Meeting Information

The Planck Constant and the Redefinition of the SI

September 19, 2012
American Center for Physics
College Park, MD

Date: Wednesday, September 19, 2012

Speaker: Stephan Schlamminger, University of Washington and NIST

Topic: The Planck Constant and the Redefinition of the SI format_pdf

Time and Location: 1:00 PM, with Q&A to follow; in a 1st floor conference room at the American Center for Physics, 1 Physics Ellipse, College Park, MD-- off River Rd., between Kenilworth Ave. and Paint Branch Parkway.

Abstract: In 2011 the General Conference on Weights and Measures (CGPM) approved a resolution entitled “On the possible future revision of the International Systems of Units, the SI.” The adoption of this resolution is an important step in the process of moving the SI from an artifact based system to a fundamental constant based system. With the approval of the resolution, a revision of the SI system could be made in as early as four years.

This revision will change the definition of the SI from seven base units to seven fundamental reference constants. For example the meter will be realized using the speed of light, the kilogram using the Planck constant. In the new SI, all units will be truly universal, i.e., can be realized everywhere in the universe without needing artifacts that are kept near Paris.

In this presentation, I will discuss the SI system with an emphasis on the kilogram and correspondingly the Planck constant. At NIST the Planck constant is currently measured using a device called watt balance, which essentially compares mechanical power to electrical power with a high precision. I will explain the fundamental principle of the watt balance and show recent measurements. I will further share the design of the next generation watt balance, currently under construction at NIST with the purpose to realize the kilogram after redefinition.

Biography: Stephan Schlamminger received a diploma in physics from the University Regensburg, Germany in 1996. He earned his PhD from the University Zurich, Switzerland working on a precise measurement of the gravitational constant using a beam balance. In 2003 Stephan joined the University of Washington in Seattle, WA as a post-doc and was promoted later to a Research Assistant Professor. During this time, he worked on tests of the equivalence principle and noise measurements for the planned space based gravitational wave detector LISA, as well as the existing gravitational wave observatories, LIGO. Since 2010 Stephan Schlamminger is on detail to NIST, where he started designing the next generation watt balance.

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