How the "meter" came to be one meter long

12 days ago

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Measurement standards are essential for quantifying 'how much' of something exists.
Early distance standards like 'cubits' or 'feet' were based on human body parts.
A 'pace' was commonly used, roughly equivalent to one yard or meter.
The concept of a 'standard meter' originated from observations of pendulum swings.
A pendulum's period is determined by its length and gravitational acceleration.
A seconds pendulum, with each half-swing lasting one second, requires a one-meter length.
Gravity varies slightly across Earth, making pendulum-based length standards non-universal.
In 1790, the meter was defined as 1/10,000,000th the distance from the North Pole to the equator.
This definition was later cast into a platinum bar, serving as a physical standard.
Platinum-iridium alloys with X-shapes were introduced to resist distortions.
In the 1920s, atomic interferometry based on light's wavelength replaced physical bars.
The meter was redefined using wavelengths of light from specific atomic transitions.
In 1983, the meter was defined as the distance light travels in 1/299,792,458th of a second.
The speed of light in a vacuum is constant, making this definition universal.

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