass directly into the vacuum cavity where radio waves bombard the atoms. These magnets throw away high-energy cesium atoms by deflecting them outward (as indicated by the red line). Parallel beams emerge from the oven and pass through two non-uniform magnets (see Fig. Nature’s Tiny Pendulumsīut how does one count the number of swings of this atomic pendulum? One sample of cesium is placed in an oven at 100˚ C. 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”. This model is very similar to how vibrating atoms were used to define the length of a second. ![]() 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. Now make that pendulum ‘tick’ more than a billion times from side to side. 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. Consider the following: the purpose of a pendulum in a clock is to keep track of the seconds. In other words, by decreasing the period of the clock, one automatically increases its accuracy. 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'”. 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. ![]()
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