Definition of the Meter by the 17th General Conference on Weights and Measures

On October 21, 1983, a significant milestone in the field of metrology was achieved during the 17th General Conference on Weights and Measures (CGPM) held in Paris, France. The conference redefined the meter, the fundamental unit of length in the International System of Units (SI), based on the constant speed of light.

Background

The meter has undergone several redefinitions since its inception. Initially, it was defined in 1791 as one ten-millionth of the distance from the equator to the North Pole along a meridian through Paris. In 1889, it was redefined as the distance between two marks on a platinum-iridium bar stored in Sèvres, France. As scientific understanding and technology advanced, the need for a more precise and universally accessible definition became apparent.

The 1983 Redefinition

The 1983 redefinition was a result of advancements in laser technology and the precise measurement of the speed of light. The CGPM adopted the definition of the meter as the distance light travels in a vacuum in ¹⁄₂₉₉,792,458 of a second. This definition is based on the fixed numerical value of the speed of light, which is exactly 299,792,458 meters per second.

Key Points

• Speed of Light: The speed of light in a vacuum is a fundamental constant of nature and is invariant, making it an ideal basis for defining the meter.
• Precision and Universality: This definition allows for a high degree of precision and can be reproduced anywhere in the world using appropriate technology, such as laser interferometry.
• Impact on Science and Technology: The redefinition has profound implications for scientific research, engineering, and technology, enabling more accurate measurements and standardization across various fields.

Aftermath and Significance

The 1983 redefinition of the meter marked a shift towards defining units based on fundamental constants rather than physical artifacts. This approach enhances the precision and reliability of measurements, which is crucial for scientific progress and technological development. It also paved the way for future redefinitions of other SI units, such as the kilogram, which was redefined in 2019 based on the Planck constant.

In summary, the redefinition of the meter in 1983 was a pivotal moment in the history of metrology, reflecting the ongoing evolution of measurement standards to meet the demands of modern science and technology.