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DTSTART;TZID=America/Los_Angeles:20180315T160000
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UID:727-1521129600-1521133200@rpm.physics.lbl.gov
SUMMARY:Peter Mohr (NIST) "The New SI and Fundamental Constants"
DESCRIPTION:The International System of Units (SI) is expected to undergo a revolutionary change on\nMay 20\, 2019. In October 2017\, the International Committee on Weights and Measures met\nat the International Bureau of Weights and Measures near Paris and recommended a new\ndefinition of the SI such that a particular set of constants would have certain values when\nexpressed in the new SI units. In particular\, the new SI would be defined by the statement:\nThe International System of Units\, the SI\, is the system of units in which \n\nthe unperturbed ground state hyperfine splitting frequency of the\ncaesium 133 atom Cs is 9 192 631 770 Hz\,\nthe speed of light in vacuum c is 299 792 458 m/s\,\nthe Planck constant h is 6.626 070 15× 10−34 J/Hz\,\nthe elementary charge e is 1.602 176 634×10−19 C\,\nthe Boltzmann constant k is 1.380 649×10−23 J/K\,\nthe Avogadro constant NA is 6.022 140 76×1023 mol−1\,\nthe luminous efficacy Kcd of monochromatic radiation of frequency 540×1012 hertz is 683 lm/W\n\nThe numerical values of the constants were determined by a special CODATA adjustment of\nthe values of the constants using data in papers that were accepted for publication by July\n1\, 2017.\nThe Convention of the Meter (Convention du M`etre)\, a treaty that specifies international\nagreement on how units are defined\, was established in 1875 with 17 nations initially signing\non\, including the U.S. The SI\, established within the treaty in 1960\, is more recent and\ncontinues to evolve. Currently\, the treaty is agreed to by fifty-eight Member States\, including\nall the major industrialized countries. Even though a majority of people in the U.S. still\nuse units such as inches and pounds\, the official standards for these units are based on the\nSI units\, so the U.S. national measurement standards will also be redefined\, although the\nchange will be imperceptible in every-day use.\nThe redefinition will have a significant impact on the fundamental constants when ex-\npressed in SI units. Not only will the defining constants be exact\, but many others will also\nbe exact\, and still others will have considerably reduced uncertainties. This reflects a shift\nfrom macroscopic measurement standards to quantum based standards.\nThis talk will describe the new SI\, review reasons for the change\, and show how units\ncan be based on assigned values of certain physical constants.
URL:https://rpm.physics.lbl.gov/event/peter-mohr-nist-the-new-si-and-fundamental-constants/
LOCATION:50-Auditorium
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