What makes the speed of light exactly 299,792,458 metres per second?

1 Answer
George C. ยท Azhar A.
May 25, 2016

The definition of the metre.

Explanation:

The metre used to be defined as the length of a particular International Prototype Metre - a metal bar made from an alloy of platinum and iridium, measured at the melting point of ice.

In 1960, the standard was changed to be expressed in terms of wavelengths of the red-orange spectral line of Krypton-86.

In 1983, the definition was updated to be exactly 1299792458 the distance travelled by light in vacuum in one second.

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