Perspective of Meta-Hierarchy Dynamics

The understanding of nature has been developed by separating and connecting elements in a reductive manner. For example, a spatio-temporal scale can provide us a clear picture of elemental separations. In biology, a function also gives us a useful picture to understand biological nature. Furthermore, a physical model also improves the outlook for understanding physical nature. These divided or connected elements, namely, scales, functions, and models form hierarchical structures in nature. On the other hand, fusion science explores various multi-scale and multi-physics phenomena, spreading over spatio-temporal scales from the microscopic to the macroscopic. In particular, collective motion causes structural formations not only in core plasmas but also material-facing ones. Therefore, fusion science has been an excellent subject for the application of the hierarchical approach. However, some problems have emerged with the progress of experimental and numerical research in fusion science. We often encounter phenomena that cannot be well understood by hierarchical separation. For these phenomena, beyond the conventional approaches for hierarchical systems, it is necessary to reconsider them with meta-perspectives, i.e., meta-hierarchy dynamics.