Chapter II: Length – From Cubits to Kilometers
In ancient times, human beings turned to their bodies as the yardstick for the world around them. The breadth of a hand, the length of a foot, and the span of an outstretched arm were the instruments our ancestors used to measure their world. And so, our journey begins with a “cubit“, a unit as old as civilization.
The Cubit
Emerging from the river valleys of Egypt around 3000 BCE, a cubit was defined as the length from the elbow to the tip of the middle finger. As universal as the human body may seem, there was a challenge – not all elbows to fingertips are equal. The royal cubit, a standard measure used in construction, included the palm’s breadth added to the cubit, making it slightly longer. Even with this early attempt at standardization, the cubit length varied widely across different cultures and periods, ranging from about 444 mm to 529.2 mm.
The Mile
Fast-forward a few millennia to the Roman Empire, which gave us the “mile”. Stemming from the Latin word “mille”, meaning “thousand”, a mile was initially defined as a thousand paces, with a pace being five Roman feet. However, the interpretation of what constituted a foot varied widely, making the Roman mile anything but standard.
The French Revolution
The journey of defining length took a crucial turn during the French Revolution when the metric system was born. The “meter“, a word derived from the Greek “metron”, meaning “a measure”, was conceived to be one ten-millionth of the distance from the North Pole to the Equator. Later, this was refined as the distance between two engraved lines on a platinum-iridium bar was kept at the International Bureau of Weights and Measures near Paris. Today, the meter is defined in relation to the speed of light, making it not just a measure of space but intrinsically linked to time.
Meter’s Definition
In 1983, the General Conference on Weights and Measures (CGPM), an international body that oversees the global system of measurements, defined the meter in terms of the speed of light.
According to the new definition, a meter is a distance that light travels in a vacuum in 1/299,792,458 of a second. This definition was adopted to increase the precision with which the meter could be measured.
So essentially, the speed of light is now a fundamental constant of nature used to define the meter. The speed of light in a vacuum is exactly 299,792,458 meters per second. This decision made the meter more accurately measurable and universally applicable in scientific research.
This reflects a broader trend in metrology (the science of measurement) toward defining units with respect to fundamental physical constants, as these are universally accessible and not subject to change over time or space.
Today
Yet, even in the 21st century, the world isn’t wholly metric. The United States, Liberia, and Myanmar continue to use the Customary system, measuring length in inches, feet, yards, and miles. And even within these countries, the metric system permeates science, medicine, and the military.
Despite the differences and the long road to standardization, the measure of length, whether a cubit, a foot, or a meter, continues to be a crucial scaffold upon which we construct our understanding of the world. The length story is one of human innovation and adaptation, which mirrors our growth. From measuring the land for farming with our forearms to navigating vast oceans and charting the endless expanse of space, our concept and measure of length have come a long way. But the journey is far from over, as our reach extends from the ocean’s depths to the farthest galaxies.
