TOWARDS THE PERFECT CLOCK

 

   To measure time, we need some periodic motions. The sun rises and sets regularly. This periodic phenomenon   used to measure time in those days. Sun dial was constructed and the shadow was used to indicate time. We know, the sun's apparent motion is not accurately periodic.

    Then Galileo discovered the pendulum. The time taken by the pendulum for the oscillations does not depend on the mass suspended or the length of the swing but only depends on its length. A "one meter" (99 cm) long pendulum takes 2 seconds for an oscillation. So people constructed pendulum clocks which showed time for 270 years successfully.

   Next came,  quartz crystal based clocks. When a tiny electrical voltage is given to a tiny fork like crystal, perfect vibrations are set in it. Exactly 32768 times a second. This precise frequency is the basis for measuring the second and the time. This electronic clock is definitely more accurate than pendulum and other mechanical clocks.

    We know,sodium lamp (sodium atoms) emit yellow light. The Frequency of yellow light is 5.17*10^14. That is, the sodium atom emits 5.17*10^14 light waves in one second.
Similarly caesium atom emit 9192631770 microwaves in one second. This frequency mostly accurate. So atomic clocks were constructed using caesium. Today "one second" is defined using frequency of waves emitted by caesium atom. Atomic clock is the gold standard for today"s time measurements.

   But physicists say that even atomic clocks are not accurately accurate. Only clocks based on the  Speed of light can be absolutely accurate because the speed of light is fundamental universal constant. And all other physical quantities will at least suffer micro changes in the course of time.

   How to make that"Light Clock".  Take two plane mirrors.keep them parallel at some distance apart.We know, mirrors reflect light rays. Let a light ray travel to and fro between the mirrors. In other words, let light photons bounce and re bounce between the mirrors. This is the periodic motion.
Time taken for to and fro travel by the photons is an absolute constant since the light's velocity is constant. If a clock is built using this concept, that will be the world's perfect clock. That clock will not only measure the time with great precision but will also define the time itself. The "light-clock" is not built so far. but one day, we will make that zero-error clock.