Advanced core-to-core network for the physics of self-organizing active matter

JSPS Core to Core Programme: A. Advanced Centre Formation Type

Active particle systems, also known as self-driven or active matter, refer to matter and objects that sustain spontaneous motion while consuming energy, along with their aggregates. Unlike ordinary, inactive matter, active matter is in a strong non-equilibrium state due to the continuous injection and dissipation of energy. Consequently, traditional statistical thermodynamics methods based on free energy, valid for ordinary matter, are not applicable for predicting and analyzing the behavior of particle populations. Examples of active matter systems include those of biological origin, such as populations of fish and micro-organisms (e.g., bacteria) swimming in water (Fig. 1: left), flocks of birds and insects in flight (Fig. 1: middle), and aggregates of cells migrating and multiplying on a substrate or inside a living organism (Fig. 1: right). Other systems include soft-matter systems driven by external forces (e.g., Quincke rollers), biosimulated systems that consume chemical energy to generate driving forces in their constituents (e.g., oil droplets on the water surface and camphor boats), active Brownian particle systems with directed self-propulsion in addition to random thermal motion, and micro-swimming microorganisms simulated as microscopic machines. In recent years, various artificial active matter systems, such as microswimmer systems that simulate swimming micro-organisms as micro-machines, have also been intensively studied from a physics perspective. These active matter systems exhibit non-trivial and peculiar collective motions, not found in ordinary materials, due to self-organization, yet the physical mechanisms and emergence principles behind these phenomena remain a mystery. Thus, answering the important unsolved question in physics, "How can active matter systems, which interact only locally, have emergent global collective motions?" is the focus of this research network. Additionally, the core nodes mutually organize International Research Meetings and send young researchers abroad to enhance their research skills and internationalization.