NOTICE: The project that is the subject of this report was approved by the Governing Board of the National Research Council, whose members are drawn from the councils of the National Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine. The members of the committee responsible for the report were chosen for their special competences and with regard for appropriate balance.

This project was supported by the National Science Foundation under Grant PHY 98-12262 and the Department of Energy under Contract No. DE-FG02-94ER-14451.

Cover: NIST physicist Kris Helmerson looks at a cloud of laser-cooled sodium atoms (the small, bright yellow dot at the center of the photo) that have been trapped by a combination of laser beams and magnetic fields. The atoms, levitated in a vacuum by this magneto-optical trap, have a temperature less than a thousandth of a degree above absolute zero, yet they remain in the gas phase.

Copies of this report are available from:

Board on Physics and Astronomy

National Research Council

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Washington, DC 20001

www.nationalacademies.org/bpa