Phillips discusses ‘coldest stuff in universe’

In his lecture “Time, Einstein, and the Coldest Stuff in the Universe,” Dr. William D. Phillips entertained a packed room at Brooks-Rogers Recital Hall Thursday evening.

Phillips, 1997 Nobel Laureate in Physics, received the award along with Steven Chu of Stanford University, and French physicist Claude Cohen-Tannoudji last October, for their work advancing the techniques of laser cooling. A Fellow of the National Institute for Standards and Technology in Gaithersburg, Maryland, Phillips offered to come to Williams as part of a program of the American Physical Society.

Thursday evening’s lecture kept the audience laughing as Phillips peppered his talk with jokes and the use of appropriate cartoons from sources such as “The Far Side.” He also used a gyroscope and a spinning magnet to help explain how he and others have succeeded in cooling atoms down to temperatures in the range of one millionth of a degree above absolute zero. But before he began, the audience was given a taste of the formal awards ceremony of the Royal Swedish Academy of Sciences through a short video which Phillips brought with him.

The lecture was intended for a general audience, and Phillips proved himself adept at explaining the rather complex concepts and techniques in an interesting and easily understandable way. Before explaining how to cool atoms to extremely low temperatures, he discussed one of the important practical uses for this technique, which is the ability to make much more accurate atomic clocks. One use for extremely accurate atomic clocks is the Global Positioning System, which consists of an array of satellites each containing an atomic clock which is constantly broadcasting the time to receivers on earth. Because each signal takes a certain, brief amount of time to travel, the distance to each satellite can be determined, and the combination of three such pieces of information is enough to determine position in three dimensions.

Phillips then proceeded to explain the Doppler effect, the experience when a car passes and the pitch of the noise it makes seems higher if it is coming toward us, and lower when going away from us. This effect also puts a limit on the accuracy of atomic clocks. The only way to reduce this limit is to slow down the atoms. The problem normally encountered with slowing down (cooling) atoms is that the gas condenses into a liquid and finally freezes into a solid. This is where the technique of laser cooling enters the story.

Laser cooling makes use of the ability of light to impart a “push” on something. However, atoms will only absorb light and feel a push if it is a certain color, or frequency. By using six lasers which are tuned slightly below this resonant frequency in order to take advantage of the Doppler effect, the atoms will be pushed by each laser which it moves toward, and will be contained in what Phillips referred to as an “optical molasses” (a term he attributed to Steven Chu). The slowed atoms are at temperatures much lower than can be achieved with any sort of refrigerant.

Phillips explained that the temperatures achieved in various experiments were much lower than the temperatures predicted by current theory at the time. This was the experimental evidence which led to the need for a new theory, which he decided to reserve for the subject of the more technical talk he delivered at the physics colloquium on Friday, entitled “Optical Lattices: Atomic Physics Meets Steady State”.

Phillips, who received his bachelor’s degree from Juniata College, a liberal arts college in Pennsylvania, before studying at the Massachusetts Institute of Technology, where he received his Ph.D, also discussed one of the most talked about developments following improved methods of laser cooling: the observation of Bose-Einstein condensation, predicted by Einstein in the 1920s and not accomplished until 1995.

One of the main objectives of Phillips’s visit to Williams was to meet and talk with students. A reception in the Faculty House follwed Thursday’s lecture. Phillips ate dinner with faculty and stu dents on Thursday, spoke at three classes during his stay, ate lunch with students and faculty on Friday, and delivered the colloquium talk Friday afternoon.

Information concerning the 1997 Nobel Prize in Physics can be found on the World Wide Web at the following addresses: and