The Big Think

June 3, 2015

The Constant Kilo

Filed under: Science — jasony @ 7:20 pm

I love standards. It’s weird, I know. But there’s something about knowing exactly what something is, to the highest degree of perfection attainable in the universe, that’s just kind of cool to me.

The second is the duration of 9192631770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom.

The metre is the length of the path travelled by light in vacuum during a time interval of 1/299792458 of a second.

The ampere is that constant current which, if maintained in two straight parallel conductors of infinite length, of negligible circular cross-section, and placed 1 m apart in vacuum, would produce between these conductors a force equal to 2×10−7 newton per metre of length.

The kelvin, unit of thermodynamic temperature, is the fraction 1/273.16 of the thermodynamic temperature of the triple point of water.

The candela is the luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 540×1012 Hz and that has a radiant intensity in that direction of 1/683 watt per steradian.

The mole is the amount of substance of a system that contains as many elementary entities as there are atoms in 0.012 kilogram of carbon-12. When the mole is used, the elementary entities must be specified and may be atoms, molecules, ions, electrons, other particles, or specified groups of such particles.

BUT

There’s a problem with the Kilogram. What is the problem? This:

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