New Values for Natural Constants Available on NIST Web Site

New values for the fundamental constants of nature are now available from the National Institute of Standards and Technology, an agency of the Commerce Department's Technology Administration.

Fundamental constants are the values upon which scientists base descriptions of our universe and theories which describe our natural world. Examples include the speed of light, the gravitational constant and the charge of an electron. The updated values are available from the NIST Web site at http://physics.nist.gov/constants. The international Committee on Data for Science and Technology, also known as CODATA, recently recommended the new values. The constants also will be published in the November/December issue of the Journal of Physical and Chemical Reference Data and in the April 2000 issue of the Reviews of Modern Physics.

"The fundamental constants of nature and closely related precision measurements are truly the common meeting ground for many of the disciplines of science and technology," says NIST physicist Peter J. Mohr, chairman of the CODATA Task Group on Fundamental Constants and co-author of the upcoming paper.

"Fundamental constants are the links between our most basic theories and the physical reality we wish them to describe," says NIST physicist Barry N. Taylor, whose six-year term as chairman of the task group expired at the end of 1998. Taylor, also a co-author of the paper, has been involved with adjustments of the values of the constants for more than 30 years.

Mohr and Taylor spent much of the past four years evaluating experimental measurements and theoretical calculations relevant to the constants from researchers worldwide. They considered all results that were available as of Dec. 31, 1998. The last official CODATA revision to the fundamental constants was issued in 1986.

Mohr and Taylor carried out rigorous reviews of the available measurements and calculations and the uncertainties assigned to each, applying corrections where necessary and conferring with scientists around the world on almost a daily basis. Their evaluation produced values for more than 300 fundamental constants. Upon completion of Mohr and Taylor's review and analysis, the CODATA Task Group concurred that it represented the world's current knowledge of the values of the constants. The task group is a 13-person committee whose members are precision measurement experts from Europe, the United States, Canada, Japan, China and Russia.

While the changes in the recommended values of the fundamental constants are not dramatic—many just have more decimal places—it's the changes in uncertainties assigned to the values that are most noteworthy. Most have been decreased significantly, meaning that scientists are much more confident in their knowledge of the values.

Efforts in the scientific community to establish a single set of international values for the fundamental constants date back to the 1920s. The CODATA Task Group on Fundamental Constants, formed in 1969, published its first set of recommended values of the fundamental constants in 1973. The 1986 set came next.

In addition to Mohr and Taylor, other NIST staff have contributed to the new set of recommended values. One NIST research group, including physicists Richard L. Steiner, Edwin R. Williams and David B. Newell, reported the world's best measurement of the Planck constant in 1998 based on a moving-coil watt-balance experiment. Another NIST research group led by physicist Michael R. Moldover reported the world's best measurement of the molar gas constant in 1988 based on measuring the speed of sound in argon using a spherical acoustic resonator.

"Our support of the CODATA Task Group and our measurement of fundamental constants ensure that scientists worldwide have access to a reliable set of values of the constants to further our understanding of the universe," says Katharine Gebbie, director of the NIST Physics Laboratory.

As a non-regulatory agency of the U.S. Department of Commerce's Technology Administration, NIST strengthens the U.S. economy and improves the quality of life by working with industry to develop and apply technology, measurements and standards through four partnerships: the Measurement and Standards Laboratories, the Manufacturing Extension Partnership, the Advanced Technology Program, and the Baldrige National Quality Program.