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  • Sahil Bade

The Clock That Rules Them All

Clocks are a very useful tool in our lives (duh). But how is time actually measured? And how do entire countries have the same times on all of their clocks? Well, we have an object called an Atomic clock. Sounds fancy right? In this article, I will explain what they are and try to explain how they work.

All clocks keep track of time by counting the ‘ticks’ of a ‘resonator’. For example, in a grandfather clock, the resonator is the pendulum inside it and the gears keep track of the time by counting the ‘resonations’ of the pendulum. This type of pendulum is called a ‘Second’s Pendulum’. You may have, or, will learn about it in the 9th grade. So, an atomic clock basically uses the resonance frequencies of specific atoms as the clock’s resonator.

But why use atomic clocks at all? Surely they are the same! Well, the thing is, they are not. Atoms resonate at so very consistent frequencies, that the accuracy of atomic clocks cannot be matched by any other clock in the entire world (or universe probably)! The newest atomic clock, the National Institute of Standards and Technology (or NIST) F1 uses caesium gas in a fountain arrangement. In a vacuum chamber, caesium gas is introduced. Then, six infrared lasers push the atoms in the gas together to make a ball. By this, the ‘ball’ of atoms is cooled down to temperatures near 0 K, or, absolute zero. Then, two vertical lasers are used to gently push the ball. This launches the ball a meter high into a microwave radiation-filled cavity. During the trip, the atomic state may or may not change when they interact with the radiation. When they come back down, a laser is pointed at them. Any atom whose state was changed by the radiations emits light (called fluorescence). The photons (particles that transmit light) emitted 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 changes the states of most of the caesium atoms and maximizes their fluorescence. This frequency is the natural resonance frequency of the caesium atom (9,192,631,770 Hz), or the frequency used to define the second. So, as per the newest definition, ‘The second is defined by taking the fixed numerical value of the caesium frequency ∆Cs, the unperturbed ground-state hyperfine transition frequency of the caesium 133 atom, to be 9 192 631 770 when expressed in the unit Hz, which is equal to s–1.’

So, in short, caesium oscillates at exactly 9192631770 cycles per second. And since it’s literally an atom, it can never change. Also, the only isotope of caesium that does this is caesium-133, the stable one. All others are radioactive, which means you will literally explode cause the atoms that make you will collide with electrons from the caesium atom and, as put nicely by theoretical physicist Richard Feynman, will ‘jiggle’, and jiggle so much that they will throw out electrons with will make more atoms ‘jiggle’ and repeat the process until you are as dead as a dodo (called beta decay or β-decay).

So you hopefully learned something new - and came to the conclusion that I go on weird tangents all the time.


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