A closed classical system will tend to thermalize and maximize its entropy over time. The eigenstate thermalization hypothesis seeks to explain how this behaviour emerges from quantum systems in the classical limit. However, some quantum systems seem to resist thermalization because of phenomenons like ergodicity breaking, hilbert space fragmentation or quantum scarring.
To provide an intuitive understanding of those concepts, I provide examples of quantum cellular automata with different thermalizing properties and examine them according to known methods.