We have different metrics internationally for length/distance, weights, temperature, etc. Why, as far as I know, is there only hours/minutes/seconds for the entire world? Not that I’m complaining, the alternative would be a huge pain in the a**, but I’m curious how that happened over time (sorry about the pun). TIA!
In: Physics
There is really only seconds. There were old definitions based on the rotation of the Earth, but that’s surprisingly irregular. The standards were set in the CGPM (metric system) back in the 1960s. In 1967 time was one of the first units converted from an object (the spinning earth) to a physical constant = the unperturbed ground-state hyperfine transition frequency of the caesium-133 atom for which 9,192,631,770 oscillations is the definition of 1 second.
Time is also the most accurately measured unit, a paper in Nature described a measuring device with precision of 1.4 parts in 10^18 , or about one billionth of a billionth of a second.
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