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Kilogram Conflict Resolved at Last

posted by n1 on Thursday October 15 2015, @09:19PM   Printer-friendly
from the about-the-same-as-a-bag-of-sugar dept.

Phoenix666 writes:

For decades, metrologists have strived to retire ‘Le Grand K’ — the platinum and iridium cylinder that for 126 years has defined the kilogram from a high-security vault outside Paris. Now it looks as if they at last have the data needed to replace the cylinder with a definition based on mathematical constants.

The breakthrough comes in time for the kilo­gram to be included in a broader redefinition of units — including the ampere, mole and kelvin — scheduled for 2018. And this week, the International Committee for Weights and Measures (CIPM) will meet in Paris to thrash out the next steps.

“It is an exciting time,” says David Newell, a physicist at the US National Institute of Standards and Technology (NIST) in Gaithersburg, Maryland. “It is the culmination of intense, prolonged efforts worldwide.”

[...] In 2011, the CIPM formally agreed to express the kilogram in terms of Planck’s constant, which relates a particle’s energy to its frequency, and, through E = mc2, to its mass. This means first setting the Planck value using experiments based on the current reference kilogram, and then using that value to define the kilogram. The CIPM’s committee on mass recommends that three independent measurements of Planck’s constant agree, and that two of them use different methods.

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  • (Score: 2) by Thexalon on Friday October 16 2015, @04:33PM

    by Thexalon (636) Subscriber Badge on Friday October 16 2015, @04:33PM (#250634)

    I would think a natural definition would pick a nice round number with few significant figures. Like exactly 1E6 wavelengths of something. I would also be cool with a nice round number like 2^28 (which gives you 9 sig figs in base 10). That would also be arbitrary though, just like picking that orange-red line.

    My point was that the original idea was a nice round number: 1e-7 * 1/4 C where C is the circumference of the Earth. The problem was one of precision, not meaning.

    If you want a completely not-arbitrary system of measurement, try Planck units [wikipedia.org], which are all based around known fundamental constants in the universe like the speed of light in a vacuum. I mean, it's not exactly convenient to represent the distance from where you are to, say, Times Square, in Planck Lengths, but it's at least possible.

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  • (Score: 2) by maxwell demon on Friday October 16 2015, @06:49PM

    by maxwell demon (1608) Subscriber Badge on Friday October 16 2015, @06:49PM (#250751) Journal

    Well, if the units will be defined by the values of the fundamental constants, then it essentially is the same as defining the meter as a certain number of Planck lengths, etc.

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  • (Score: 2) by Alfred on Friday October 16 2015, @07:07PM

    by Alfred (4006) on Friday October 16 2015, @07:07PM (#250767) Journal
    Well done. I think you understand my points better than anyone I have discussed this with. And you have introduced me to Plank units which I shall read about before I do my next arbitrary units rant. Plank units seem a good foil to the arbitrary argument/complaint, you give up a lot of convenience along with the arbitrary.