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Phoenix666 writes:

Fundamental constants are physical quantities that are universal in nature.
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According to a recent evaluation and update of the values of the fundamental constants by researchers at the National Institute of Standards and Technology (NIST), the uncertainties in measurements of the constants have now been reduced to such exceedingly low levels that all of the SI units can now be linked to them.
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The latest update of the values of the fundamental constants was authored by NIST's Peter Mohr, David Newell and Barry Taylor, who lead the international Task Group on Fundamental Constants of the Committee on Data for Science and Technology (CODATA). This task group updates the values every four years. The new quantities represent the latest comprehensive adjustment of values of the constants. In the summer of 2017, the task group will perform a special update to produce the final values for four fundamental constants to be adopted in the fall of 2018 by an international body known as the General Conference on Weights and Measures (Conférence Générale des Poids et Mesures, or CGPM).
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Examples of fundamental constants range from the magnitude of the elementary charge of a single electron or proton to the extraordinary number of particles in one mole of a substance, described by the Avogadro constant. Another example is the Planck constant, a quantity at the heart of quantum physics that will be used to redefine the kilogram as an invariant property of nature instead of a standard platinum-iridium cylinder.

The evaluation and update reduce the uncertainties in both the Planck and Avogadro constants by almost four times compared to the previous evaluation, to just 12 parts per billion. These uncertainties decreased by reconciling measurements in different "watt-balance" devices around the world and new highly accurate X-ray measurements of a softball-sized sphere of silicon that is a nearly perfect crystal and is made almost entirely of the same isotope of silicon (99.9995 percent silicon-28). The update reduces the relative uncertainty by almost two times, to 0.6 parts per million, for the Boltzmann constant, which can be used to determine the amount of energy in a gas at a certain temperature.

Related reporting.

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