The Force of Nothing: Attraction, Repulsion, and Motion in the Quantum Void | Mehran Kardar (MIT)

The quantum vacuum is filled with fluctuations of the electromagnetic field. When material boundaries constrain these fluctuations, they exert measurable forces: the Casimir effect describes an attraction between uncharged conductors arising solely from the confinement of the quantum void. Discussions during two KITP programs were especially influential in connecting this remarkable quantum phenomenon to broader ideas of attraction, repulsion, and mechanical work. After introducing the origin and measurement of the Casimir force, Prof. Kardar will discuss whether it can be made repulsive, and why true levitation remains elusive in equilibrium. Extending these ideas beyond equilibrium reveals new possibilities: radiation pressure from heat, nonreciprocal materials that generate motion and work without contact, and rotating bodies that spontaneously emit light. Together, these examples show how the restless quantum vacuum continues to surprise us. ABOUT THE SPEAKER: Mehran Kardar is a leading Iranian-American theoretical physicist whose work has profoundly shaped modern statistical physics. He is particularly well known for the Kardar–Parisi–Zhang (KPZ) equation, which captures universal features of interface growth. His research spans a wide range of problems in statistical mechanics, including non-equilibrium collective behavior such as in active matter and deposition processes; disordered systems like spin and flux glasses; and soft-matter physics involvingpolymers, membranes, and gels. Kardar has also contributed to the understanding of fluctuation-induced phenomena (e.g., Casimir forces) and to biological physics. Mehran Kardar holds the Francis Friedman Professorship for physics at the Massachusetts Institute of Technology (MIT), and he is also affiliated with the New England Complex Systems Institute. Kardar earned a B.A. and an M.A. in Natural Sciences at Cambridge University, England. He completed his Ph.D. in physics at MIT in 1983 under Professor A.N. Berker. After serving as a Junior Fellow of the Harvard Society of Fellows (1983–1986) he joined the MIT faculty, where he has remained since. Throughout his distinguished career, Kardar has received numerous honors for both research and teaching. Early recognitions include the IBM Predoctoral Fellowship, Sloan Fellowship, and the Presidential Young Investigator Award. At MIT, he has earned multiple teaching prizes, such as the Edgerton Award and the John David Jackson Excellence in Graduate Physics Education Award. His scientific contributions have been acknowledged through the Guggenheim Fellowship (2001), the Simons Fellowship (2020), the Alexander von Humboldt Foundation Research Award (with which he visited the Max Planck Institute for Dynamics and Self-Organization and the University of Göttingen) and the prestigious 2025 IUPAP Boltzmann Medal. Kardar is a Fellow of the American Physical Society and the American Academy of Arts and Sciences, a member of the National Academy of Sciences, and recipient of the APS 2026 Lars Onsager Prize. He is also the author of two influential textbooks—Statistical Physics of Fields and Statistical Physics of Particles. __________________________________ KITP Public Lectures connect you with people and research that is transforming our understanding of the universe. This popular series takes advantage of the presence of the many distinguished scientists who visit KITP to collaborate on the most fascinating and challenging questions in their fields. Speakers have included, among others, Conny Aerts, Peter Galison, Asimina Arvanitaki, Murray Gell-Mann, John Grunsfeld, Stephen Hawking, Robert Kirshner, Nathan Lewis, and M. Cristina Marchetti. Talks have ranged from how stars ring, projects at the large hadron collider (LHC), how the brain works, challenges for global energy, the potential in the human genome, and black holes. Join the KITP Public Lecture Mailing List: https://www.kitp.ucsb.edu/outreach/pu... __________________________________ Learn more at: https://www.kitp.ucsb.edu Connect with KITP everywhere: 𝕏 https://x.com/@kitp_ucsb 🦋 https://kitp-ucsb.bsky.social ▶    / @kitp_ucsb   💻   / kavli-institute-for-theoretical-physics   __________________________________ The position of the KITP is that ownership and copyright of all online material -- slides, text, audio, video, and podcasts -- belongs to the author. KITP is providing dissemination for these materials but does not claim ownership. Any person citing these materials for scholarly purposes should provide an appropriate scholarly reference.