Timekeeping through time – The world has come from keeping time with the Sun and the moon to atoms and their nuclei

Timekeeping through time – The world has come from keeping time with the Sun and the moon to atoms and their nuclei

Subject: Sci

Sec: Nuclear Sector

Context:

Time is an inalienable part of our reality. Scientists don’t understand it fully  at the universe’s largest and smallest scales, but fortunately for humans, a panoply of natural philosophers and inventors have allowed us to keep step with its inexorable march — with clocks.

Clock:

• Clocks are devices that measure the passage of time and display it. Their modern versions have the following parts: power source, resonator, and counter.
• A clock measures the amount of time that has passed by tracking something that happens in repeating fashion, at a fixed frequency.
• The sundials in use in ancient times allowed people to ‘tell’ time by casting shadows of changing lengths against sunlight.
• In water clocks, water would slowly fill a vessel, with its levels at different times indicating how much time had passed. The hourglass served a similar purpose, using sand instead of water.

How did mechanical clocks work?

• Until the Middle Ages, engineers around the world improved the water clock with additional water tanks, gear wheels, pulleys, and even attached musical instruments to the point where they were practically developing rudimentary analog computers.
• One of the first major revolutions in timekeeping that paved the way for modern clocks was the invention of the verge escapement mechanism in the 13th century.
• Combination of mechanical arrangements, could only move in fixed intervals.
• The gear was called an escape wheel if it was circular.
• A second gear, called the balance wheel, enmeshed with the first such that when the escape wheel moved forward one gear tooth at a time, the balance wheel would oscillate back and forth.
• This oscillation would drive the ‘hands’ of a clock on a clockface as long as some force was applied on the balance wheel to keep it moving.
• Using an escapement mechanism, a clock-maker named Giovanni Dondi dell’Orologio built a sophisticated instrument called the ‘Astrarium’ over 16 years in the mid-14th century to track the motion of stars and planets in the sky.
• In the mid-17th century, the Dutch inventor Christiaan Huygens invented the pendulum clock.

How did clocks change shipping?

• The marine chronometer came the next century. For a ship to accurately know where it was on the face of the earth, it needed to know its latitude, longitude, and altitude.
• The latitude could be computed based on the Sun’s position in the sky and the altitude could be assumed to be sea level, leaving the longitude — which requires an accurate clock onboard each vessel.
• Pendulum clocks couldn’t serve this purpose because the ship’s rocking motion rendered them inaccurate.
• A carpenter named John Harrison built a working marine chronometer in 1761 and delivered it to the British government for its longitude prize, worth GBP 20,000 at the time (and more than Rs 21 crore today). This device featured mechanisms that ensured the clock’s operation wasn’t affected by the ship’s rocking, the force of gravity, and some temperature changes.

How do quartz clocks work?

• Two important types of clocks : quartz clock and the atomic clock. The fundamental setup of both these instruments is similar: they have a power source, a resonator, and a counter.
• In quartz clocks, the resonator is a quartz crystal. The power source sends electrical signals to a quartz crystal, whose crystal structure oscillates due to the piezoelectric effect. The signal’s energy can be tuned to make the crystal oscillate at its resonant frequency, making it the resonator. The counter counts the number of periodic oscillations and converts them into seconds (depending on the crystal’s period).

What are atomic clocks?

• Atomic clocks are the most precise clocks made that are true to a billionth of a second. They measure time by tracking the resonant frequency of atoms used in the clock.
• Atoms and electrons in them carry varying energy levels. When an electron gets excited, or gets more energy, it transitions to a different orbit. In the atomic clocks, this is doneby using a certain frequency of electromagnetic radiation which the electron absorbs, thus oscillating the atom. By fine tuning the microwave radiation frequency that can transition multiple atoms to various states, the energy oscillation can be calculated to extremely high accuracy.
• The power source is a laser and the resonator is a group of atoms of the same isotope.
• The laser imparts just enough energy for the atom to jump from its low energy state to a specific higher energy state.
• And when the atom jumps back down, it releases radiation with a well-established frequency.
• An atomic clock made with a caesium atom was the standard measuring unit used to define a second under the universally-used International System of Units (also called SI). This definition of a second is also used in the International Atomic Time (TAI) standard, which a number of synced atomic clocks globally maintain. It is also the basis for the GMT or UTC time systems, which factor in leap seconds and fractions of a second change caused by earth’s rotation.
• Atomic clocks are distinguished by their resonator; each such clock is called a time standard. For example, India’s time standard is a caesium atomic clock at the National Physical Laboratory, New Delhi, which maintains the Indian Standard Time.