Comments by "Kevin Street" (@Kevin_Street) on "How We're Redefining the kg" video.

  1. The basic idea is to redefine all the units of measurement used in SI (the measurement system of science) so they depend upon inherent properties of the universe (physical constants), instead of solid objects. The reason they're doing this is because any solid object will change with time, and measurements based on them won't be accurate forever. (Today's kilogram will weigh a tiny bit less or more than the same kg measured in 1799.) All of the other SI units have already been redefined this way, and now it's the kilogram's turn. By using the method described in the video, the kilogram can now be defined by using two different physical constants: Avogadro's number and the Planck constant. So they're doing two different measurements (one with each constant), and checking to see that both methods agree on the same measurement of the kg. That way they can be certain of the kilogram's weight to a high degree of accuracy.
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  2. Very cool!
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