US physicist who with French physicist Claude Cohen-Tannoudji and US physicist Steven Chu was awarded the Nobel Prize for Physics in 1997 for the development of techniques using laser light to cool and trap atoms to extremely low temperatures.
Atoms and molecules of air move at very high speeds, in the order of 4,000 km/2,490 m per hour at room temperature, and this makes it difficult to study them and find out about their structures. Cooling a gas will reduce the speed of the atoms, but eventually this leads to condensation and then freezing to a solid form. In these states the atoms are too close together to determine individual properties. Chu developed a technique using laser light to cool gas molecules in a vacuum that allowed the examination of individual species. In 1988, Phillips expanded on the techniques developed by Chu and achieved cooling down to 0.00004 kelvin. Absolute zero is zero degrees kelvin, or −273.15°C/−459.67°F. However, this temperature was six times lower that was predicted by the theory governing laser cooling. Cohen-Tannoudji showed that the existing theory, which was based on a simplified model of the atom, did not adequately describe the complex system that existed at extremely low temperatures. His refined theories proved that Phillips's observation was correct and it was the theory that was at fault. These laser cooling techniques have allowed scientists to investigate states of matter known only in theory. Notably, the discovery of Bose-Einstein condensation in atomic gases, predicted by physicist Albert Einstein and Satyendra Bose in the 1920s.
Phillips was born in Wilkes-Barre, Pennsylvania, USA. He received his PhD in physics from the Massachusetts Institute of Technology in 1976 and became a staff member of the National Bureau of Standards, now known as the National Institute of Standards and Technology, Gaithersburg, Maryland, in 1978.