Why not 1/300,000,000 or something different constant ( why only light ) ?
In: Physics
The metre was originally defined in 1793 as one ten-millionth of the distance from the equator to the North Pole along a great circle, so the Earth’s circumference is approximately 40000 km.
However, that definition didn’t prove exact enough for some scientific work, so we redefined it to be the same length, just using a far more accurate way to measure it.
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