# Loeb Lectures in Physics: M. Cristina Marchetti, "The Physics of Active Matter." November 14-16, 2022
**M. CRISTINA MARCHETTI**
Distinguished Professor of Physics
University of California Santa Barbara
**November 14-16, 2022**
***All lectures will be held in Jefferson 250 (17 Oxford Street) and streamed live via zoom (please see the [link below](#zoom))***
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Monday, November 14, 2022, @4:30pm:
"The Physics of Active Matter"
Birds flock, bees swarm and fish school. These are just some of the remarkable examples of collective behavior found in nature. Physicists have been able to capture some of this behavior by modeling organisms as "flying spins’’ that align with their neighbors according to simple but noisy rules. Successes like these have spawned a field devoted to the physics of active matter – matter made not of atom and molecules but of entities that consume energy to generate their own motion and forces. Through interactions, collectives of such active particles organize in emergent structures on scales much larger than that of the individuals. There are many examples of this spontaneous organization in both the living and non-living worlds: motor proteins orchestrate the organization of genetic material inside cells, swarming bacteria self-organize into biofilms, epithelial cells migrate collectively to fill in wounds, engineered microswimmers self-assemble to form smart materials. In this lecture I will introduce the field of active matter and highlight ongoing efforts by physicists, biologists, engineers, and mathematicians to model the complex behavior of these systems, with the goal of identifying universal principles.
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Tuesday, November 15, 2022, @4:30pm:
"Dynamics of active fluid interfaces"
There are many situations where active fluids coexist with passive ones. In bacterial swarms internal boundaries form separating cells of different type or separating live and dead cells. In cell biology the evidence for the formation of membraneless organelles has fueled interest in the role of active processes in liquid-liquid phase separation. Inspired by recent experiments that combine a microtubule-based active fluid with an immiscible binary polymer mixture, we have used numerical and analytical methods to explore how active stresses and associated flows modify the properties of the soft interfaces in a phase separating mixture. Experiments and theory have revealed a wealth of intriguing phenomena, including giant interfacial fluctuation, traveling interfacial waves, activity suppressed phase separation, and activity controlled wetting transitions.
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Wednesday, November 16, 2022, @4:30pm:
"Rheology of dense biological tissue"
Over the last decade there has been growing evidence demonstrating that dense biological tissue can spontaneously undergo transitions between a solid-like (jammed) state and a fluid-like (unjammed) state. The rheological state of the tissue in turn influences the transmission of mechanical deformations, which plays a central role in driving developmental processes, such as wound healing and morphogenesis, and tumor progression. Using computational models and analytical approaches, we have investigated the linear and nonlinear constitutive equations of confluent tissue, with no gaps between cells, under shear deformations. We find that an initially undeformed fluid-like tissue acquires finite rigidity above a critical applied strain and that solid-like tissue quickly exhibit nonlinear stress-strain response. We formulate a continuum model that couples cell shape to flow and captures both the tissue solid-liquid transition and its rich linear and nonlinear rheology.
***The lectures are sponsored by the Morris Loeb Lectureship Fund.***
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**M. Cristina Marchetti** is a Distinguished Professor of Physics at the University of California Santa Barbara. She was educated in Italy at the University of Pavia, earned her Ph.D. in the U.S. at the University of Florida, and joined the faculty at UC Santa Barbara in 2018, after thirty years on the faculty at Syracuse University. Marchetti is a theoretical physicist who has worked on a broad range of problems in condensed matter physics, including supercooled fluids, superconductors and driven disordered systems. Currently, she is interested in understanding the emergent behavior of active matter. The name refers to large collections of self-driven agents that exhibit organized behaviors on scales much larger than that of the individuals. Examples range from the flocking of birds to the sorting and organization of cells in morphogenesis, and include synthetic analogues, such as active colloids and engineered microswimmers. Marchetti is currently co-lead editor of the Annual Reviews of Condensed Matter Physics. 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 and of the US National Academy of Sciences. In 2019 she was awarded the inaugural Leo P. Kadanoff prize by the American Physical Society.
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