2015/05/31 by Alpha A. Lee, Dominic Vella, J. S. Wettlaufer +1
Physics and Astronomy · #Advanced Thermodynamics and Statistical Mechanics #Brownian motion #Casimir effect #Classical mechanics #Function (biology) #Micro and Nano Robotics #Non-equilibrium thermodynamics #Phenomenology (philosophy) #Physics #Quantum Electrodynamics and Casimir Effect #Quantum mechanics #Statistical physics #cond-mat.soft #cond-mat.stat-mech #physics.bio-ph
paper · pdf · doi:10.1073/pnas.1701739114
published as Proc. Nat. Acad. Sci. USA, vol. 114 (35), 9255-60 (2017)
arxiv created 2017/06/24 · openalex publication_date 2017/08/15 · arxiv updated 2020/07/06 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/06
Many biological systems are appropriately viewed as passive inclusions immersed in an active bath: from proteins on active membranes to microscopic swimmers confined by boundaries. The nonequilibrium forces exerted by the active bath on the inclusions or boundaries often regulate function, and such forces may also be exploited in artificial active materials. Nonetheless, the general phenomenology of these active forces remains elusive. We show that the fluctuation spectrum of the active medium, the partitioning of energy as a function of wavenumber, controls the phenomenology of force generation. We find that, for a narrow, unimodal spectrum, the force exerted by a nonequilibrium system on two embedded walls depends on the width and the position of the peak in the fluctuation spectrum, and oscillates between repulsion and attraction as a function of wall separation. We examine two apparently disparate examples: the Maritime Casimir effect and recent simulations of active Brownian particles. A key implication of our work is that important nonequilibrium interactions are encoded within the fluctuation spectrum. In this sense, the noise becomes the signal.