Who Decides How Long a Second Is? Exploring the History and Science of Timekeeping

Have you ever wondered who determines the length of a second? You might be surprised to learn that it's not a simple answer. Timekeeping has evolved throughout history, and the way we measure time has changed along with it. In this article, we'll explore the history and science of timekeeping to uncover who decides how long a second is.

The History of Timekeeping

Humans have been measuring time for thousands of years. The earliest timekeeping devices were sundials, which used the position of the sun to tell time. The ancient Egyptians and Babylonians were among the first civilizations to use sundials, and they divided the day into 12 parts. The Greeks and Romans later adopted this system and created the first mechanical clocks.

In the Middle Ages, mechanical clocks became more common, and they were used to regulate the daily lives of monks and other religious communities. These clocks were spring-driven and used a pendulum to regulate their accuracy. However, they were not accurate enough for scientific purposes.

It wasn't until the 17th century that timekeeping became more precise. In 1656, Dutch scientist Christiaan Huygens invented the pendulum clock, which was much more accurate than previous timekeeping devices. This allowed scientists to measure time more precisely and accurately.

In the 18th and 19th centuries, the demand for accurate timekeeping increased as navigation and global trade became more important. This led to the development of marine chronometers, which were highly accurate clocks that could keep time at sea. This allowed sailors to determine their longitude and navigate more accurately.

The Science of Timekeeping

Today, time is measured using atomic clocks, which are incredibly precise. Atomic clocks use the vibrations of atoms to measure time. The most commonly used atomic clock is the caesium atomic clock, which measures the vibrations of caesium atoms.

The length of a second is defined as the duration of 9,192,631,770 periods of radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom. This definition was adopted by the International System of Units (SI) in 1967.

The International System of Units

The International System of Units (SI) is the modern form of the metric system. It is a system of measurement that is used throughout the world and is based on seven base units: the metre, kilogram, second, ampere, kelvin, mole, and candela. These base units are defined by physical constants, such as the speed of light and the Planck constant.

The SI is overseen by the General Conference on Weights and Measures (CGPM), which is responsible for maintaining and updating the system. The CGPM meets every four years to discuss changes to the SI and ensure that it remains relevant and accurate.