Today, I learned about a length unit ‘meter.’
In the past, the meter was defined as one ten-millionth of the distance from the equator to the North Pole, and and a prototype meter was created..
However, the prototype meter had some problems like a lack of invariance.
After that, various definitions were proposed, and in 1986, the problem was eventually resolved.
The new definition of the meter is based on light speed, and it defined as the distance that light travels in 1/299792485 seconds In a vacuum.
There is a possibility that the definition is influenced by the general theory of relativity, but CIPM(International Committee for Weights and Measures) decided that the slight error can be ignored.
