Quirky physics brown bag series prizes unusual questions

The subscribers to Thomas Witten’s brown bag e-mail list receive a terse message from him almost every week.

These invitations to the Materials Research Science and Engineering Center’s Friday brown bag luncheons name the topic of the week and little else. The titles are almost always quirky. Recent examples have included “In Search of Sandy Fingering Instability,” “Sights and Sounds of Nanoparticle Drums,” and “Steppin’ vs. STOMPIN on Cornstarch.”

The luncheons have acquired their own mystique under the stewardship of Witten, the Homer J. Livingston Professor in Physics, having become a mainstay of intellectual life in the Materials Research Center and the James Franck Institute.

“This one’s for questions. There are other seminars for answers,” noted Leo Kadanoff, the John D. and Catherine T. MacArthur Distinguished Service Professor Emeritus in Physics.

The speakers remain putatively unknown until the bag lunch attendees show up in the ground-floor conference/lunch room in the east wing of the Gordon Center for Integrative Science. Witten approaches speakers on short notice to give relatively brief, informal presentations that will provoke a fusillade of questions, discussions and suggestions.

“It is not a polished talk that Tom is looking for. He’s looking for some unsolved mystery or question,” said Ka Yee Lee, professor in chemistry and MRSEC director. “Our job really is to listen and to help out in the detective work.”

The UChicago bag lunch series stems from a similar luncheon program started by Phil Pincus at the University of California, Santa Barbara’s Institute for Theoretical Physics. Witten paid an extended visit to the institute in the 1980s, when he was a faculty member at the University of Michigan.

He had been driving across country thinking about a problem that had puzzled him. After making some progress, he got stuck. When Witten related this to Pincus after arriving in Santa Barbara at 10 a.m., the latter said, “Perfect. You’re talking at 12 o’clock, when lunchtime comes.”

Witten found a receptive and helpful audience. “They saw some things I couldn’t see and so I said, ‘Hey, this really works.’”

Pincus and Witten later worked together at Exxon Corp., where they instituted a similar bag-lunch series. “We said, ‘This is important for the life of the lab,’” Witten said. “And then I got a job here and the same thing was true.”

The coffee-stain problem

Sidney Nagel, the Stein-Freiler Distinguished Service Professor in Physics, first raised the coffee-stain problem at a Friday bag lunch in the mid-1990s. Why, he asked, does a dried coffee stain always leave a dark ring at its outer edge?

“Everybody got interested in the coffee-stain problem and word got around, and so the next time of course there were 30 people in the room,” Nagel said. Witten recalled that people would run out of the room to prepare a coffee stain, then come back and say, “See, it’s like I told you.”

The discussions culminated in the publication of an article by Nagel, Witten and others in the Oct. 23, 1997 issue of Nature showing that the coffee stain is an example of an important and general phenomenon.

Another memorable seminar occurred approximately 10 years ago when Lee, the chemistry professor, presented some data at a MRSEC luncheon about how the monolayer materials that she works with respond to lateral stress. The monolayers, which measure only one molecule in thickness, simulate the dynamics of lung surfactant, a microscopically thin membrane that facilitates breathing.

Nagel, who was in the audience, asked if the phenomenon occurring in her lab had anything to do with earthquakes. He suggested that Lee’s group produce the equivalent of a seismogram to better understand monolayer dynamics.

The folds that Lee and her team were seeing measured only a fraction of an inch long at most, while crustal movements in earthquakes take place over a span of miles. How, she wondered, could the two phenomena possibly relate?

“But that planted a seed in our heads,” Lee said, and when her group later decided to conduct an image analysis of the crumpling and folding, they remembered Nagel’s suggestion.

One of Lee’s graduate students at first tried to assess video of the folding frame-by-frame with the naked eye, but this method yielded a rather small statistical sample.

Lee’s group then began working with Witten and one of his graduate students to modify one of the computer programs they had written for motion analysis. That gave rise to a “seismogram” that pinpointed 500 spots in a particular frame for statistical analysis. The team published the “seismogram” in a 2006 paper in the Journal of Physical Chemistry B Letters.

“It really was triggered by this completely out-of-the blue comment from our perspective, because we’re looking at something really small,” Lee said. Nagel had found a way to connect the nanoscopic scale of the material that Lee’s group was working on to the larger-scale materials that he focused on.

Such unexpected developments have helped to unite UChicago material scientists no matter what their specialty. Said Nagel, “It helps bring us all together so that we really have much closer collaboration between people.”