[Fun Fact] Why the Speed of Light Has No Decimals and the History of the Meter

Have you ever wondered why the speed of light in a vacuum is exactly 299,792,458 m/s? How can such a precise and complicated number have no decimals? To answer this question, we need to dive into the fascinating history of how the meter was defined.

The Origins of the Meter 📏

In 1793, the meter was defined by the International System of Units as exactly one ten-millionth of the distance between the North Pole and the Equator along a meridian. By 1879, this distance was represented using a platinum-iridium alloy bar with marks on each side to denote one meter.

However, there was a problem: this physical bar was stored in the International Bureau of Weights and Measures in Sèvres, France, and not everyone could access it to calibrate instruments. The need for a better, more universal definition was clear.

Redefining the Meter with Waves 🌊

In 1960, scientists decided to redefine some units based on the frequencies and wavelengths of certain radiations. The meter was then set as 1,650,763.73 wavelengths of orange-red light emitted by krypton-86 in a vacuum.

Later, the second was also redefined in 1967, using the frequency of radiation emitted by cesium-133. (Before this, a second was defined as 1/86,400 of a mean solar day, which caused inconsistencies.)

The Modern Definition ⚡

To achieve even greater precision, the definition of the meter changed again: it became the distance light travels in 1/299,792,458 seconds in a vacuum. This was possible because:

  1. The speed of light is constant in a vacuum.
  2. This constancy is supported by Einstein’s special theory of relativity, which postulates that the speed of light does not change based on time, location, or observer movement.

While it may seem counterintuitive, this definition is both logical and universally consistent, as long as we specify that it applies in a vacuum.

Why No Decimals? 🤔

The reason the speed of light has no decimals lies in the fact that our definition of the meter depends on it, not the other way around. Technically, we could have chosen any whole-number value, such as 300,000,000 m/s, but that would have required changing the definition of the meter.

This means the number 299,792,458 m/s isn’t arbitrary—it’s directly tied to the structure of our system of measurements.

Want to Test Your Knowledge? 🌕

Try solving this challenge: The Moon at the Speed of Light. It’ll be a fun and thought-provoking way to explore more about light and measurements!