The time according to atoms
Atomic clocks“An atomic clock is known as such because the way it works is based on the individual properties of atoms”, Thierry Bastin explains. "A pendulum clock is based on the properties of the pendulum but not on the individual properties of the atoms comprising the pendulum. The same is true of quartz clocks based on the oscillation of a quartz crystal, thus on the whole crystal and not on the atoms comprising it. However, in an atomic clock, we use the atoms’ properties individually, even if we use a large number of atoms (1).” How do these clocks work? They are actually improved quartz systems. They do indeed involve a quartz... but one that could be said to be placed under surveillance! By compressing a quartz crystal, oscillating electrical charges appear on its surface; this is how we obtain an electric oscillator (a clock) at a very stable frequency... as long as the dimensions of the quartz crystal don’t change. As we have seen, these possible deformations are of no importance in the majority of applications. But we know that in the long term, a quartz crystal will undergo modifications that won’t be detected. The clock will therefore drift without the user realising it. Atomic clocks allow this defect to be – almost – eliminated since they detect the slightest variations in the quartz’s frequency in real time: we can therefore “recalibrate” it and constantly maintain it at the desired value. (1) Here, it might be useful to remind ourselves that an atomic clock has nothing to do with radioactivity! The chosen atoms aren’t radioactive, there is no phenomenon of disintegration of atoms or emission of particles. Only the size of these clocks and their cost prevents them from being worn on a wrist! |
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