NIST and Fundamental Constants

by David Bradley

Dr Barry Taylor of the National Institute of Standards and Technology (NIST) in USA started the meeting with a discussion of the best values of the fundamental constants outlining what they are and the origins of these values and how we have arrived at the best values for this particular period in scientific history. Open any text-book or scientific handbook and one will invariably find lists of constants, explained Taylor, these will include familiar quantities such as the value of the Newtonian constant of gravitation, which is a measure of the strength of gravity, the speed of light in a vacuum, and less familiarly but equally important, numbers such as the mass of the electron and the Planck constant, which describes the size of quanta and plays a central role in quantum mechanics..

Taylor explained how scientists now have available to them a self-consistent set of best values for all the fundamental physical constants, which are applied worldwide by scientists and technologists in every field. These best values are obtained from all the relevant experimental data available at a given point in time. Taylor is a member of CODATA, the Committee on Data for Science and Technology, which brings science up to date with these best values through the scientific literature and more recently through the Web - http://physics.nist.gov/cuu/Constants/index.html. The well-known statistical technique of "least squares" is used to obtain accurate values of the constants from the most reliable experimental measurements and theoretical calculations available.

The most recent exercise was co-authored by Taylor and NIST colleague Peter Mohr under the CODATA Task Group on Fundamental Constants. The current CODATA values are based on pertinent data available as of the end of December 2002 and augmented by selected data that became available by the autumn of 2003, explained Taylor. The CODATA constants cover all fundamental areas of science including, universal, electromagnetic, atomic and nuclear, physico-chemical, adopted values, non-SI units, energy conversion factors, and X-ray values for crystal structure determination studies. The constants are periodically re-evaluated as new experimental techniques push back the boundaries of our understanding. Taylor concluded that such advances will ultimately allow us to give many constants authoritative values by redefining our system of units.

Read on... Theoretical Accuracy of Constants