Gene activity determines the response of a living cell to environmental
signals and supports the stabilization of a well-determined cell state in the
face of intrinsic and environmental perturbations. How the molecular complexity
behind this gene activity self-organizes into stable cell states is one of the
most fascinating open questions in biophysics. From a physical perspective, the
living cell is a complex dynamical system with
numerous interacting molecular degrees of freedom; it is inherently and crucially a many-body phenomenon. After presenting the general problem of the emergence of stable cell states, I'll discuss our experimental approach allowing measurements of the long-term intracellular processes in dynamic cell populations, gaining insight into the genes' collective many-body dynamics. We show that two cell populations derived from a single steady-state mother population, fed by the same medium and exhibiting an invariant growth phenotype in response to an environmental challenge, displayed diverse gene expression patterns for genes essential for their metabolism. The gene expression patterns emerged from population-collective dynamics. This surprising result suggests that in a wide range of biological contexts, gene expression reflects a self-organization process coupled to collective population-environment dynamics.