The Physics of Active Matter
Assemblies of interacting self-driven entities form soft active materials with intriguing collective behavior and mechanical properties. Examples abound in nature on many scales, from the flocking of birds to cell migration in morphogenesis. They also include synthetic systems, from engineered microswimmers to self-catalytic colloids and autonomously propelled liquid crystals. What unifies these systems is that they are driven out of equilibrium by dissipative processes that act on each individual particle, hence break the time reversal symmetry of the dynamics at the microscale. This results in surprising behavior. For instance, active fluids flow with no externally applied driving forces, active gases do not fill their container, and active particles spontaneously organize when passive ones would not. Since time reversal symmetry of the microdynamics and the associated detailed balance of forward and reverse processes are built into the foundation of equilibrium statistical physics, the description of active systems poses a new theoretical challenge. In this talk I will discuss the physics of active matter with examples from both the living and non-living worlds. I will show that by combining minimal physical models with continuum theory and simulations we are making advances towards capturing quantitatively the laws of spontaneous organization of active systems. This theoretical progress has implication for both formulating design principles for new smart materials and understanding cellular and multicellular organization.
Cristina Marchetti is the William R. Kenan Distinguished Professor of Physics at Syracuse University, where she heads the Soft and Living Matter Program, and currently a Simons Distinguished Visiting Scientist at the Kavli Institute for Theoretical Physics (KITP) at the University of California Santa Barbara. She received her Laurea in physics from the University of Pavia, Italy, and her Ph.D. in physics from the University of Florida. She has held postdoctoral positions at the University of Maryland, Rockefeller University, and City College of CUNY. Marchetti is a versatile theoretical physicist who has worked on a broad range of problems including supercooled fluids, glasses and superconductors. Currently, she is interested in understanding the emergent behavior of soft and biological materials, from flocks of engineered microswimmers to cells in living tissues. Marchetti is currently co-editor of Annual Reviews of Condensed Matter Physics and co-Lead Editor of Physical Review X. She is a Fellow of the American Physical Society and of the American Association for the Advancement of Science, and a member of the American Academy of Arts and Sciences. She has held elected positions in the American Physical Society, and continues to play a leadership role in the scientific community.