October 19, 2005
American Center for Physics
College Park, MD
What is time? Even Einstein had a hard time answering this question, but his 1905 paper on Relativity changed our understanding of time in fundamental and non-intuitive ways. In spite of all this, we can measure time more accurately than any other quantity. Atomic clocks are the most accurate timepieces ever made, and are essential for such features of modern life as synchronization of high speed communication and the operation of the Global Positioning System (GPS) that guides aircraft, cars, boats and backcountry hikers to their destinations. The limitations of atomic clocks come from the thermal motion of the atoms: hot atoms move rapidly and experience the time shifts that Einstein predicted.
Contrary to intuition, we can cool the thermal motion of atoms by shining laser light on them. With laser cooling, we chill gases to less than one millionth of a degree above Absolute Zero. The slowly moving atoms in such a gas allow us to make even more accurate clocks, already so good that they would gain or lose only a second in 40 million years. Among the possible applications of such incredible accuracy are new tests of Einstein's theory of gravity.
Laser cooling has also made possible the observation of a long-standing prediction of Einstein: Bose-Einstein condensation. The resulting"new state of matter," hailed as one of the most important recent scientific developments, has reached temperatures less than one billionth of a degree above absolute zero
William D. Phillips received a B.S. in Physics from Juniata College in 1970 and a Ph.D. from MIT in 1976. After two years as a Chaim Weizmann postdoctoral fellow at MIT, he joined the staff of the National Institute of Standards and Technology (then the National Bureau of Standards) in 1978. He is a NIST Fellow, leader of the Laser Cooling and Trapping Group in the Atomic Physics Division of NIST's Physics Laboratory, and is a Distinguished University Professor at the University of Maryland, College Park. In 1997, Dr. Phillips shared the Nobel Prize in Physics "for development of methods to cool and trap atoms with laser light."